Traction, Active Handling, reduced Engine Power
12-11-2007, 09:55 AM
#1
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Traction, Active Handling, reduced Engine Power
I bought a 99 coupe about 6 months ago. I had problems within a month with the warning lights popping up with the following messages, "service active handling", "service traction system", and then those were followed by "reduced engine power". The reduced engine power message was followed by a serious reduction in the engine's output. I took it to the local Chevrolet dealer who tested it, time and again but could not get it to duplicate the problem long enough to get a good code for repair. Finally after about 3 trips to the shop, they were able to determine the problem was in the ABS module, which they replaced.
This was in early September. The problem was eliminated until mid December, when it did the same thing again. I parked the car at work and drove home a couple of hours later at which time the warnings and reduced engine power did not occur but the check engine light remained on. The next day, none of the problems existed. I know however, from my experiences during the summer months that it can go away and come back.
Any ideas on what the cause could be?
This was in early September. The problem was eliminated until mid December, when it did the same thing again. I parked the car at work and drove home a couple of hours later at which time the warnings and reduced engine power did not occur but the check engine light remained on. The next day, none of the problems existed. I know however, from my experiences during the summer months that it can go away and come back.
Any ideas on what the cause could be?
12-11-2007, 05:56 PM
#2
Burning Brakes
Member Since: Jan 2006
Location: Magnolia Greens NC
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Read This...
Jwally...when you say "they replaced the ABS module"..was it the BPMV?...or the EBCM?...any way, here's what you need to know...AND, I'll need your email address if you want me to send all the PHOTOS that go with this tutorial....
The Basics
Let's cover some basic information on AH, TC, and ABS. In simple terms, these three systems combine data from wheel speed sensors, yaw rate sensors, steering wheel position sensors, along with brake and throttle inputs to determine what the driver wants to do and detects any lose of traction and take corrective action by pulling back on the throttle, activating brakes on individual wheels, or releasing brake pressure as needed to maintain traction.
What goes wrong
When there is a problem anywhere in the system, the computer does not know what's going on with the car or cannot respond correctly. Rather than risking the wrong response which could potentially wreck you car, the whole system is simply disabled for the remainder of the ignition cycle. At this time you will see the ABS and Traction Control warning indicators illuminated on the instrument cluster along with the following messages on the Driver Information Center (DIC):
- Service ABS
- Service Traction System
- Service Active Handling
At this point, you can safely continue to drive your car, just remember that your electronic driving aids are no longer functioning so you should adjust your driving habits accordingly.
Troubleshooting
As I said before, when there is a problem the system is deactivated for the remainder of the ignition cycle, so sometimes everything will go back to normal if you just turn off the car and restart it. If that corrects the problem, it was either a glitch in the system, a lose connection that's going to come back soon or an early sign of a future failure that is coming. Even though the system is now functional it is still beneficial to continue to trouble shoot. The history code should give you a good idea of what to check
The next step is to see where the fault is. If you have several different codes write them down, clear them, and see which ones come back the next time you start the car. At this point, I'm betting that the codes point to either the EBCM or the wheel speed sensors. We'll get to the wheel speed sensors later, for now, let's get to the EBCM.
Electronic Brake Control Module
The most common code for the EBCM is C1214 - Sol Valve relay Contact or coil CKT Open. This code is set when the system voltage is less than 8 volts for 0.23 seconds. Since our goal is to fix this for the lowest price possible, we'll start checking things we can fix for free
The EBCM sits between the engine and radiator. You can see it in the picture on the left below. The EBCM is on the left with the large wire harness coming into it and the sticker on top. The Brake Pressure Modulator Valve (BPMV) in on the right with the brake lines coming out. The EBCM is a dry module, meaning that you can change it out without having to worry about bleeding the ABS system. All of the brake fluid is contained within the BPMV. The coils (seen in the picture on the right below) fit over small spools that have valves inside them. The valves are operated by an electromagnetic field supplied by the coils.
