When I took my C5 to get SMOG'ed, it turned out the "Check Engine" light was burned out. Since it is also the official MIL (Malfunction Indicator Lamp) for the emissions system, you cannot pass your SMOG test if it isn't operational. Very long story told short, I decided to do a number of repairs once I discovered how to read the trouble codes using the DIC. This thread is about my repairs and upgrade of the instrument cluster itself.

Since one bulb has failed, and they're likely all the same age, i.e., original to the car, I decided to replace every bulb I could get access to with a new part. I looked at LEDs, but you have the issue of polarity, and maybe having to pull the cluster again if you have one in the wrong way. Reasoning that the 2003 bulbs have lasted this long, and knowing the new ones are likely to outlast me, I just went with simple replacements, which are very cheap.

However, one of my frustrations with the C5 instrumentation is that the whole panel is like a black hole during daylight conditions. Somewhere along the way researching which bulbs to buy, I found there are two bezel upgrade kits: one aluminum; and one ABS plastic. There were complaints from some that the glue-in aluminum bezels were messy and difficult. The ABS versions went in with double-stick tape, and supposedly are simpler. I went with the ABS versions.

Here's the stock unit without the added bezels.


Standard Z06 instrument cluster with clear plastic shield removed.

Here's the ABS bezel kit components.

Bezel Upgrade kit.

There were no instructions for the install. I trial placed them and found they don't "snap into" place, but it did reveal where I thought the double sided tape should go. It takes a little effort to work the tape around the bezels. Don't take off the green tape protecting the top side. Instead, use the green tape on the top side to let you work the sticky side around the inside of the bezel with minimal contact of the sticky side. It's easier to do with the tach and speedo bezels because of their larger radius turns. The only caution is making sure no black from the tape shows along the inside edge of the bezel as that causes it to look blemished, or out of round.

Also, the 4 open-ended bezels don't fit perfectly. They have to be gently and carefully worked into place. They are probably perfectly dimensioned in the mold, but like metal, appear to spring back a little bit after they're released from it. I read somewhere in these forums that you shouldn't lay the instrument cluster on its back for any length of time as it can create a problem with the liquid damping of the instruments. I decided to heed that warning, and kept it vertical while doing this install. That does make the install more challenging, but it's doable.

Here's the installed result with the clear plastic shield still off:

Plastic shield off.

Even after it was cleaned and re-installed, I feel like the instruments are so much easier to pick out and focus on. I'm quite happy with the enhancement.

Clear plastic shield re-installed.

Since the outer, black ring of the instrument cluster had to be removed anyway, I decided to start replacing the bulbs revealed there first. Those would be for the DIC controls on the right side, and the HUD display (optional, not on all cars) on the left. However, when I took the bulbs out, they're on a setup similar to the T5 sockets/bulbs inside the instrument cluster itself, but not the same as the T5's. I found out they're of a kind not mentioned when I was doing my research. And, they're blue too. I'll have to find out what they are and order some.

Back side of DIC controls with 2 of 3 sockets/bulbs removed.

I understand the black lights used for backlighting the whole instrument cluster are not available, and not replaceable anyway. I had trouble finding a picture or part number for them. However, I never ran that fully to ground, so I'm not positive that's true. I decided to take this close up to provide a reference for other explorers in the future who may want to go further into the issue. If you look at the first bezel install photo above, you'll see both black light tubes, one on either end of the instrument panel.

Close up of black light fluorescent tube on RHS of panel. It's a clever idea.

C5 Corvette black light for illuminating the instrument cluster with lights on.

Cheers,

 

When my C5 was SMOG checked a few weeks ago, the technician told me my Check Engine Light was inoperative, which meant it could not pass its SMOG test. It is also the MIL (Malfunction Indicator Lamp) for the emissions system, and it must be operational to pass. With the OBDII plug of my C5 connected to his machine, he ran a particular test that was supposed to make the Check Engine Light illuminate. It did not light up during the test. We both took that as proof positive the light was burned out. The official PCM code thrown on the DIC is "P0650 Malfunction Indicator Lamp Control Circuit" as the fault.

Long story short, I replaced the Check Engine Light socket and bulb with a part I bench tested using a 9V dry cell, so I know the new part is good. I looked at the old light/socket assembly under a magnifier, and it looked good. I tested it with the same 9V test setup and it did indeed illuminate. So, it wasn't bad in the first place.

Instrument panel disassembled to access light bulbs.

