Possible failing ECM or PROM
Thread Starter
Instructor
Joined: Mar 2010
Posts: 130
Likes: 2
From: Saint Louis MO
Possible failing ECM or PROM
I originally posted this in the "scan and tune" area, but I think that was the wrong place...
I have a 92 automatic coupe, that seemingly runs fine. I recently bought an EQUUS 3140 OBD-I capable scanner for use on the several OBD-I cars I have access to and work on.
With all of these cars, the scan data is extremely easy to obtain (pops up in seconds), EXCEPT for the 92...
When I plug in the reader, key on, engine off, it takes about 5 minutes for the device to pull any data. Here is what I got today:
First try: After about 5 minutes, got message that scanner could not communicate with car
Second try: After about 5 minutes, got several codes:
DTC 51 PROM error
DTC 63 Right O2 sensor error
DTC 62 Oil temp sensor high
DTC 69 A/C clutch circuit open
DTC 68 A/C relay shorted
DTC 67 A/C press. transducer degraded
DTC 64 Right O2 sensor lean
Third try:
DTC 63 Right O2 error
DTC 72 Gear switch fault
DTC 71 A/C evap. temp. sensor fail
Fourth try:
DTC 51 PROM Error
DTC 63, 69, 68, 67 ,64
Needless to say, none of these things appear to be wrong with the car...
Given the long time it took for the communication to occur, and the DTC 51 PROM error code, I suspect the computer is somehow failing...
Anyone have ideas on what is going on, and what do I need to do to fix?
Thanks for the help!
-David
I have a 92 automatic coupe, that seemingly runs fine. I recently bought an EQUUS 3140 OBD-I capable scanner for use on the several OBD-I cars I have access to and work on.
With all of these cars, the scan data is extremely easy to obtain (pops up in seconds), EXCEPT for the 92...
When I plug in the reader, key on, engine off, it takes about 5 minutes for the device to pull any data. Here is what I got today:
First try: After about 5 minutes, got message that scanner could not communicate with car
Second try: After about 5 minutes, got several codes:
DTC 51 PROM error
DTC 63 Right O2 sensor error
DTC 62 Oil temp sensor high
DTC 69 A/C clutch circuit open
DTC 68 A/C relay shorted
DTC 67 A/C press. transducer degraded
DTC 64 Right O2 sensor lean
Third try:
DTC 63 Right O2 error
DTC 72 Gear switch fault
DTC 71 A/C evap. temp. sensor fail
Fourth try:
DTC 51 PROM Error
DTC 63, 69, 68, 67 ,64
Needless to say, none of these things appear to be wrong with the car...
Given the long time it took for the communication to occur, and the DTC 51 PROM error code, I suspect the computer is somehow failing...
Anyone have ideas on what is going on, and what do I need to do to fix?
Thanks for the help!
-David
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
I originally posted this in the "scan and tune" area, but I think that was the wrong place...
I have a 92 automatic coupe, that seemingly runs fine. I recently bought an EQUUS 3140 OBD-I capable scanner for use on the several OBD-I cars I have access to and work on.
With all of these cars, the scan data is extremely easy to obtain (pops up in seconds), EXCEPT for the 92...
When I plug in the reader, key on, engine off, it takes about 5 minutes for the device to pull any data. Here is what I got today:
First try: After about 5 minutes, got message that scanner could not communicate with car
Second try: After about 5 minutes, got several codes:
DTC 51 PROM error
DTC 63 Right O2 sensor error
DTC 62 Oil temp sensor high
DTC 69 A/C clutch circuit open
DTC 68 A/C relay shorted
DTC 67 A/C press. transducer degraded
DTC 64 Right O2 sensor lean
Third try:
DTC 63 Right O2 error
DTC 72 Gear switch fault
DTC 71 A/C evap. temp. sensor fail
Fourth try:
DTC 51 PROM Error
DTC 63, 69, 68, 67 ,64
Needless to say, none of these things appear to be wrong with the car...
Given the long time it took for the communication to occur, and the DTC 51 PROM error code, I suspect the computer is somehow failing...