Start by doing a quick visual inspection of the wires. If there are any obvious signs of damage, you've likely found the problem. One member had a problem with the wires rubbing the serpentine belt
Also check to make sure the wire harness has a good connection. If the connection appears solid disconnect it (see step 3 in the replacement instructions below) check the pins to ensure that they have not been bent or damaged in any way. If there is any sign of corrosion, clean it off. Once everything looks good, reseat the harness.
Next, let's move on to the grounds. The EBCM is grounded to the chassis on the left frame rail, just forward of the engine. It's the Black box right in the middle of the picture. As you can see, it's real easy for dirt and moisture to get in that area which isn't exactly good for electronic components. Even if you never drive your car in the rain, it'll still get wet when you wash it, and that could be enough
Start by unbolting the chassis ground, then take the chassis ground connector apart.
These pictures show the corrosion that can build up in the ground connector. If you chassis grounds look like this one, you've probably found the problem. Even if they don't, go ahead and clean it up with a wire brush before putting it back together. Also clean off the chassis and bolt to make sure you've got a good clean ground.
*If you are having any other electrical issues, it's a good idea to check the grounds. These pictures show where the other grounds are.
It's unlikely, but before you break out you credit card and forking over your hard earned money, it's a good idea to check the fuses. One fuse box is located under the hood beside the battery, the second one is under the passenger side of the dash. Remove the floor mat and you will see the access panel. Just pull the fuses out and do a quick visual check.
On the left, you see a good fuse, on the right is a bad fuse
At this point, we know all of the wires are good, but for some reason enough voltage is not getting to the system. It is possible that your battery is not functioning properly. If your battery is a couple of years old, has been drained and recharged a couple of times it might be a good idea to go ahead and replace your battery. This is a long shot for EBCM issues, but I think it's worth a shot before spending several hundred dollars for a new EBCM and you're going to have to replace it eventually anyways. Old batteries can cause a variety of minor electrical issues and you likely have a bunch of history codes for minor issues if the battery is causing the problem.
Now on the EBCM itself. If the electrical contacts inside the relay are dirty or burnt, the vibration from striking the module may change the symptoms or may clear them up for a while. This is by no means a fix or a cure all, in fact it could make it worse or it may not do anything, it's just something to try. Use a small plastic hammer or something similar, lightly tap the front of the EBCM on the lower right corner of the module. The area will be on the right hand side of the lower electrical connection seen in the picture below.
At this point, You've got to additional possibilities. Replace the EBCM or replace both the EBCM and the BPMV. The service manual calls for you to measure the resistance between each pump motor control circuit and the housing of the BPMV, if that checks our okay, you replace the EBCM if not you replace them both. Since most people do not have the equipment to do this the best we can do is to replace the EBCM. If that doesn't work, you'll have to go back and replace the BPMV.
The procedure for replacing the EBCM is very simple. The only special tool you need is a T-20 torx screw driver. I have a Craftsman tool set that has a 1/4" drive screwdriver with and adapter for many different size bit. Unfortunately, the adapter was to long to fit between the EBCM and water pump, so I purchased a set of Craftsman 5 pc. torx screwdriver set that worked fine. A flathead screwdriver may also be needed to pry apart the EBCM from the BPMV
1 - make sure the car is off.
2 - you will probably need to remove the airbridge to get to the EBCM.
3 - remove the wire harness by first removing the white plastic clip that locks it in place (I cut it off and replaced it with a zip-tie) (picture 1), then lift gray handle and pull back on the wire harness (picture 3). At this point, you will be able to see the second wire connection that is removed by pulling down (picture 3).
4 - The service manual call for you the remove the 2 insulator nuts that hold the BPMV to the brackets and lift the EBCM/BPMV out of the bracket. I do not think this step is necessary because there is plenty of room while it is still in the bracket and you do not gain much additional clearance since the brake lines restrict the movement.
5 - Remove the 6 T-20 torx screws connecting the EBCM and BPMV - 1 on each corner and 2 on the sides (picture 2).
