Good afternoon,

I have a 2009 C6/1LT/auto that has served me well for many years. I am the second owner and have driven the car daily since 2014 in which it had 68k miles. The car has around 170k miles now and has developed some strange electrical issues. The car has been to several shops and dealers who have thrown a boatload of parts at the vehicle, only to have the problems return. As of yesterday, the car has experienced:

• Entire radio display is dark and will not even provide backlighting to the buttons when the headlights are on.
• Navigation head unit is non-functional and even the CD stuck in the stereo refuses to be ejected.
• One headlight (usually the driver side) goes out when the Left turn signal is activated.
• Map lights and other lights stay on even after leaving the car, but lock/unlocking cures this (sometimes).

I recently took the car on a 800 mile road trip and found the interior lights staying on at rest areas, even after leaving the car and locking with the keyfob. This would stay on after the 20 minute "Retained Accessory Power" feature and remain on until I started the car. Within the past week, the car has experienced:

• Alarm going off even after you've unlocked the car with the factory keyfob/remote.
• Unable to pair a second keyfob/remote using the procedure in the owner's manual.
• Random lights such as tail lights, reverse lamps, and other lights on when parked.
• Interior bulbs burning out at random (driver side footrest, DIC buttons, HVAC defrost).

Dealers have been unsuccessful in repairing the car after throwing numerous parts at it. The car has received two alternator replacements (based on this I am assuming #3 is what's in the car), a new fuel pump and fuel pump sending unit (they were diagnosed as bad), multiple Optima Yellowtop batteries (three replacements), and it still drains the battery after sitting for several days. I have to keep the car on a battery tender daily even though it sees 250-450 miles of travel per week, as it's a daily driver.

The car does have an aftermarket stereo in it, installed with a PAC RP5-GM11 interface adapter, but that has been installed since 2014. Just to rule that out, I swapped in a different aftermarket stereo just to eliminate the existing Alpine head unit (in case it had an internal short). I can try putting the OE stereo back in, which would enable the factory XM and OnStar features, but am not sure if the radio is the culprit - if it is, why did it take 8 years to occur (and there are no shorts on the harness, connections were soldered and not crimped).

Today the car showed all of the same electrical issues with the driver side headlight turning off regularly when the turn signals were enabled. Multiple times I would hear relay noises that shouldn't be happening, even after I opened the hood. The fuel pump relay (#55) is very hot to the touch, and the battery isn't charging after a 20 minute drive - when put on a battery tender it showed the battery was depleted. Voltage when sitting is around 12.1-12.3V right after shutting off the engine.

I'm afraid to take this thing back into a shop again and receive thousands of dollars of parts thrown at it and no resolution. The only thing I can think of is try cleaning connectors/grounds, put the factory stereo back in, and then hope I find a decent repair facility that isn't going to play the "keep replacing things until it fixes the problem" game because that's all most shops have done so far.

If you had an excellent condition C6, with only this minor problem, what would you do?

 

I'd bet the problem is in the fuse box. If I remember correctly the fuse box is 2 halves, top half has the fuses and relays and the bottom half has the connectors for the associated wires. Perhaps there is a bad connection? Also if you can see it, look at where the positive cable connects to the starter, that gets cooked and breaks and can cause all kinds of electrical problems

 

Thank you, just looked in the fuse box and did some troubleshooting. I removed relay # 47, the one marked "LOW BEAM", and still have both low beam headlights upon unlocking the doors. Can someone confirm that the low beam relay only affects manual operation from the turn signal stalk (or daylight sensor) and that there's an alternate path for the headlights to be powered when unlocked from the FOB?

Positive cable looks nice and clean at the battery and starter, that's one of the first things the dealership did - clean all the battery connectors and terminals.

Is there a chance the BCM under the passenger seat footwell could cause these issues? I have spilled small amounts of tap water but don't recall any of it getting beneath the carpet (we are talking several ounces here) and most of it was on the driver's side. If it is truly from water damage, would it cause such intermittent behavior in systems not related to the BCM?

This is getting interesting but since no shop can seem to figure out the issue, I'm kind of enjoying the challenge trying to figure it out myself now. After all, the only difference is they will charge to make educated guesses (and bill you if it's not the right fix).

