It seems like I only post on the forum when things go wrong, but that's another story.

My brother-inlaw has a '01 that decided to just die on him the other day. After pulling into the gas station, he couldn't get the car to start up. It cranks, but it won't start. The car was eventually towed to the house.

Here are the list of things that we did in no particular order.

- Fuel pump does not prime on it's own
- No fuel pressure at the schrader valve( it will initially squirt out a drop and then stops)
- The fuel pump will prime if we jump the relay
- FP ground wire checked out fine near the rear tire.
- Grounds near the headlights are good, no corrosion.
- Harness under the driver seat checked
- Harness at the pass. door checked.
- Harness at the PCM(pass. fender) checked

All of the codes start with "U" so I'm assuming that the PCM is not functioning correctly.

How do I go about testing the PCM? Any advice would be greatly appreciated.

Thanks!

 

Examine the wiring harness connections that are beside and under the battery for acid damage. A list of the code numbers would also be helpful in trouble shooting your problem.

 

Did you check the Crank Position sensor. Turn the key on does the fuel pump run 5 to 10 seconds? If not no power to pump. IF yes the pump runs but the signal from the CPS must get to the CPU to tell the computer the engine is running to keep the fuel pump on. IF the CPS is bad the car will turn over with the starter but not fire.

 

We only did a visual check on the CPS and it looked fine. We knew that it was something electrical b/c the FP would not prime unless we put a jumper on the relay.

After about 5-6hrs of trying to trace down the problem, my brother, my brother-inlaw, and I decided to clean up and put everything back together. We were planning to order a used PCM to test it out so as we were about to push the car back up the driveway, my brother-inlaw decided to give it one last shot. Out of nowhere the freaking car decides to start. We were excited and happy to hear the engine roar, but at the same time, we're still stumped as to what the actual cause was.

For now, the car is running like normal and hopefully, it stays this way.

 

I never seen a PCM go bad that wasn't caused by an electrical short by somebody grounding something they shouldn't have or a nasty wiring job somewhere else in the car.

 

You never did post all the DTCs that you had. That would have been a good start. What U series codes did you have?/

Did you have any NO COMMS DIC messages when you read the DTCs??

Bill

 

I'm sorry, but I don't have the codes with me. There were about 8-10 codes all starting with U. My brother-inlaw lives about an hour away from me, but he's the one that has it all written down. I remember the first round, the codes were a series of U10xx and the second round after the battery was disconnected, the codes were a series of U13xx.
I know that these aren't specific, but I can't recall all the codes at the moment.

"Reduce engine power" and "Low Fuel" were the two messages that keep popping up.

 

OK,,,, You added more clues and that gives me an idea, You had or are still having issues with the BCM or the serial data buss..

Something is corrupting the buss and it could be moisture in the BCM or loose/spread/damaged female pins in the seat connector or LDCM / RDCM door connectors.

You really need a spare male pin to make sure that each female pin grips the male pin tightly.

Bill

 

Late last night, the car died on my brother-inlaw again. While stranded on the side of the road, he decided to reset the PCM by pulling on the fuse to no avail.

I had a chance to look at the car today and tried to pull the codes, but nothing is popping up. It shows "No Command" for everything. It's still flashing reduce engine power and low fuel.

The fuel pump does not prime, but there's a buzzing sound coming from the engine bay while the key is in the ON position. Is this normal? I don't see the car often and I've never really paid attention to this before.

I double checked all the wires again: under the seat, at the pass. door, and everything looks clean. There's no obvious corrosion, moisture, or dirt that I could see.

I don't understand why the codes are not showing up. I think when he reset the PCM is cleared everything, but shouldn't the codes pop up again.

Any thoughts?

 

I think you meant to write the DTCs say NO COMMUNICATIONS. If so,,, You have an issue on the serial data buss,, plain and simple.

Look in the passengers foot well to the LEFT of the BCM. You will see two small thin connectors. One of them has FOUR wires. Remove the top shorting strip from the connector and see if your issue goes away.





Start the engine and test.. You will have NO COMMS on the LDCM, RDCM and SCM But,,,,,,,, the engine should start and run if the issue is on any one of those modules.

Bill

 

Bill

I removed the connector as suggested and the car did not start. I still do not hear the fuel pump prime. What should I look for next?

Thank you so much for taking the time to guide us through this.

 

Read the DTCs again using the DIC. If there are a TON, clear them and attempt to start the car. DO NOT turn off the ignition and read the DTCs

Post what you get.


Here is the procedure:

READING YOUR Engine Diagnostic Codes (DTCs)
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 etc…)
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.

Here is very good site of DTC definitions:


http://www.gearchatter.com


Make sure to include the H or C suffix!!

 

Bill

I did that right afterwards and it still says no communication.

 

What modules have NO COMMS????????

No Comms can also be caused by the module not receiving full power or no power. You need to find ALL the BCM and PCM fuses ( there are NUMEROUS BCM and PCM fuses. and check them. You first need to see if they are blown. Then you need to measure the voltage on each fuse to GROUND. Make SURE that the Ignition switch is ON cause some fuses are only powered when the ignition is ON. Each fuse MUST have FULL battery voltage on it. If you find one that has significantly less than full battery voltage, thats a problem!


Examine this post. Its where Im heading next. It list the fuses that you should check.....

http://forums.corvetteforum.com/c5-t...ch-repair.html
Bill

 

Also check the voltage on the fuel pump fuse!

BC

 

All the modules read NO COMMS. I will look into checking all the fuses.

 

Bill, here's what I got from the test.

Here are the fuses powered by the "HOT in ACC and ON". part of the switch:

Ok,,,here are the fuses that your going to check:

Under Hood Fuse Center

ENG ING1 FUSE# 19 - No voltage

INJR 2 FUSE# 18 - Good



THROTCONT FUSE# 17 - No voltage



INJR 1 FUSE# 22 - Good



PCM FUSE# 16 - No voltage



F/PMP FUSE# 13 - No voltage



Instrument Panel Fuse block

BTSI BU Fuse# 21 - No voltage


BCM 13 Fuse# 22 - Fuse not present

IPC Fuse# 19 - No voltage

 

IGNITION SWITCH!!!!!!!!!!!!!!! Check it Clean it, or replace it..

 

Fingers crossed, eyes crossed, and toes crossed. I hope that this is the culprit. I will order the part and replace it. Thank you again!!!

 

The AC Delco ignition switch came in today in the mail. I installed it and put everything back together and it's doing the same thing.

The fuel pump isn't priming, reduce engine power, and low fuel is showing. "NO COMMS" on all modules.

I switch the relays on the FP and it's still not coming on. I'm determined to fix this myself and not have him take it to the stealership.

Any thoughts Bill?