6 - "Separate the EBCM from the BPMV by gently pulling apart until separated" - I should start laughing here, but it's not that funny. It's been my experience that anytime the instructions call for you to do something gently, nothing gentle is going to work. In this case, I had to use a flathead screw driver to brake the seal. Once it moved a little, the rest was easy. In addition to the rubber seal, each of the 12 holes you see in picture 3 have a peg in them from the BPMV. Don't go crazy, but be prepared to force them apart.
7 - At this point, all you've got to do is put it all back together. push the new EBCM onto the BPMV.
8 - Replace the 6 T-20 torx screws
9 - reconnect the wire harness
10 - put the intake back on
picture 1 picture 2 picture 3
At this point, the AH/TC/ABS should work normally. If not, you've also got a problem with the BPMV. Although you could replace the BPMV yourself, you have to bleed the ABS system which requires Tech II. For those of you like me that don't have access to Tech II, you've got 2 options. Replace the BPMV yourself and tow the car to a shop with Tech II to have it bled, or just take it in to have the BPMV replaced. The advantage is that you've already done all of the trouble shooting so you want have to pay the mechanic to diagnose the problem for you.
Wheel Speed Sensors
Back to the wheel speed sensors. Code C1221 - 1228 indicate that one of the wheel speed sensors is either sending a bad signal or no signal. Start by checking the connections. The wheel speed sensors are integrated into the wheel bearing/hub assembly pictured below. The wire coming out of the back is the connection for the wheel speed sensors. Verify that the connector are not broken, damaged, or corroded in any way. Pay particular attention to the female end.
The wire coming out of the wheel speed sensor connects to and 18" jumper harness, then to the main harness. It is very common for people to have a weak female pin in one of those connections. If all of that checks out good, Swap the jumper harness from side to side. For example if the left front is bad, swap it over to the right front. and install the good one from the right front to the left side. Then clear the trouble code. If the trouble code is now on the right side, you know the wire harness is the problem. If the code is still on the left side after swapping the jumper harnesses, you know the problem is inside the wheel speed sensors.
If all the wires check out good, it's time to take a trip to Auto Zone for a new set of bearings. You can buy replacement AC Delco bearing from your dealer if you want to, or get the exact same bearing in a different box for half the price (~$150) from Auto Zone, you decide. The bearings should be replaced in axel sets, so if your left front is bad, you have to replace the right front too. While your at it, this is a good time to upgrade the lug studs and add spindle ducts.
Replacement part sources
New EBCMs. Below is a list of part #s and estimated prices from Fred Beans to give you an idea of what you should pay.
Part Number: 9367071
All 1999-2000 w/o Control Active Brakes: $486.40
An alternative to buying a new one is to have your original rebuilt.
For EBCM repair/replace:
Call Brandon
877-648-7530 at ABS FIXER
$150. plus UPS....warranted as long as You own it
The Basics
Let's cover some basic information on AH, TC, and ABS. In simple terms, these three systems combine data from wheel speed sensors, yaw rate sensors, steering wheel position sensors, along with brake and throttle inputs to determine what the driver wants to do and detects any lose of traction and take corrective action by pulling back on the throttle, activating brakes on individual wheels, or releasing brake pressure as needed to maintain traction.
What goes wrong
When there is a problem anywhere in the system, the computer does not know what's going on with the car or cannot respond correctly. Rather than risking the wrong response which could potentially wreck you car, the whole system is simply disabled for the remainder of the ignition cycle. At this time you will see the ABS and Traction Control warning indicators illuminated on the instrument cluster along with the following messages on the Driver Information Center (DIC):
- Service ABS
- Service Traction System
- Service Active Handling
At this point, you can safely continue to drive your car, just remember that your electronic driving aids are no longer functioning so you should adjust your driving habits accordingly.
Troubleshooting
As I said before, when there is a problem the system is deactivated for the remainder of the ignition cycle, so sometimes everything will go back to normal if you just turn off the car and restart it. If that corrects the problem, it was either a glitch in the system, a lose connection that's going to come back soon or an early sign of a future failure that is coming. Even though the system is now functional it is still beneficial to continue to trouble shoot. The history code should give you a good idea of what to check
The next step is to see where the fault is. If you have several different codes write them down, clear them, and see which ones come back the next time you start the car. At this point, I'm betting that the codes point to either the EBCM or the wheel speed sensors. We'll get to the wheel speed sensors later, for now, let's get to the EBCM.
