IMPORTANT ELECTRICAL INFORMATION (Long!)
Ordered a brand new one for like $55 (I think) - Vette tax for sure.
But my C5 is a DD so I need to keep the moisture out.
My 98 coupe would get the infamous "REDUCED ENGINE POWER", "TRACTION CONTROL FAILURE" and a host of random failure codes. After many, many hours of troubleshooting, replacing the BCM and TAC module, I solved most of the driveability issues. Still getting the random DTC failure codes, I thought that I may be having ground issues. Back in June I cleaned ALL of the chassis grounds and the car virtually stopped throwing the "RANDOM" DTC failure codes. Just moving the wires in the chassis ground connector was enough to change the indications and make the issues stop happening.
I had a chance to speak with some GM C5 Trouble Desk Engineers when I went to Bowling Green KY in April and they pointed out that MANY of the C5 electrical issues can be directly linked to chassis ground problems. The engineer even went as far as to recommending that I chop off the factory under hood chassis ground connectors and combine all of the wires into a single ground lug. Not wanting to just LOP off the factory connector, I took a chance and disassembled one of the ground plug connectors and to my surprise it was indeed full of corroded connections.
I strongly recommend that any C5 owner that has had or who are having electrical issues, examine and clean the chassis ground connectors. This may save you from needlessly replacing expensive electronics modules. Each ground connector can be disassembled and cleaned in about 20 min.
Just cleaning the metal ground connection between the chassis and the plug is only a band aid solution. Now that I look back, when I cleaned my chassis grounds and initially solved my issues, I believe that when the connector is being removed to clean the connection between chassis and the connector, just the wires being moved inside the plug is what changed the indications and made everything work better.
Disassembly of the chassis ground plug and cleaning the contacts inside the connector is the correct method of solving the issue!
I took some pictures of the under hood chassis ground connector and the corrosion that was in it. I cleaned the two connections on the frame rails and the left one was significantly corroded! Taking it apart and cleaning it is a very straight forward procedure and I believe that if you follow this recommendation, you will be on the way to solving the many of the electrical issues.
Here are some detailed pictures of the ground connector and the corrosion that was found inside it!
Picture of under hood Chassis Ground connector G-101

Corrosion inside connector! (You ain't seen nothing yet!)
[IMG]
[/IMG] Next three photos are of the corrosion found on the connector terminals!
[IMG]
[/IMG] [IMG]
[/IMG] [IMG]
[/IMG] Self tapping ground screw and star washer. This is what you will need if the ground stud breaks off during removal!
[IMG]
[/IMG] [IMG][IMG]Here are where the chassis ground points are on a C5:



PLEASE let me know if you have any questions. NOTE! All of the pictures that I have of C5 Grounds have been posted on or in this post.
Bill Curlee
updated 02 March 06
Thanks.
Btw, my car is a 1999 C5 Targa (Supercharger ++).
Perhaps not the right forum thread, but while I am in here, does anyone know where to buy the workshop/service manuals? (1999 mod manual sold out in all the shops I visited).
Best regards
Even
My 98 coupe would get the infamous "REDUCED ENGINE POWER", "TRACTION CONTROL FAILURE" and a host of random failure codes. After many, many hours of troubleshooting, replacing the BCM and TAC module, I solved most of the driveability issues. Still getting the random DTC failure codes, I thought that I may be having ground issues. Back in June I cleaned ALL of the chassis grounds and the car virtually stopped throwing the "RANDOM" DTC failure codes. Just moving the wires in the chassis ground connector was enough to change the indications and make the issues stop happening.
I had a chance to speak with some GM C5 Trouble Desk Engineers when I went to Bowling Green KY in April and they pointed out that MANY of the C5 electrical issues can be directly linked to chassis ground problems. The engineer even went as far as to recommending that I chop off the factory under hood chassis ground connectors and combine all of the wires into a single ground lug. Not wanting to just LOP off the factory connector, I took a chance and disassembled one of the ground plug connectors and to my surprise it was indeed full of corroded connections.
I strongly recommend that any C5 owner that has had or who are having electrical issues, examine and clean the chassis ground connectors. This may save you from needlessly replacing expensive electronics modules. Each ground connector can be disassembled and cleaned in about 20 min.
Just cleaning the metal ground connection between the chassis and the plug is only a band aid solution. Now that I look back, when I cleaned my chassis grounds and initially solved my issues, I believe that when the connector is being removed to clean the connection between chassis and the connector, just the wires being moved inside the plug is what changed the indications and made everything work better.
Disassembly of the chassis ground plug and cleaning the contacts inside the connector is the correct method of solving the issue!
I took some pictures of the under hood chassis ground connector and the corrosion that was in it. I cleaned the two connections on the frame rails and the left one was significantly corroded! Taking it apart and cleaning it is a very straight forward procedure and I believe that if you follow this recommendation, you will be on the way to solving the many of the electrical issues.
Here are some detailed pictures of the ground connector and the corrosion that was found inside it!
Picture of under hood Chassis Ground connector G-101