Looking for another reason why the light did not go on, I speculated that maybe it was because one of the other bulbs on the common ground trace was bad. Perhaps it was some some sort of "serial circuit" like thing going on? So, I changed those two bulbs too, replacing them with known, good, new bulb/socket combinations. I tested each of the old bulbs with the 9V setup after removal. They too, were both good.

Three sockets/bulbs replaced (blue check) on common ground trace

I was perplexed. I'm definitely not an electronics tech. It's probably my weakest automotive skill area. However, I do know that sometimes you get lucky, and some failing part of a circuit board visibly gives out a clue it has failed, like showing black burn marks or other obvious discoloration. I didn't see anything obvious on my circuit board. The only part on the circuit board that looked discolored is the one shown in the photo below. I don't even know what it's called. It actually looks more like oxidation of the metal rather than a burned out part.

Discolored component. Failed? Probably not. It may just be oxidized.

That really was the extent of the analysis I could perform. I strongly suspect the problem lies elsewhere. But, where does that "elsewhere" live? The only other thing I could hope for, based on what I did, was that there was some kind of "seating" issue with the bulbs, and that maybe my replacing them would solve the problem? I think the probability of that is low, but it's all I've got at the moment.

So, I buttoned the whole thing up again, and will test the instrument cluster in the car tomorrow to see if the Check Engine light illuminates at startup. I'm going to search tonight for other information on what could be wrong based on the P0650 code, and try to find the circuit diagram for the various components that can turn the MIL light on. Any suggestions about the code or the C5 MIL circuit by more experienced users here would be welcome.

Thanks in advance,

 

Years ago I had one of those flexible circuit boards on the back of a instrument cluster crack on me (not a corvette). I would check the connection with a meter, trace the connection back as far as you can. Seems like it could be a bad connection somewhere maybe.
With key on engine off the MIL should light for a couple seconds, shouldn't need any test equipment for that.
That discolored component looks like a heat sink, I wouldn't worry about it.

 

Thanks for the response, and the information. I do need things to try, so that's helpful.

Cheers,

 

From the picture of the sockets, it looks like the contacts of the bulb socket are going under the flexible circuit board. If they are truly under the circuit board, then that would be your issue.

Gary

 

I can see why it might look like that, Gary. However, they are on top of the copper. They make a little trail that's visible when you untwist them and pull them out.

Cheers,

 

I did find one promising tidbit from a posting by lucky131969 back in 05-11-2010. However, it's for a 1998 C5. The underhood fuse box for my 2003 has a slightly different layout.

MIL circuit for early C5.

Now the trick for me is to turn information like this into a fuse # that I can pull and check. I'm guessing it must go through a fuse there. Also, I'll try to find the 2003 circuit layout.

 

From my '03 service manual.
doesn't look like it goes though it's own fuse. gets grounded at pcm to turn the light on. Instrument cluster is fused #19 but that's for everything.

 

@Old School

Thanks so much for posting the diagram. It's very helpful.

It would have been so nice to have a fuse in the diagram of the circuit, assuming it was the problem. That's any easy fix. I did find two references to fuses for the PCM itself in the underhood electrical center. They are fuses #16 and #23. It would seem unusual for something like a PCM to have two power sources, but maybe it's a planned redundancy? I'll take a look at both, just in case. The car was running, so the PCM must have been working.

I believe the PCM is under the battery, and behind the inner fender shield. I'll verify that, and see if I can get in to take a look. I've read leaks can cause corrosion in the area. First, I'll look at the electrical center and see if I can spy the brown & white wire they mention in the diagram. Perhaps there is some issue there?

Thanks again,

 

I did pull, inspect and reseat several fuses inside the cabin, and in the engine compartment. Notably, the 2 to the PCM, 1 to the unintentional load monitor, 2 to the HVAC system (I did some work on it too) and the 1 to the instrument cluster control. Not seeing any problems, I reinstalled the instrument cluster, and low and behold, the Check Engine light is now operational again.

The thing is I can't say exactly what solved the problem. I replaced and reseated 7 instrument cluster bulbs, including the Check Engine bulb. None of the old ones were obviously burned out. They each lit up using a 9V dry cell battery. Was it just the reseating of the new bulbs what did it? I just can't say.

In researching the issue, I had stumbled upon a comment in a years old thread here saying one fellow had his Check Engine light come back to life after the battery was disconnected overnight. I had the battery disconnected for several days, so I could safely pull the airbag system and replace the HVAC actuators. Was that the real cure disconnecting the battery? I just can't say. However, for anyone reading this thread in future, I'd suggest that as the first thing to try. It's a pretty cheap fix, time and money wise, if it works for you.

Cheers, and Happy New Year too