Electronic Brake Control Module
The most common code for the EBCM is C1214 - Sol Valve relay Contact or coil CKT Open. This code is set when the system voltage is less than 8 volts for 0.23 seconds. Since our goal is to fix this for the lowest price possible, we'll start checking things we can fix for free
The EBCM sits between the engine and radiator. You can see it in the picture on the left below. The EBCM is on the left with the large wire harness coming into it and the sticker on top. The Brake Pressure Modulator Valve (BPMV) in on the right with the brake lines coming out. The EBCM is a dry module, meaning that you can change it out without having to worry about bleeding the ABS system. All of the brake fluid is contained within the BPMV. The coils (seen in the picture on the right below) fit over small spools that have valves inside them. The valves are operated by an electromagnetic field supplied by the coils.
Start by doing a quick visual inspection of the wires. If there are any obvious signs of damage, you've likely found the problem. One member had a problem with the wires rubbing the serpentine belt
Also check to make sure the wire harness has a good connection. If the connection appears solid disconnect it (see step 3 in the replacement instructions below) check the pins to ensure that they have not been bent or damaged in any way. If there is any sign of corrosion, clean it off. Once everything looks good, reseat the harness.
Next, let's move on to the grounds. The EBCM is grounded to the chassis on the left frame rail, just forward of the engine. It's the Black box right in the middle of the picture. As you can see, it's real easy for dirt and moisture to get in that area which isn't exactly good for electronic components. Even if you never drive your car in the rain, it'll still get wet when you wash it, and that could be enough
Start by unbolting the chassis ground, then take the chassis ground connector apart.
These pictures show the corrosion that can build up in the ground connector. If you chassis grounds look like this one, you've probably found the problem. Even if they don't, go ahead and clean it up with a wire brush before putting it back together. Also clean off the chassis and bolt to make sure you've got a good clean ground.
*If you are having any other electrical issues, it's a good idea to check the grounds. These pictures show where the other grounds are.
It's unlikely, but before you break out you credit card and forking over your hard earned money, it's a good idea to check the fuses. One fuse box is located under the hood beside the battery, the second one is under the passenger side of the dash. Remove the floor mat and you will see the access panel. Just pull the fuses out and do a quick visual check.
On the left, you see a good fuse, on the right is a bad fuse
At this point, we know all of the wires are good, but for some reason enough voltage is not getting to the system. It is possible that your battery is not functioning properly. If your battery is a couple of years old, has been drained and recharged a couple of times it might be a good idea to go ahead and replace your battery. This is a long shot for EBCM issues, but I think it's worth a shot before spending several hundred dollars for a new EBCM and you're going to have to replace it eventually anyways. Old batteries can cause a variety of minor electrical issues and you likely have a bunch of history codes for minor issues if the battery is causing the problem.
Now on the EBCM itself. If the electrical contacts inside the relay are dirty or burnt, the vibration from striking the module may change the symptoms or may clear them up for a while. This is by no means a fix or a cure all, in fact it could make it worse or it may not do anything, it's just something to try. Use a small plastic hammer or something similar, lightly tap the front of the EBCM on the lower right corner of the module. The area will be on the right hand side of the lower electrical connection seen in the picture below.
At this point, You've got to additional possibilities. Replace the EBCM or replace both the EBCM and the BPMV. The service manual calls for you to measure the resistance between each pump motor control circuit and the housing of the BPMV, if that checks our okay, you replace the EBCM if not you replace them both. Since most people do not have the equipment to do this the best we can do is to replace the EBCM. If that doesn't work, you'll have to go back and replace the BPMV.
