Calebxmaxx

Hi all,

I’ve owned this car for about a month now and have driven it a total of about 1 hour. I’ve had nothing but electrical issues since purchase. I didn’t do my research on C5’s before purchasing, I just knew they looked great and I wanted one! With that being said, I haven’t been scared of working on it. Just trying to get it all lined out and I’ve ran into a road block. I’ve spent hours on this site searching and need some help.

A little history with the car. When I purchased it, the temp sensor would go straight to red and the fuel gauge straight to empty and the fuel pump would cycle on and off so much that the car wouldn’t stay running. After hours of research, replacing the ignition switch and lock cylinder, also a new key, the car was running great. Drove it around 100 miles when I started having the issue I am now.

On my way home I noticed the temperature gauge start fluctuating and then go to red, overtemp came on DIC, reduced engine power, and check gauges, then the oil pressure went to 80 psi. At this point I pulled the car into a parking lot and shut it off. Popped the hood and no signs of overheating, I’m convinced at this point it’s electrical, as the gauge was at 180ish and just went to 260 really fast and the started bouncing around. I check the codes and got a low temp voltage code, a fuel level sensor high voltage code. At this point I reset the codes and started to ease back to my buddy’s house that I had just left, at this time the fuel gauge went from 3/4 straight to empty. So now I’m really convinced it’s an electrical issue. Could it be the new ignition switch I just replaced? The grounds up front by headlights are clean, battery ground is clean with a new battery reading good voltage. If anyone has had this issue before let me know.

mmartinez

Many c5 owners have had the same issues, it still could be your ignition switch not sending the correct voltage to the sensors. Many people experience bad readings caused by the individual sensors, flakey water temperature sending unit, oil pressure sending unit, and lastly your gas gauge suddenly going to empty could very well be deposits on the fuel tank sending units which most times can be corrected by a couple of treatments of Techron fuel system concentrate. Good luck, and welcome to C5 ownership.

GCG

Just trying to get the whole picture. Why did you have to replace the key cylinder when you installed a new ignition switch? Was it damaged?

Since this car is new to you, let me just add a couple of things that won't hurt and definitely will allow you to scratch them from the potential issues list.

As you may know, this car is a "bottom feeder" and in time, the amount of debris that accumulates in the space between the a/c condenser and the radiator will surprise you. Remove the radiator upper cover/support, take a look and try to clean as much as you can using a water hose. Direct it's flow through the fins, from behind towards the front. Search the forum for more details.

Since you're struggling with electrical issues, it's important to make sure the electrical system is performing well. Using a multimeter check the battery voltage directly at the battery posts. A fully charged battery should be above 12.6v. If it is not, I suggest you take it out, charge it and take it an auto parts store to have it load-tested.

It would also be good to check voltage directly at the battery posts with the engine running. It should be between 13.5v and 14.5v give or take.

It's also important to determine the voltage drop between the alternator and battery. With the engine running, place the multimeter's (+) lead on the alternator's output stud and the multimeter's (-) lead on the battery's (+) post. Ideally it should read 0v, but in practice it shouldn't be more than a couple of tenths of a volt. If it is more, the "alternator-starter solenoid-battery" chain needs to be checked. Check, clean and tight connections at the starter solenoid and retest the voltage drop.

Do the easy, basic stuff first and then reassess your position

Bill Curlee

The gages do not get their readings directly off of the sensors. They ALL get the readings through the BCM. All of the signals are transmitted through the SERIAL DATA BUSS as digital data. The BCM is like a router for ALL the other modules.

NOTE: The DC Voltmeter reads directly off the ignition switch output voltage.

If you have MULTIPLE gage reading issues, something is wrong with the BCM or serial data that is being fed to the IPC.

C5 modules have multiple power inputs. Most have TWO power sources: Hot at all times "BATTERY BUSS Powered" and Hot in ignition ON/RUN "Ignition Switch powered" The BCM has something like 5 seperate DC power inputs. You need to actually measure the two test points on top of each module fuse to chassis ground to see if the module is getting full battery voltage .

The BCM does NOT like water or moisture!! See if the carpet or underlayment in the passengers foot well is wet or damp or if the BCM is wet.

There is also a C5 issue where other modules can corrupt the serial data buss. Next to the BCM (to the left of it) are two thin STAR connectors (STAR-1 & STAR-2) Find the one with FOUR wires and pop the top shorting buss off of the connector and see if the craziness goes away.

Bill

Calebxmaxx

I appreciate everyone’s input. I replaced lock cylinder because it was worn and causing the security system to act up. The car is at my buddy’s house (who is a certified mechanic) and he’s been going over everything y’all have suggested. He said that he checked out everything yesterday y’all mentioned and didn’t find anything. The only thing he said that he found was the PCM appeared to only be getting 12v to it while everything else he checked out was getting right at 13v ie BCM. He took the BCM out and the only thing he noticed was a small spot of corrosion in one corner that he cleaned and no difference was made. He’s thinking possibly wiring leading up to PCM under battery or PCM itself. We both work at FD and he’s going to look more into that tomorrow when we get off.

gpd132

Its a very frustrating experience. You will never get satisfaction with it. Don't spend too much money trying to fix it. Something else will fail guaranteed. Unload it before you go broke.

