So I just got my 94 Coupe last week. It's the winter in Connecticut, so I'm tearing into the interior to clean it up for spring and part of that is re-doing the lousy stereo head unit installation by the PO. (Can you say speaker level outputs into amp inputs? It's loud at vol 3. Just makes me wonder what's wrong with some people) Anyways. I pulled the crap HU out and put it aside on the bench a day or two ago.

Today I decided that I've had the doors open and interior lights on enough that I just wanted to start the car and let it run for a little while to make sure everything was fine and I wouldn't end up having to jump it. Went to start it, and nothing. Dash lights up, but no crank. I thought to myself "is the clutch in, trans in neutral, foot on brake?" I mean I know how to start a car is there something I'm missing here. Checked the voltage on the battery: 11.99v -clearly not the problem. Couldn't get it to start. So on a whim I just plug the aftermarket HU back in and boom she starts right up.

So... there is no OEM harness in my dash, it appears that the stock harness was cut out and the aftermarket one spliced in with butt connectors. Why would the car not start if the stereo wasn't plugged in? Is there something that needs to receive remote input from the stereo in order for the car to start? (In my case obviously there is, but I guess the question is SHOULD there be? and what could it be?)

Thanks for any help guys!
Dave

 

OMG... they have messed you up big time...

It sounds like either the CCM is being messed with or they somehow integrated the starting circuit with the car stereo.

You need to get the Factory Service Manual. It's available on eBay on CDROM for about $15.00. This is the paper manual in PDF format.

GET THIS... and then start tracing wires... that's the only fix for this problem.

 

Thanks for the reply.

I am planning on getting the FSM, but didn't realize I could get it in digital form so cheaply. I'll be grabbing that immediately. I'm am very experienced with stereo installation and oem stereo integration, but it certainly seems like something is going on here. But hey... at least I figured it out and was able to get it started! It just puts a little bit of a delay on me getting this shoddy work out of my car.

 

between your knowledge and the FSM, you will be ok.

I am sure you will find the problem in a matter of minutes, once you see what wire(s) were crossed!!

 

Ok, so I've determined that this harness has been installed,

http://www.metraonline.com/part/70-1856

and plugs into the plugs for the radio unit that is in the passenger side storage compartment in back with the jack. The radio unit does not exist.
So how does the aftermarket HU keep the car from starting if it's not plugged in? Doesn't make sense to me.

 

Just an possibility that they tapped into your air bag circuit. Unplug the radio and turn the key to on and see if you have the service engine/ heck engine light in your info display above the radio and heater controls.

If there is no service/check engine light you have no power going to your ECM.

One other question, will the engine turn over (crank)?

 

I have determined that no wires were cut in the harness. The stock wires with the connectors attached were just tucked way back in the dash. The Metra harness runs from the connector at the radio unit in the storage compartment up to dash where it is attached to the aftermarket radio harness. Nothing is cut or tapped in the storage compartment either. The stock radio unit is gone, there is nothing in there, so maybe there is a wire in that harness that requires output from the radio? I don't know.

I highly doubt that the airbag circuit was tapped during a stereo installation. But I guess anything is possible when you don't know who did the install. I didn't notice any lights in the info display above the radio when I turned the key. I'll check all of that tonight, and maybe take a video of what's happening.

The engine does not turn over. When the radio is unplugged I turn the key, and a couple of dash lights (I know I should have taken note of which ones exactly, but it was like the brake light and something else) flash and nothing happens. I do hear what I think is the fuel pump running. As soon as I plug the radio back in, turning the key starts the car up perfectly.

 

Not sure how much of your dash you have taken apart, but the thought of VATS crossed my mind while reading. If memory serves, there is a wire leading up to the ignition switch that reads the "chip" in the key. The security light in the dash will tell you if you're having problems with it. Thinking of the radio wiring, there "shouldn't" be anything that keeps the car from cranking. But, down where the radio receiving unit is, there are a lot of connectors that may need looked at. If you do go poking around down there, be sure to label plug to plug connections. they look very similar, especially if you're hanging upside down under the dash.

 

VATS came to mind immediately for me too. But I don't think that's the root of my problem. It's as simple as:
radio plugged in, car cranks and starts
radio not plugged in, car does not crank

I have a little time each night to play with the car, and next weekend is a long weekend. I'll get it figured out.

Thanks for all the help so far!

 

Out of curiosity, have you started it up, then plugged the radio in? I'd be curious if it died. But, I'd probably trace out the wiring before I did that on the radio harness. Back in the summer I was having issues with my radio and ended up disconnecting everything, then reconnecting one wire at a time. Ended up being a bad head unit, but with the radio receiver over under the glove box, it was an "interesting" trouble shooting. Perhaps try the radio with out the amp. I feel like I'm just spit balling...

 

Thanks for the help so far!