Anyone have ideas on what is going on, and what do I need to do to fix?
Thanks for the help!
-David
I have a 92 automatic coupe, that seemingly runs fine. I recently bought an EQUUS 3140 OBD-I capable scanner for use on the several OBD-I cars I have access to and work on.
With all of these cars, the scan data is extremely easy to obtain (pops up in seconds), EXCEPT for the 92...
When I plug in the reader, key on, engine off, it takes about 5 minutes for the device to pull any data. Here is what I got today:
First try: After about 5 minutes, got message that scanner could not communicate with car
Second try: After about 5 minutes, got several codes:
DTC 51 PROM error
DTC 63 Right O2 sensor error
DTC 62 Oil temp sensor high
DTC 69 A/C clutch circuit open
DTC 68 A/C relay shorted
DTC 67 A/C press. transducer degraded
DTC 64 Right O2 sensor lean
Third try:
DTC 63 Right O2 error
DTC 72 Gear switch fault
DTC 71 A/C evap. temp. sensor fail
Fourth try:
DTC 51 PROM Error
DTC 63, 69, 68, 67 ,64
Needless to say, none of these things appear to be wrong with the car...
Given the long time it took for the communication to occur, and the DTC 51 PROM error code, I suspect the computer is somehow failing...
Anyone have ideas on what is going on, and what do I need to do to fix?
Thanks for the help!
-David
Like you at first I assumed the issue was a problem with the car and went through all the steps to verify continuity from the ALDL to the ECM etc.no luck at all doing that. I eventually tried the scan tool on another 93 that was running normally with no codes and the tool would not work on it either.
At that point I contacted customer support for the tool and explained the issue, they sent me a new cable, it failed to fix the problem so I contacted them again. The second time they sent a new scanner, it too failed to function so I again called back explaining that I had purchased the tool specifically to use on the 93 and if it would not function I wanted to return the tool for a refund. They said they would send a third tool to try and miraculously that one has functioned perfectly.
My point is that the 92-93 ECM's seem to be somewhat unique and that the issue may be a communication problem with the tool. I have a spare PROM that you can try if needed, but suggest you first try a different scan tool, good luck.
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
I don't have any experience with the above mentioned aftermarket scan tools.
But I know for a fact that Snap On brand scanners have the option for you to reconfigure the Baud Communication rate.
Done with the soft touch entry pads.
Or on the old Red Brick MT2500 like I have at home here, with the buttons & scroll wheel.
That old Red Brick Scanner works pretty good on most anything ever made domestic & foreign.
Seldom ever have to reconfigure the Baud communication rate to match a vehicle.
Does it automatic for you I suspect.
But the option is there on the setup menus.
Have not tried mine on a 1992 Vette.
Be glad to try it on yours if every nearby me.
Brian
But I know for a fact that Snap On brand scanners have the option for you to reconfigure the Baud Communication rate.
Done with the soft touch entry pads.
Or on the old Red Brick MT2500 like I have at home here, with the buttons & scroll wheel.
That old Red Brick Scanner works pretty good on most anything ever made domestic & foreign.
Seldom ever have to reconfigure the Baud communication rate to match a vehicle.
Does it automatic for you I suspect.
But the option is there on the setup menus.
Have not tried mine on a 1992 Vette.
Be glad to try it on yours if every nearby me.
Brian
Thread Starter
Instructor
Joined: Mar 2010
Posts: 130
Likes: 2
From: Saint Louis MO
Is there a paperclip method I can use on a 92 to get the codes to blink on the dash?
I used that on the other cars before I bought the scan tool. How can you do that with the 92 by connecting pins on the ALDL together?
Figure that might be a good double check...
-David
I used that on the other cars before I bought the scan tool. How can you do that with the 92 by connecting pins on the ALDL together?
Figure that might be a good double check...
-David
Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Pulling Codes Revisited
________________________________________
ALDL 201 (OBD I)
1981 Corvette (L81) models have a very simple computerised ignition timing system. There is very little diagnostic information available with these cars. The GM shop manual is recommended for this vehicle. The ALDL connector is under the centre console ash tray.