Calebxmaxx

As frustrating as it may get at times, I don’t feel like giving up on it. It seems to be a minor problem, just have to figure out where that problem is.

Calebxmaxx

We are going to pull the battery today and inspect all of the wiring up under there, and most likely pull the PCM, check and clean all of the connectors and see what results we get.

GUSTO14

Welcome to the Corvette Forum. I believe you will soon find it to be the most valuable tool in your tool box.

You didn't mention the mileage on your car, it could be useful information for getting more relevant feedback.

One thing thing not mentioned yet is to check the grounds around the car. At you cars' age it is worth checking that they are all making good contact between the various wires and the chassis.


Good luck... GUSTO

Calebxmaxx

Thanks for the feedback, so far have only checked/cleaned #7, #8 and #9. Will get to the others. My car has 127k miles on it. It was definitely used and not sat up in a garage it’s whole life.

GUSTO14

My view is that one of the most significant weaknesses of the C5 (as well as many modern vehicles) is their increasing reliance on hundreds of electrical relay's, many of them micro-relays. These relays control the myriad of electrical tasks that the car must perform to function properly. Relay's abhor moisture and humidity.

As these cars age and spend more and more time outside in the environment, humidity will take its toll on them.

Good luck and persevere... GUSTO

Calebxmaxx

So after removing the battery, inspecting all of the wires, nothing appeared to be damaged, except a vacuum line leading into the cab, and from what I read controls the blend door actuator, which would explain why my vent is stuck on defrost, so nice score there. I found a donor car about 90 miles west of me, I made the trip this morning and scored a newer model c5 0411 pcm. Since the PCM is now what we think may be the issue, it only makes sense to go ahead and re pin and install the newer model for possible future mods down the road and even more so, hopefully, fix the issue I’m having. Back to FD again tomorrow so it will be a few days before another update. Thanks guys for the continued recommendations.

Bill Curlee

I seriously doubt its a PCM issue. Like I stated, its either a BCM water/corrosion issue or a serial data bus issue. I think the PCM will need to be reprogrammed with your VIN and operating system and then resynced with the BCM

The hand shake between the BCM & PCM is fairly straight forward but it takes a while to accomplish it. Need a good battery that wont die.

Calebxmaxx

My buddy has the computer/program needed to reprogram the PCM, so we’re good there. He’s pretty convinced the BCM is ok as it looks fine and literally nothing else is having an issue except the gauge cluster. All windows, locks, seats, air controls, radio, lights, etc. work fine. It has a new battery in it putting out correct voltage, ignition switch is new, grounds all cleaned. If the PCM does not work then I will replace the BCM. I got the PCM cheap and it was something I eventually wanted to do anyway, so I’m ok giving it a try at this point since nothing else has worked.

Calebxmaxx

Got home this morning and pulled the battery to take it to the parts store to have it charged and tested to make 100 % sure it’s good before digging into the PCM. While I’m waiting on it I checked the ground on the bottom of engine above starter and it was tight with no corrosion, also checked the ground pack under the battery and it was clean. I decided to go ahead pull the windshield wiper motor while I wait, since it only works on high, and I found where a little critter had made a home before. Upon pulling the wiper motor is when I noticed this little fella had chewed on the wiper motor wires exposing a few. Now I’m not sure that this could be causing my electrical problems, but I got them all clean, wrapped up, put back together and am now waiting on battery to proceed.

Calebxmaxx

Alright guys, I think the issue has finally been resolved. I’ve been driving the car around for a few days now and everything seems to be working correctly. After countless hours of trial, error, tracing wires and with the help of Mr. Bill talking with my buddy doing a lot of the work, we isolated the issue to be the PCM. It seems there was some sort of ground issue inside. Instead of putting the stock PCM back in, we went ahead and repinned to fit the 0411 PCM. Afterwards everything seemed to work as it should, other than the fuel gauge, but thinking that is the corrosion on the sending unit, I have been running Techron through it and it seems to be clearing up slowly. Thanks again for everyone’s help and to Mr. Bill for taking the time out of his day to talk with my buddy and helping to resolve the issue!

FRCinwhite

I just wanted to thank you guys for saving my a$$ again! I was installing my backup cam, had some issues with reverse wire not returning screen to existing source after showing cam while in reverse. Turned out I needed a resistor because I have LED bulbs. I found that fix on CF also.👍 In my troubles I pulled the BCM down to test the reverse wire shown on Directechs that I use for remote starters. Anyway that wire didn't work out, it was supposed to be a negative trigger, it stays 12v even when in reverse when it should go negative. I'm thinking that wire is used for automatic cars maybe. At this point I go the resistor route. Put the car back together, go to start it and the poo hits the fan! Gauges all go nuts, like 4 or 5 messages on the dash, the Windows won't go up and it won't start! I find this thread and read about the STAR connectors and think I was just in there, let me start there. I pulled the BCM back down and check the 4 wire connector, looks good, no corrosion. Looked at the other one and the "comb" is missing! I look in the holes where the BCM clips in and there it is sitting in the bottom hole. Plugged it in and the world is whole again! Thx again, Ken

Brewmeistergi

Thanks to the OP for posting his problem source finding. Too many folks visit and ask questions but then forget about the forum when the issue has been resolved. Best of luck with the car in the future and enjoy the heck out of it.