 

Are you sure it's not the hi beams on with unlock? If relay #47 is removed, the lo beams can't come on.

 

Start with a known good battery & all electrical grounds clean & tight...all kinds of electrical gremlins pop up when either of the two need attention

 

Winjr, good catch. It indeed was the hi beams on with unlock. I removed the other relay #39 to test that theory and low and behold, the hi beams do not come on upon unlocking the car.

449er, yes there is a known good battery in the car and currently working on cleaning up the ground terminals. I'm looking into an AllData subscription or one of the service manual books, just to be sure I've got all the grounds, and potentially even putting the original (non-Nav) radio back in to eliminate the potential for an extra floating (or bad) ground connection point.

Looking at the photo posted, I only have one headlight on at times, yet it appears the headlight signal coming from the BCM is for both headlights, would this eliminate everything from the BCM downstream? I've pulled the relay, cleaned all contacts, and let it sit all night. I've also pulled the turn signal and brake light relays & soaked the ends with contact cleaner to ensure those aren't intermittently making a connection or confusing the BCM (if that's even possible).

Thanks everyone for the suggestions, I'm looking forward to getting this car back on the road as it has been an enjoyable car to drive.

 

I too suspect wiring/ground problems. You need a diagnostician and not a parts installer.

You might PM member PAPAWANA who can email you a C6 wiring diagram.

https://www.corvetteforum.com/forums...ams-offer.html

 

Thank you C6ToGo, we are greatful to have members like PAPAWANA to help with things like these.

As I have already brought it to multiple Chevrolet dealers who all charged for diagnostic and only replaced the problems they could see (I bet if I brought it in right now they would change the headlight assemblies), yes I agree this needs a diagnostician and not just a typical mechanic that services "all makes and models" who did a great job installing the alternator, but did not completely solve the issue.

Going to spend more time troubleshooting it tonight to see where I get. Knowing the location of all the grounds and verifying the connection with a voltmeter to multiple chassis points should hopefully point me in the right direction.

Any other tips/tricks/advice is sincerely appreciated!

 

Your stereo issues could also be caused by a bad interface (RP5-GM11). These have been known to go bad. Installing the stock stereo should tell you whether or not the interface is bad. I don't think a bad interface would cause your other issues though, but you never know.

 

Appreciate the heads up madsonp, that is a good point. Last night I removed all the relays I could find and soaked them in electrical contact cleaner. Removed two of the grounds I could easily access (near the battery area) and cleaned them until they were shiny with a wire brush. Hooked up the same battery (which appears to be good, it held a charge overnight without the car connected and only a battery tender hooked up to it earlier). The car started up solidly, no error codes or warnings, this time the radio came on and I was able to see all the lights that were usually dark on the HVAC and DIC buttons. So they were not burnt out after all.

How would you proceed troubleshoooting from here on? Right now I have an extremely dark dash backlight (it only shows the text in the DIC if the brightness is turned all the way up, one click from maximum and the text is barely readable). The voltage on the dash is 14.3 when running and around 11.7-12.1 after its been sitting for a while. The alarm did go off when I exited the car after a 20 mile drive, but didn't go off again when I went to open the door after doing a lock/unlock cycle. Both headlights are now on, I may still clean the ground near the driver side headlight, but am not sure what else to check short of removing the RP5-GM11 interface.

I really hope it's not the PAC interface, as it's a PITA to get to based on how I originally mounted it, but that was to keep it from rattling and also make room for the (rather-deep) head unit I originally had. But the car now drives good, and doesn't seem like it's starving for fuel, so at least I'm able to drive it around some.

Really thankful for all the help, wiring diagrams, and pictures I was able to get from this forum!

 

this last part right here. My starter to cable nut was loose and was causing problems no one will ever figure out. I found out what it was cause I change headers on the car regularly every 2 years and that's the only thing I prob did wrong. Buella

Careful though, last year I did it again and tightened too hard and broke my starter selenoid. Had to get a new starter 😭

 

Well it sounds like you made progress cleaning the grounds and relays, I suggest cleaning more grounds, there's two ground points by each fender towards the from of the car, I suggest cleaning those also.