The procedure for replacing the EBCM is very simple. The only special tool you need is a T-20 torx screw driver. I have a Craftsman tool set that has a 1/4" drive screwdriver with and adapter for many different size bit. Unfortunately, the adapter was to long to fit between the EBCM and water pump, so I purchased a set of Craftsman 5 pc. torx screwdriver set that worked fine. A flathead screwdriver may also be needed to pry apart the EBCM from the BPMV
1 - make sure the car is off.
2 - you will probably need to remove the airbridge to get to the EBCM.
3 - remove the wire harness by first removing the white plastic clip that locks it in place (I cut it off and replaced it with a zip-tie) (picture 1), then lift gray handle and pull back on the wire harness (picture 3). At this point, you will be able to see the second wire connection that is removed by pulling down (picture 3).
4 - The service manual call for you the remove the 2 insulator nuts that hold the BPMV to the brackets and lift the EBCM/BPMV out of the bracket. I do not think this step is necessary because there is plenty of room while it is still in the bracket and you do not gain much additional clearance since the brake lines restrict the movement.
5 - Remove the 6 T-20 torx screws connecting the EBCM and BPMV - 1 on each corner and 2 on the sides (picture 2).
6 - "Separate the EBCM from the BPMV by gently pulling apart until separated" - I should start laughing here, but it's not that funny. It's been my experience that anytime the instructions call for you to do something gently, nothing gentle is going to work. In this case, I had to use a flathead screw driver to brake the seal. Once it moved a little, the rest was easy. In addition to the rubber seal, each of the 12 holes you see in picture 3 have a peg in them from the BPMV. Don't go crazy, but be prepared to force them apart.
7 - At this point, all you've got to do is put it all back together. push the new EBCM onto the BPMV.
8 - Replace the 6 T-20 torx screws
9 - reconnect the wire harness
10 - put the intake back on
picture 1 picture 2 picture 3
At this point, the AH/TC/ABS should work normally. If not, you've also got a problem with the BPMV. Although you could replace the BPMV yourself, you have to bleed the ABS system which requires Tech II. For those of you like me that don't have access to Tech II, you've got 2 options. Replace the BPMV yourself and tow the car to a shop with Tech II to have it bled, or just take it in to have the BPMV replaced. The advantage is that you've already done all of the trouble shooting so you want have to pay the mechanic to diagnose the problem for you.
Wheel Speed Sensors
Back to the wheel speed sensors. Code C1221 - 1228 indicate that one of the wheel speed sensors is either sending a bad signal or no signal. Start by checking the connections. The wheel speed sensors are integrated into the wheel bearing/hub assembly pictured below. The wire coming out of the back is the connection for the wheel speed sensors. Verify that the connector are not broken, damaged, or corroded in any way. Pay particular attention to the female end.
The wire coming out of the wheel speed sensor connects to and 18" jumper harness, then to the main harness. It is very common for people to have a weak female pin in one of those connections. If all of that checks out good, Swap the jumper harness from side to side. For example if the left front is bad, swap it over to the right front. and install the good one from the right front to the left side. Then clear the trouble code. If the trouble code is now on the right side, you know the wire harness is the problem. If the code is still on the left side after swapping the jumper harnesses, you know the problem is inside the wheel speed sensors.
If all the wires check out good, it's time to take a trip to Auto Zone for a new set of bearings. You can buy replacement AC Delco bearing from your dealer if you want to, or get the exact same bearing in a different box for half the price (~$150) from Auto Zone, you decide. The bearings should be replaced in axel sets, so if your left front is bad, you have to replace the right front too. While your at it, this is a good time to upgrade the lug studs and add spindle ducts.
Replacement part sources
New EBCMs. Below is a list of part #s and estimated prices from Fred Beans to give you an idea of what you should pay.
Part Number: 9367071
All 1999-2000 w/o Control Active Brakes: $486.40
An alternative to buying a new one is to have your original rebuilt.
For EBCM repair/replace:
Call Brandon
877-648-7530 at ABS FIXER
$150. plus UPS....warranted as long as You own it
Last edited by trussme; 12-11-2007 at 05:58 PM.
