On board diagnostics on my 93' base coupe display DTC 41 ECM serial data circuit. DTC 54 FEDS fuel enable circuit and DTC 72 serial data link malfunction. I have torn it apart and gone through the FSM. No definites for one thing or the other. The manual is not even correct on some of the pinouts especially ckt 800 data link. I am considering replacing the CCM. Any ideas would be greatly appreciated. Thanks.

 

is there an actual malfunction to go along with these codes? or are the codes just appearing ?

Fuel enable...? VATS/PassKey related? bypassed? reprogrammed out of the tune?

data link malfunction... often harness connections somewhere. If you have the FSM drawings, you CAN trace the harness and do continuity from pin to plug, to rule out something like a bad connection or rotted harness wire. These wire harnesses are known to have some cheesy insulation that barely makes it to the federal minimum set for the automotive industry. Its dry rotted by 10 yrs, cracked insulation in places you cannot possibly see and cross signals are common in bundles inside the loom. The EFI circuits are good for this since they are exposed to weather and temp extremes under the hood.

If there is an actual engine performance issue that you know to be real, go back and work the symptoms and ignore the DTC's for now. Often you will fix the problem and the DTC goes away when you do..

 

the only real performance issue is FEDS flashing security and sys 3 times every 15 sec. when it is occuring it won't make the car die when running but it will keep it from starting periodically. progressively gotten worse. I also get a service ASR light with this.

 

That's an undiagnosed VATS issue. No real problem with the CCM, but there IS some security problem.

I'm not familiar with that year and how it works, but you are right in that it will not or cannot shut the engine down once running since its only active during cranking, but it CAN prevent the engine from starting. If that's by not allowing starter to operate, or fuel enable,. is something that needs to be determined so you can "back" into the system and get to the reason WHY. It might just be an unhappy decoder module, or simple broken wires in the key circuit.


But the "problem" is what you address, not the DTC. These codes are just there to act as indicators of which system is being effected by the problem that you are encountering. The DTCs are NOT the problem, more of an idiot light for the new millennium.

Go to the "problem" not the DTC.

Get into the VATS diagnostics in your FSM and you'll easily figure this out.

if it comes to having to do a full VATS bypass, to get fuel enable permissions again I will go AGAIN ( just did this last week and posted it) and find the link for a $14 signal generator, module bypass that you can install to drive again worry free, until it can be repaired RIGHT. Worst case, its a tired VATS decoder module. More than likely something far less sinister like a wire or something along those lines. Follow the FSM VATS flow chart....you'll get there.

 

I had some problems yesterday as I shut car down and when fob was out of range the car honked the horn and kept honking. I finally left key in ignition. When I went to leave the car would not start. I than disconnected battery to erase any ecm codes, car started. A couple of days previous I cleared codes in ccm that had some error codes in the 1.2, 4.0, and 9.0 modules. When I made it home yesterday I reprogramed my fob and a new fob, so far no asr and abs service display and no passive security which is fine with me. Just use the key to lock/unlock doors

 

I ended up putting the dash back together enough to drive the car and got service asr light and flashing security and sys again. I then realized that I had not cleared the CCM codes from before I tore the car apart. So I turned the car off and cleared all CCM codes I fired it back up and drove quite a bit. When I got home I checked the CCM again. No codes. Not sure if its fixed but we will see before I put it back together.

 

41 and 54 are generally accepted to be ECM issues and the 72 is often present after a radio head change to an after-market unit. Do you have the factory radio? If not is the radio a recent install?

You're in drive mode presently and that might be considered a 'victory' of sorts I guess.

CCM issues aren't considered to be frequent but these cars are certainly aging so electronics have to be considered I'd think possibilities.

 

I did install a Kenwood deck from Crutchfield with the adapter harness for the car.

 

If the 72 returns here's a take on the required resistors and diode to remove it once and for all. There's several procedures I believe in the FSM that mention the required changes for an after-market radio head in the C4. Midway in this article right after the image of the DIC control panel it's explained.

http://tech.corvettecentral.com/2011...trouble-codes/

Here's a copy of the TSB:

http://www.corvetteforum.net/c4/dave8476/index4.shtml

It's my understanding you can go months without codes after an install and then out of the blue here come the codes. I still have the Bose so I can't offer any "first hand" knowledge of the problem.

 

Thanks for the help.

 

WVRZ-1 thanks for your help. I put this whole thing back together still getting 41 and 54 also now 43. this is after having an intermittent problem with the KS circuit. I put 2 new knock sensors on and had no problems. Sorry kinda going backwards explaining. So after putting all back together I get 41,54 and now 43 could this be a bad ECM. I would gladly pay for a new one for this to be fixed. I am logging with datamaster and trying to finish a tune but this won't let me.

 

Does it have a 'modified' PROM in it presently? Do you have a stock PROM?

 

I was in the middle of tuning it last year and I had to stop because I could not get rid of DTC 43. So it is modified but would like to have it as close to stock as possible when finished.