1982 Corvette (L83 Crossfire) models had a more detailed ECM, much like later vehicles. The location of the ALDL connector is under the centre console ash tray. The diagnosis is more simplified, but similar to later vehicles.
From 1984 until the end of the 1993 model year a 12 pin ALDL was used. After that, a 16 pin ALDL connector was used. The 1994 and 1995 model year still used the OBD-I system even though they have 16 pin connectors. The 16 pin connector in the 1996 C4 is used for the much more complex OBD-II system and a scan tool is required to discover the OBD-II system's secrets.
For the '84- end of '93, 12 pins:
Pin "B" is the diagnostic enable pin and pin "A" is ground. Grounding pin "B" to enable the diagnostic readout of the ECM/PCM.
To recover the codes, short pins "A" and "B" together using a small section of electrical wire or paper clip.
With the ignition turned OFF, short pins "A" and "B" on the ALDL.
Turn IGN ON (but not to RUN).
The "Check Engine" light (early C4s) or "SYS" light (later C4s) will flash a Code 12 (a single flash followed by two flashes) and will repeat three times (Flash (pause) Flash Flash (long pause), Flash (pause) Flash Flash (long pause), Flash (pause) Flash Flash (long pause).
Code 12 is a delimiter or marker code to show where the error code string begins and ends.
After the three Code 12 flashes, you will either get an error code (or codes) or you will get another string of Code 12 flashes if there are no trouble codes stored.
All codes are repeated three times with a long pause between each code group (36 or Flash Flash Flash pause followed by six flashes, repeated three times, folowed by a long pause with any additional codes stored then flashed).
The "Check Engine/System" light on with engine running means the condition(s) are currently present. If the light is not on during RUN operation, the limits were exceeded at some point in time and the event was recorded in memory, but the reading has since returned to the normal operating range.
Remember to remove the shorting device from the connector after you have read the codes.
Clearing the Codes
To clear the codes from memory, remove the negative battery cable for a minimum of 10 seconds.
Disconnecting the battery will clear all stored codes and and any stored memory (radio button presets, clock, trip odometer, average gas mileage memory, power seats). Your ECM/PCM computer will also have to relearn timing/mixture/exhaust emissions.
Make absolutely certain the ignition key is turned OFF. If you connect the battery with the ignition switch ON, you can destroy the ECM/PCM module.
For 1994 and later models, you will need to recover the codes using a special procedure involving the speedometer and the odometer as explained in the service manual or use a special diagnostic device known as a scan tool.
For the '94 - '95, 16 pins (but still OBD I):
Beginning in 1994, you short pin "12" to pin "4" and once again turn the ignition switch to "On" without starting the engine.
The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:
Module "1" is still the CCM module.
Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.
Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).
Module 9 is the ABS/ASR module number from 1994 through 1996.
Finally, Module "A", the DERM (Dynamic Energy Control Module --- the air bag control module) will be requested to show any codes.
Just like the 1990-1993 display, you read the codes on the speedometer and read the module number on the trip odometer.
Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on.
Turn the ignition off and remove the short to restore normal operation.
1996 to 2004 Corvette (OBD II):
Turn IGN ON, ENG OFF.
ON DIC, Press RESET button to clear any warning messages.
Press and hold OPTIONS.
While holding OPTIONS, press FUEL four times within 10 sec.
Go into an AUTOMATIC mode to shows all parameters: PCM-TCS-RTD-BCM-IPC-RADIO-HVAC-LDCM-RDCM-SCM-RFA. If there are no problems, you will see "NO MORE CODES" on the ICP display.
The computer displays two kinds of codes, CURRENT and HISTORY, designated "C" or "H". A CURRENT code indicates a malfunction is present in the system whose module is displaying data. A HISTORY code indicates a past problem.
When the screen displays MANUAL DIAGNOSTICS, select the desired module by pressing the OPTIONS button to go forward or the TRIP button to go back. Press GAUGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase or CLEAR codes, press RESET.