Corrosion inside connector! (You ain't seen nothing yet!)
[IMG]
[/IMG] Next three photos are of the corrosion found on the connector terminals!
[IMG]
[/IMG] [IMG]
[/IMG] [IMG]
[/IMG] Self tapping ground screw and star washer. This is what you will need if the ground stud breaks off during removal!
[IMG]
[/IMG] [IMG][IMG]Here are where the chassis ground points are on a C5:



PLEASE let me know if you have any questions. NOTE! All of the pictures that I have of C5 Grounds have been posted on or in this post.
Bill Curlee
updated 02 March 06
I think I missed a ground on the back of the drivers side cylinder head, in the factory manuals I have it shows a ground there. It looks like it's around the plug for the oil pressure sensor.
Does this ground drop down out of the large harness that runs across the back of the engine?
There is a ground that drops out of the small harness that drops down the drivers side of the engine that goes to the oil temp sensor, is that it?
I let the battery go dead by leaving the lights on accidentally and needed a jump the next day. now all my interior lights light and dash light up when I open either door. Also light up when I turn the key to accessory position. However if I put the key to the run position all interior lights shut off even if I turn the headlights on. Yes the dimmer witch is turned all the way up and work two days ago... any help what it could be?





Check all your DTCs using the DIC and if you have any,, (YOU WILL),, CLEAR ALL of them. See if any return and post that
Report back
BC
The Best of Corvette for Corvette Enthusiasts
The diodes look like zeners but are just regular surface mount diodes.
Fixed it a few months ago and I can leave the car sit for more than a week with no problem. I haven't tried for longer time because it is my daily driver. The only time it sits for more than a weekend is if we go on vacation.
Charlie
Charlie










If your car has a good battery and it depletes the battery in a few days or a week, use a DC Amp meter to measure the battery current draw when the car has entered the BCM sleep mode.
Once ALL of the cars loads are remove (ie doors shut, trunk shut, interior light off, radar detector and phone chargers removed etc, (make sure that you disconnect the under hood light), disconnect the battery NEGATIVE terminal. Connect a DC AMP METER capable of reading at least 10 amps in SERIES with the NEGATIVE battery terminal and the NEGATIVE battery cable. Once you connect the amp meter into the circuit, he car should power up and enter the "SLEEP MODE" with in a few minutes. It should not take longer than 10-15 minutes. If te car is in the RAP (retained acessory power) mode, it may take that entire 10-15 min to power down.


When you initially connect the AMP meter in the circuit, the current draw will be high. Some where around 8 amps. As the BCM determines that the car is secure, it will start dropping off loads and go into the SECURITY MODE and Sleep Mode. As it drops off loads you will see the battery current drop down from 8 amps to around 2-3 amps them in the milliamp range.
If there is a unwanted load, it could take up to 10-15 min for the current reading to settle out as low as it will go. The target reading will be 15-20 milliamperes. As you can see in the next photo, my 02 ZO6 draws .02 or 20 milliamperes.

With this small current draw and a properly charged battery in good condition, your C5 should be able to sit idle (without a battery tender or battery charger) for at least 3 weeks if not longer. My ZO6 has set idle for 30 days and started normally after that period.
C5's that drain batteries in days or a week have an excessive battery current draw issue. Here are a few places that have proven to be a cause of excessive battery current draw:
Drivers or Passengers seat control multifunction switch. The return spring in the switch gets weak or damaged and the seat sticks in a movement position. The motors are thermally protected by a "circuit breaker" in the passengers foot well and will continuously set and trip until the battery goes dead.
Drivers LUMBAR motor. Same as above!

Interior lights, dash lights, or other interior lights.
Head light motor control module. The module can short inside and draw current even though the lights are down and secure. If you feel the module and its HOT, its bad.
Alternator. The diodes can and do go bad. If hey go bad, the field windings will always be powered and draw current. If you suspect that the alternator is drawing current, remove the field terminal wire from the back of the alternator and insert the AMP Meter in SERIES with the circuit (between the red wire and alternator field terminal). The current draw should be ZERO. If you have current draw, one or more diodes are bad in the alternator. The last alternator that I checked this way was drawing 5 amps.
Bose Amplifier. Theres an amp under the dash on the drivers side dash. The relay for that amp sometimes sticks and the amp remains on even though the car is OFF.
Cell phones, radar detectors, wide band controllers ect... can get left plugged in.
NOTE! If you open the door, or trunk or even remove and then replace a fuse for troubleshooting, it will wake the car up and you will need to wait for it to enter the SLEEP mode again to read the current draw.
If you remove a BCM fuse, it will negate the test because the BCM is controlling the current draw.
Hope this helps figure out the reasons for premature battery failure.
Bill Curlee
Any advice or suggestions are greatly appreciated folks.















