For the second day now I have started my car with a message that says decreased engine power, service traction control. It idles very rough and wants to stop. I turn the key to restart and it runs fine but the check engine light is on. After sitting a while and restarting, the check engine light is no longer on and it runs fine. I had the airbox off the other night but I have reconnected everything. Any ideas? Thanks.

 

If the chcek eng light is on there are codes set! Please list the codes here and then erase the ones in memory. Get the car to fail again and list the codes again.

I could guess on what could be wrong but I would rather see the codes before I have you doing wild goose chases!

After you post the codes, more people will chime in on some possible solutions.

Bill C

 

How do I get the codes? I had a '84 Trans-am that I could use a paper clip and count the flashes but I don't have a clue with a C5. Thanks.

 

Welll,,,,,,,,,,,, the paper clip thing is history! Use this procedure:

The IPC display, the 20-character, vacuum florescent screen above the steering column that says "Corvette by Chevrolet" every time you turn on the key, is a powerful device. DIY Service Techs are going to be most interested in the IPC's ability to show diagnostic trouble codes (DTC) for all the modules that transmit them.
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
3. Press and hold "options" and
4. While holding "options", press "fuel" four times within a 10-second period.
Inititially, the on-board diagnostics go into the "automatic" mode which shows each module's DTCs in a pre-set sequence:
· 10 PCM Powertrain Control Module page 6-357 - 6-361
· 28 TCS Traction Control system ABS on page 5-86
· ?? RTD Real Time damping page 3-136 (I do not have this option)
· 40 BCM Body Control Module page 8-405 UTD Page 8-727
· 60 IPC Instrument Panel Cluster page 8-508
· 80 radio page 8-213
· 99 HVAC Heater Vent-Air Conditioning page 1-118
· A0 LDCM Left Door Control module page 8-904 to 8-951
· A1 RDCM Right Door Control Module page 8-904 to 8-951
· AC SCM Seat Control module page 8-1064 -8-1082
· B0 RFA Remote Function Actuation page 8-676
For each module, all DTCs will be displayed. If none are present in a module, you will see "no more codes" on the ICP display.
There are two kinds of DTCs, "Current" and "History," designated with a letter suffix, "C" or "H". A current code indicates that the malfunction is present in the system whose module is displaying data. A history code indicates a problem existed in that module sometime in the last 40 or 50 ignition cycles. When not accompanied by a current code of the same number, it is possible it's evidence of a previous problem, now solved, that was not removed by clearing codes. More likely is that a history code indicates an intermittent malfunction. "Intermittents" are the most challenging DTCs. An intermittent may have happened only once, may have happened more than once but is inconsistent in its appearance or may be happening on a regular basis but not at the time the IPC is displaying codes. History codes can also be caused by a current malfunction in a system that is not operating at the time DTCs are displayed. An example is the rear window defogger which doesn¹t operate until the BCM detects engine rpm. For history codes set by a system 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 IPC has displayed all 11 modules, the system goes into the manual mode which allows selection of each module using combinations of DIC buttons. The manual mode can also be entered at any time during the automatic sequence by pressing any button except "E/M". Once the IPC displays "manual diagnostics," you may select a particular module by pressing the "options" button to go forward or the "trip" button to go back. Once a system is selected and a DTC is displayed, if more than one are present; press "gages" to move 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." Clearing a code does not repair a problem. You are simply erasing the evidence of it in the module's memory.
· 10 PCM Powertrain Control Module page 6-357 - 6-361 Domestic
· A=DTC set immediately and MIL is turned on
· B=MIL turned on after 2 consecutive drive trips
· C=After one failure and stored in History MIL not turned on

Here is another web site that will tell you what the codes are:

This is the absolute best C5 Code web site!!!

http://www.corvettedoctor.com/Codes_Page.htm

Bill Curlee

 

Bill,

Thanks for the procedure. It moves pretty fast but here is what I found.

10 PCM- P1516H
28 TCS- C1226H, C1278H
40 BCM- No codes
58 SDM- No comm.
60 IPC- U1064H, U1016H, U1040H, U1176H
80 Radio- U1016H, U1096H, U1064H
AO LDCM- U1064H
A1 RDCM- U1064H

If I understand correctly, these are history codes except 58. The BCM and PCM were replaced by the previous owner. What do you think? Thanks.

 

Man,,,that's an A$$ load. How old is your battery??? Most of those No Comms and LDCM, RDCM SDM IPC and radio codes happen when your battery is weak and cant keep the proper voltages when you start the car. PLEASE clear the codes and see what ones come back. Those will be the important ones!

BC

 

I'll hit in the a.m. Thanks again.

 

Seeing how the previous owner had to replace the PCM and BCM, It looks like there may have been some more serious problems that the technicians were trying to solve! I had a 98 also and had all of the same codes that you have plus about 15 more. My car was the 98 from HELL! It would strand me on the side of the road frequently without warning!

I had to replace my BCM because it got wet and FRIED! The 97-98 TAC module was known to be problematic and GM sent out a TSB authorizing an up-dated TAC module to take it place.

Other than the TAC module issue, ALL of the other problems were resolved by preforming the chassis ground connector cleaning that is referenced in this post that I made a while back. Oh yea,, I also had a weak battery which caused the no comms and other problems and installed a new OEM gel acid battery. That how I know about those codes!

I strongly recommend reading it and doing the ground connector cleaning procedure. Hell,, it's free and may solve your issues. So far it has helped about 10 other forum members!

Here it is, chech it out:
http://forums.corvetteforum.com/show...al+information

If you have any questions please let me know!

Bill Curlee

 

Okay, I cleared the codes and restarted. The only codes that came back were: 10 PCM- P1516H and 58 SDM- No Comm. Thanks for the link, I'll try the procedure. You mentioned more serious problems. Might I be in for some? Thanks.

 

P1516 is the only code right that I am concerned with right now. This code is sometimes difficult to fix. I had a 98 coupe and the TAC module was a KNOWN GM problem! When this problem occured the cure was to install an updated TAC module.

Before you spend $208 plus shipping I would like you to see if doing the simple/free repairs will take care of the problem.
Please accomplish the following repairs:

1. Clean the throttle blade and throttle bore with carb cleaner. Pay attention to the back of the blade.

2. Check the electrical connections at the throttle body and make sure that thet are clean and tight.

3. There is a fuel rail support on the drivers side of the engine near the back of the manifold. It suooprts the rear of the fuel rail. The verticle metal support is sharp and the wiring harness for the engine wraps around it. That brace sometime cuts the wires and causes all sorts of probems. See if any of your wires are compromised.

4. Clean all of the under hood chassis grounds. Please review this post that I wrote and let me know if you have any questions.

http://forums.corvetteforum.com/show...al+information

When all of that is done, fire her up and let me know if we made any progress.

Bill C

 

Will do. Thanks.

 

Bill,

I got a little carried away with your tip about the corrosion and forgot about the throttle blade etc..., however all codes except the No Comm. are gone. I pulled the ground connectors by the lights and found no evidence of corrosion. I blew them out and reassembled them and the codes are gone. Things don't tend to work out like this. I know it's not over yet. Should I do the other procedures even though there are no codes? Thanks.