________________________________________
ALDL 201 (OBD I)
1981 Corvette (L81) models have a very simple computerised ignition timing system. There is very little diagnostic information available with these cars. The GM shop manual is recommended for this vehicle. The ALDL connector is under the centre console ash tray.
1982 Corvette (L83 Crossfire) models had a more detailed ECM, much like later vehicles. The location of the ALDL connector is under the centre console ash tray. The diagnosis is more simplified, but similar to later vehicles.
From 1984 until the end of the 1993 model year a 12 pin ALDL was used. After that, a 16 pin ALDL connector was used. The 1994 and 1995 model year still used the OBD-I system even though they have 16 pin connectors. The 16 pin connector in the 1996 C4 is used for the much more complex OBD-II system and a scan tool is required to discover the OBD-II system's secrets.
For the '84- end of '93, 12 pins:
Pin "B" is the diagnostic enable pin and pin "A" is ground. Grounding pin "B" to enable the diagnostic readout of the ECM/PCM.
To recover the codes, short pins "A" and "B" together using a small section of electrical wire or paper clip.
With the ignition turned OFF, short pins "A" and "B" on the ALDL.
Turn IGN ON (but not to RUN).
The "Check Engine" light (early C4s) or "SYS" light (later C4s) will flash a Code 12 (a single flash followed by two flashes) and will repeat three times (Flash (pause) Flash Flash (long pause), Flash (pause) Flash Flash (long pause), Flash (pause) Flash Flash (long pause).
Code 12 is a delimiter or marker code to show where the error code string begins and ends.
After the three Code 12 flashes, you will either get an error code (or codes) or you will get another string of Code 12 flashes if there are no trouble codes stored.
All codes are repeated three times with a long pause between each code group (36 or Flash Flash Flash pause followed by six flashes, repeated three times, folowed by a long pause with any additional codes stored then flashed).
The "Check Engine/System" light on with engine running means the condition(s) are currently present. If the light is not on during RUN operation, the limits were exceeded at some point in time and the event was recorded in memory, but the reading has since returned to the normal operating range.
Remember to remove the shorting device from the connector after you have read the codes.
Clearing the Codes
To clear the codes from memory, remove the negative battery cable for a minimum of 10 seconds.
Disconnecting the battery will clear all stored codes and and any stored memory (radio button presets, clock, trip odometer, average gas mileage memory, power seats). Your ECM/PCM computer will also have to relearn timing/mixture/exhaust emissions.
Make absolutely certain the ignition key is turned OFF. If you connect the battery with the ignition switch ON, you can destroy the ECM/PCM module.
For 1994 and later models, you will need to recover the codes using a special procedure involving the speedometer and the odometer as explained in the service manual or use a special diagnostic device known as a scan tool.
For the '94 - '95, 16 pins (but still OBD I):
Beginning in 1994, you short pin "12" to pin "4" and once again turn the ignition switch to "On" without starting the engine.
The speedometer will display any codes using the same protocol as the 1990-1993 model but there are some changes in the designation for the modules plus additional modules are added:
Module "1" is still the CCM module.
Module "4" is now called the PCM module (Powertrain Control Module) because automatic transmission computer control was added to Engine Control Module in 1994.
Module 7 (on the 1996 model only) is the RTD module. (This is the Real Time Dampening module which replaced the Selective Ride Control module in 1996).
Module 9 is the ABS/ASR module number from 1994 through 1996.
Finally, Module "A", the DERM (Dynamic Energy Control Module --- the air bag control module) will be requested to show any codes.
Just like the 1990-1993 display, you read the codes on the speedometer and read the module number on the trip odometer.
Again, you can cause the codes to repeat by turning the ignition off for five seconds and then back on.
Turn the ignition off and remove the short to restore normal operation.
1996 to 2004 Corvette (OBD II):
Turn IGN ON, ENG OFF.
ON DIC, Press RESET button to clear any warning messages.
Press and hold OPTIONS.
While holding OPTIONS, press FUEL four times within 10 sec.