12-11-2007, 08:16 PM
#3
Tech Contributor
Member Since: Dec 1999
Location: Anthony TX
Posts: 32,736
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CI 6,7,8,9,11 Vet
St. Jude Donor '08
PLEASE read and post all your DTC's using the DIC in your C5. Heres how:
These are the absolute best C5 Diagnostic Trouble Code (DTC) web sites!!!
http://www.corvettedoctor.com/Code_Main.html
http://www.corvettedoctor.com/index.html
Go to “technical data base” and then to “Corvette ECM Computer Codes”. Then select your year car. Read the instructions and then scroll down to the "READ MORE" window to view the code definitions.\
Here is another very good site:
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
Make sure to include the H or C suffix!!
The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold OPTIONS
4) While holding OPTIONS, press FUEL four times within a 10-second period.
Initially, on-board diagnostics go into an Automatic Mode which shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each. ( i.e. PCM = 4 codes)
If none are present in a given module, you will see No More Codes on the display.
There are two kinds of diagnostic codes, Current and History designated with a letter suffix, C or ;H. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes.
More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present;
press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET
To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.
These are the absolute best C5 Diagnostic Trouble Code (DTC) web sites!!!
http://www.corvettedoctor.com/Code_Main.html
http://www.corvettedoctor.com/index.html
Go to “technical data base” and then to “Corvette ECM Computer Codes”. Then select your year car. Read the instructions and then scroll down to the "READ MORE" window to view the code definitions.\
Here is another very good site:
http://www.obd-codes.com/trouble_cod...d-ii-codes.php
Make sure to include the H or C suffix!!
The Diagnostic Display Mode is entered with the following procedure:
1) Turn on the ignition but don't start the engine.
2) Press the RESET button to turn off any warning messages. (i.e. door open, trunk open ect)
3) Press and hold OPTIONS
4) While holding OPTIONS, press FUEL four times within a 10-second period.
Initially, on-board diagnostics go into an Automatic Mode which shows diagnostic codes in a pre-set sequence: PCM - TCS - RTD - BCM - IPC - RADIO - HVAC - LDCM - RDCM - SCM - RFA. All codes will be displayed for each. ( i.e. PCM = 4 codes)
If none are present in a given module, you will see No More Codes on the display.
There are two kinds of diagnostic codes, Current and History designated with a letter suffix, C or ;H. A current code indicates a malfunction is present in the module displaying data. A history code indicates a problem existed sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it's potential evidence of a previous problem, now resolved, that was not removed by clearing the codes.
More likely it's an indication of an intermittent malfunction.
Intermittent codes are the most challenging of the diagnostics. An intermittent code may have happened once, may have happened more than once but is inconsistent or may be happening on a regular basis but not at the time the codes are displayed. History codes can also be caused by a current malfunction in a system that is not operating at the time codes are displayed. An example is the rear window defogger which doesn't operate until the Body Control Module detects engine rpm. For history codes set by a module that does not operate with the key on and engine off, a special diagnostic tool called a Scan Tester is necessary to properly diagnose the malfunction.
Once the system has displayed all modules, it goes into the manual mode which allows selection of each module using combinations of Driver Information Center buttons. Manual mode can also be entered during the automatic sequence by pressing any button except E/M. Once the display shows Manual Diagnostics, select a module by pressing the OPTIONS button to go forward or the TRIP button to go back. Once a module is selected, a code is displayed, and if more than one are present;
press GAGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase codes in a given module, press RESET
To reset the codes once in manual mode, press and hold RESET until it displays NO CODES Press OPTIONS to go to the next module. Repeat the steps until you have reset the codes in all the computer modules.
NOTE!! Only reset the codes IF you want to - it is NOT necessary to do this. Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory. If you clear the code/s, and extinguish the Check Engine Light, your emissions status ready will NOT allow you to pass an emissions test until you have completed the required driving cycles.
Once you have the codes, the next question is: What to do with the information?
First, consult the factory service manual. Any serious C5 Do-It-Yourself owner should invest in the Corvette Service Manual of the appropriate model year. The Service Manual is really a requirement if you want to understand and work on your C5.