 

Thanks, I did not get to those, and they seem to be in an area where corrosion builds up just from the road dirt getting kicked up into the engine bay and sitting there (I do clean the areas out regularly though). Anybody have a quick way to remove the front bumper cover to get to the headlight assemblies? I did have the front bumper repainted recently due to rock chips, so perhaps the body shop forgot to attach the ground wire tightly when putting everything back together. I'm also wondering if the shop that did the fuel pump didn't bolt everything back securely when they dropped the tank (they did, for some odd reason, drill sharp screws where it nearly pierced through the driver side seat and I had to make them cut it off with an angle grinder).

Never got an explanation as to why an authorized Chevy dealer needed to install the fuel tank in an alternate way, but they did offer to repair the carpet and interior for free).

 

this and
Look to pick up a service manual and schematic. No use doing anything without one and a decent multi meter.

 

You're on to something here. 11.7 - 12.1v is way too low. Whatever is causing this is most likely the root cause of your electrical issues. Looks at the usual causes of parasitic draw, and check for ~14v at the battery while the car is up to temperature and running for a while.

I'll hazard a WAG (wild *** guess) it has something to do with the aftermarket radio.

 

I believe those two ground points are for the headlights also, I've replaced my headlights, and there's no ground points at the lights, just connectors as you can see in this video.

 

The (only) headlight grounds are G101 and G102. They are shown in the schematic below and in the pictures from madsonp's post #12. Good idea to check them out and clean as necessary. You will notice that each ground is connected to only one headlight, however G101 & G102 are also used by other circuits.

 

Every time I have had really bizarre 12v electrical issues (which is not a lot) it has been a ground issue. We had this happen earlier this year commissioning my boat for the summer. Just crazy nonsensical things happening, I was furious because I kept changing and disconnecting things but the results made no sense at all. We eventually realized there was a ground cable that was hiding, and we missed when hooking up the batteries for the season. Reattached and everything was instantly back to normal. I would definitely chase and clean any and all grounds.

Another thing I might look at is the wiring for the stereo. You changed the head unit but was any aftermarket wiring left behind when you did? Something could be wrong or just chafed.

I would check any and every instance of non stock wiring on the car. If there's anything the previous owner installed, that would be high on my suspect list. People do a terrible job with 12v wiring.

These cars are definitely a bit twitchy about electronics so it wouldn't surprise me if something very simple was causing all of these symptoms.

For the record, I ignored everyone who was saying Optima was sold semi recently and their quality declined. As it turns out, everyone else was right. The quality is horrible now. My car would discharge a battery in a week or two at the max and recharging was killing them faster than it should have. After I changed to an AC Delco battery it can sit for a month plus and not be dead. I don't think that's your problem, but I would definitely change brands if you kill another battery.

 

Endus, that makes a lot of sense and when I checked the ground connectors for the headlights mentioned earlier, they were both extremely corroded. Guess that's what happens after 170k miles or nearly 14 years of driving. As far as the aftermarket wiring - yes, I plan to check that also, hopefully soon, as I want to eliminate anything that can cause the strange issues. I also did see a few other grounds that had corrosion so plan to clean those up this weekend. The car is driving as of now, and except for a few odd issues (such as the alarm going off at random times), it is throwing zero error codes and doesn't feel like it's starving for fuel at all, so I think we are all on the right track here. Will clean the rest of the grounds and any other electrical connectors and report back once that is done. Thanks everyone!

 

On passenger side under carpet's main computers
There're 3 large *blue* multipin connectors w/ locking levers.
Been reported due to flimsy panel passenger weight was xfered contacting one or more of these connectors.
Connector(s) loosened over time resulting in mysterious, untraceable intermittent electronic behavior(s).

Release locking clamp for each connector, pull apart & apply dielectric grease to male pins.
CAREFULLY resecure so-as to not inadvertently bending any of those pins as they enter female side.
Considering age & miles this could be source of issues & well worth checking -- if only to rule-out.

Owners experiencing this isolated problem solely by accident.
After resecuring they'd place a shim to prevent panel coming into contact w/ connecters going forward.
One guy used Pink Pearl erasers for shims, use whatever works.

Check connectors out.
Make certain all 3 are still firmly connected -- even if you don't separate.
Easy quick check which if lucky solves a real PITA issue.
G/L