Go into an AUTOMATIC mode to shows all parameters: PCM-TCS-RTD-BCM-IPC-RADIO-HVAC-LDCM-RDCM-SCM-RFA. If there are no problems, you will see "NO MORE CODES" on the ICP display.
The computer displays two kinds of codes, CURRENT and HISTORY, designated "C" or "H". A CURRENT code indicates a malfunction is present in the system whose module is displaying data. A HISTORY code indicates a past problem.
When the screen displays MANUAL DIAGNOSTICS, select the desired module by pressing the OPTIONS button to go forward or the TRIP button to go back. Press GAUGES to go forward or FUEL to go back.
To exit the diagnostic mode at any time, press E/M. If you want to erase or CLEAR codes, press RESET.
Thread Starter
Instructor
Joined: Mar 2010
Posts: 130
Likes: 2
From: Saint Louis MO
Ok, looks like we have an incompatibility issue...
When I did the "shorting A&B" method on the ALDL, the only code I get is13, which relates to the O2 sensors...
Considering the device I have doesn't work correctly with this car, can anyone suggest a better OBD-I reader for use with it?
What about the Snap-On MT2500 mentioned earlier? Does it work, and does it display any live data when the car is running?
The device I have now only displays codes on OBD-I cars - no live data.
Any suggestions regarding the Snap-On product, and what I need to ensure it has with it if I buy one from ebay, etc.
When I did the "shorting A&B" method on the ALDL, the only code I get is13, which relates to the O2 sensors...
Considering the device I have doesn't work correctly with this car, can anyone suggest a better OBD-I reader for use with it?
What about the Snap-On MT2500 mentioned earlier? Does it work, and does it display any live data when the car is running?
The device I have now only displays codes on OBD-I cars - no live data.
Any suggestions regarding the Snap-On product, and what I need to ensure it has with it if I buy one from ebay, etc.
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
[QUOTE=daveshea;1578908003]Ok, looks like we have an incompatibility issue...
When I did the "shorting A&B" method on the ALDL, the only code I get is13, which relates to the O2 sensors...
Considering the device I have doesn't work correctly with this car, can anyone suggest a better OBD-I reader for use with it?
What about the Snap-On MT2500 mentioned earlier? Does it work, and does it display any live data when the car is running?
The device I have now only displays codes on OBD-I cars - no live data.
Any suggestions regarding the Snap-On product, and what I need to ensure it has with it if I buy one from ebay, etc.[/QUO
I bought my MT2500 Snap On Scanner from a retired auto mechanic.
"Ask the Seller " option off to the right hand side of that ebay screen showing the item you are interested is a powerful tool.
If they don't answer my question(s) within 24 hours, I usually pass on the item.
You need operating software to operate any true auto scanner,
they are non functional without them.
Be sure to get the latest operating software cartridges if all possible.
The last releases of the MT2500 software cartridges were reprogrammable units.
Black in color.
Some of the older software releases are very useful yet I have found.
Has live data elements shown that the later software deletes for my 87 Vert C4.
I think for more operating system storage room in the later software version.
Also a trouble shooter cartridge that goes with these old Snap On MT2500 scanners.
Have to be at the right place at the right time like I was.
Landed 2005 main operating software, 2005 troubleshooter latest updates till they quit building the MT2500 model,
older software cartridges going back to 1987 production build dates.
The scanner body of the old MT2500's is only worth $100 to $200 tops.
The operating software & troubleshooter software is Gold.
2005 versions each sell for $400 to $600 on ebay.
I landed everything For around $150 during lunchtime back in November 2007.
Just when the US Recessions started.
Watch ebay.
Never know what will show up & you can claim as yours for very low cost.
BR
When I did the "shorting A&B" method on the ALDL, the only code I get is13, which relates to the O2 sensors...
Considering the device I have doesn't work correctly with this car, can anyone suggest a better OBD-I reader for use with it?
What about the Snap-On MT2500 mentioned earlier? Does it work, and does it display any live data when the car is running?
The device I have now only displays codes on OBD-I cars - no live data.
Any suggestions regarding the Snap-On product, and what I need to ensure it has with it if I buy one from ebay, etc.[/QUO
I bought my MT2500 Snap On Scanner from a retired auto mechanic.