The car doesn't start without the aftermarket HU plugged in. I could try starting the car and then UN-plugging the HU to see if it dies. Maybe that's what you were thinking?

There's no wiring to trace. I've already determined that the only thing that has been done is the aftermarket radio has been installed using the metra wiring harness in place of the stock head unit and radio unit in the rear compartment.

I'm going to monkey with it tonight again I think.

 

Ok... a little background here...

In 1990, they added this little box called the "CCM" the CCM - Chassis (or Central) Control Module acts as a traffic cop to manage data between the PCM/ECM and the ABS/ASR computers, and other computers and systems within the car.

This includes the audio and climate controls. This is also why a SYS warning (CCM error present and is represented by a SYS message flashing on the Speedometer display) will occur on some later C4s when the stereo has been replaced.

The next facet is the topography of the audio system. The head in the dash is a dummy... it simply holds the tape and CD player, and presents display data for the radio and CD.

The other module is the RDM (I think). That module is the tuner/amp for the audio. It is the brains. It resides either in the dash behind the glove box or in the ABS storage bin behind the drivers seat. The box sends either amped signal, or line level signal, to the speakers. If it is Delco only, then it's amped, if it's Bose, it's a line level signal, and it will trip relays to power the amps.

You see, the CCM is VATS... that is what does the handshake with the key to initiate start. Without, you have problems.

What bothers me is that VATS won't stop cranking... I had my ECM lose communications (the UARTS both died) and it could not get VATS approval, all it did was crank.

Again, this requires some analysis... I think you are on the right track, but understanding the topography should help.

For what it is worth, not having the RDM module in place should have zero effect on things.

 

Bogus, Thanks for the detailed response!

I need to check the CCM codes (I think I saw an article on how to do that) to see if there are any outstanding.

I think the only things that are missing from my car are the head and the RDM. The harness does not appear to be hacked at all. From everything I have read there should be no problem with those items being unplugged and removed. Also, it was my understanding that 1993 was the last year that there were any errors that would be sent to the CCM if they were unplugged per the TSB that addresses that.

Regardless, if I just swap out this crap HU with one of my better Alpines, I would think that the car should start and this all doesn't matter so long as the car starts.

And as you said, if VATS still allows cranking...there is something else going on here.

Anyways...is it spring yet? Can I just go drive my car? LOL. I just bought this car and I've wanted a c4 vette since I was 10. I just want to go for a drive!

 

The radio is not relative to VATS. And the radio is not typically going to cause the car not to run. I have completely removed the radio and so have other racers and the car will still run.

I can tell you that the air bag system is.

 

l98tpi: I think you nailed it. I think the last time it started when I plugged the radio back in was just a coincidence.

Last night I was futzing around with the car, without the intention of starting it because my daughter was asleep, the HU was unplugged, I turned the key, and it turned over. I stopped because I didn't actually want to start the car. Too loud to be running when she's trying to sleep.

Today I went out and tried to start it with the radio still unplugged, no crank.
Plugged the radio in, still no crank.

Looked at the various lights on the dash. Put the key in and turn to run: everything lights up, it settles on the Battery and Service Engine light on. Turn the key and the Airbag (above the radio), Brake and Park lights(next to the aux gauges in the cluster) light up. Let go of the key and the brake and park lights go out and the airbag light flashes a few times and then goes out. Battery and Service Engine stay on throughout. Checked the battery and it has 11.7v which should be fine to start the car, I'd at least expect a slow turn over or click if the battery was the problem.

Tried the horn...no sound. So clockspring? The car does have a bit of a wobble in the steering column as is common from using the wheel to get in and out of the car.

Looks like I may be doing a repair to the column sooner rather than later. I had hoped I could make it until next winter for such a major dis-assembly.

On another note. I'm not finding the FSM on CD on ebay easily. Maybe I'm looking for the wrong thing? All of the ones that keep coming up are only book 2 from what I can tell.

There's also a set of physical books on there for under 90 shipped that I may just buy.

Thanks for all your help so far guys!

 

Just went out after I wrote that post, so maybe 5 mins later...Started right up.

 

Welp, I think I just had my first bout with VATS. I took a close look at my key and it appears to be very new. So new that the molded plastic that holds the chip was protruding past the contacts a little bit. I shaved it back, and I'm getting consistent starting. Also I noticed before when it wasn't starting, the security light was flashing. It's not flashing anymore.

I also pulled the codes using this article:
http://tech.corvettecentral.com/2011...trouble-codes/

and I got the following codes all preceded by an H meaning they are not current
32 LCD data circuit open or shorted to ground
34 Data clock circuit open or shorted to ground
36 Data strobe circuit open or shorted to ground
38 M clock circuit open or shorted to ground
53 Pass-key – key detection circuit open or shorted to battery

Seems that 53 would be the code that would be thrown if the chip was not making contact. Anyone care to chime in?

Thanks again guys!