"Ask the Seller " option off to the right hand side of that ebay screen showing the item you are interested is a powerful tool.
If they don't answer my question(s) within 24 hours, I usually pass on the item.
You need operating software to operate any true auto scanner,
they are non functional without them.
Be sure to get the latest operating software cartridges if all possible.
The last releases of the MT2500 software cartridges were reprogrammable units.
Black in color.
Some of the older software releases are very useful yet I have found.
Has live data elements shown that the later software deletes for my 87 Vert C4.
I think for more operating system storage room in the later software version.
Also a trouble shooter cartridge that goes with these old Snap On MT2500 scanners.
Have to be at the right place at the right time like I was.
Landed 2005 main operating software, 2005 troubleshooter latest updates till they quit building the MT2500 model,
older software cartridges going back to 1987 production build dates.
The scanner body of the old MT2500's is only worth $100 to $200 tops.
The operating software & troubleshooter software is Gold.
2005 versions each sell for $400 to $600 on ebay.
I landed everything For around $150 during lunchtime back in November 2007.
Just when the US Recessions started.
Watch ebay.
Never know what will show up & you can claim as yours for very low cost.
BR
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
I.E.>
Real Bad Economic News,
World Coming to an End,
Armageddon,
ect,
Is a really good time to Buy off of ebay I have found.
Others are glued to the TV screen or Facebook, Corvette Forum...
Not me,
I won that item $ cheep again.
Real Bad Economic News,
World Coming to an End,
Armageddon,
ect,
Is a really good time to Buy off of ebay I have found.
Others are glued to the TV screen or Facebook, Corvette Forum...
Not me,
I won that item $ cheep again.
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Safety Car
Joined: Jun 2006
Posts: 3,629
Likes: 28
From: FL
Another option easily found on ebay is a used Tech1 by Vetronix. It was the dedicated dealer scan tool used when C4's were state of the art, long ago replaced in dealerships by newer versions.
Far superior to nearly all consumer grade scan tools, it offers bidirectional function and the ability to access all of the C4 modules including CCM, ABS, FX3 etc. Such functions are usually only available on professional grade tools such as the Snap-on mentioned or higher end OTC tools which often cost far more.
Try to find one with the Mass Storage cartridge and it will handle any C4 diagnostic function, prices run between 200 and 500 dollars depending on what accessories are included. Adding a VIM module will even allow use on OBDII vehicles, cartridges are also available that will service other domestic and foreign vehicles.
Far superior to nearly all consumer grade scan tools, it offers bidirectional function and the ability to access all of the C4 modules including CCM, ABS, FX3 etc. Such functions are usually only available on professional grade tools such as the Snap-on mentioned or higher end OTC tools which often cost far more.
Try to find one with the Mass Storage cartridge and it will handle any C4 diagnostic function, prices run between 200 and 500 dollars depending on what accessories are included. Adding a VIM module will even allow use on OBDII vehicles, cartridges are also available that will service other domestic and foreign vehicles.
Last edited by toptechx6; Oct 9, 2011 at 07:18 AM. Reason: added info
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
Programmable Read Only Memory. The program that your ECM runs is stored in it.
EPROM = Erasable Programmable Read Only Memory.
EEPROM = Electrically Erasable Programmable Read Only Memory
EPROMs must be erased with UV light. The whole thing must be erased and the whole thing must be reprogrammed, even to change just one byte.
EEPROMs can be changed by sending a modified file to the PCM.
EPROM = Erasable Programmable Read Only Memory.
EEPROM = Electrically Erasable Programmable Read Only Memory
EPROMs must be erased with UV light. The whole thing must be erased and the whole thing must be reprogrammed, even to change just one byte.
EEPROMs can be changed by sending a modified file to the PCM.
Last edited by Cliff Harris; Oct 13, 2015 at 11:59 PM. Reason: Added clarification.
Melting Slicks
Joined: Nov 2013
Posts: 3,451
Likes: 336
From: Greater Cincinnati Area.
