36Volt

So, '92 base Corvette LT1, Automatic.
This is another "system" flashing, service ASR, no start.

Here's what I got........
When KEY ON and service ASR light does NOT come on - IT starts, runs, shifts awesome. Although almost ALWAYS soon after key on engine running the "system" flashing, service ASR, cycle begins, far as I can tell has no effect because even the cruise control, traction control and ASR appear to work and DOES NOT DIE when running as this is NOT the issue. Runs great. Actually Really great. I went through all the opti, trans, everything, was not even running when I bought it (bad opti) but runs WAY to good to suspect a module just yet. Doesn't miss a beat.

But
When KEY ON "system" flashing, service ASR, DOES occur before crank it cranks but WILL NOT start I have :
A) Is NOT VATS because starter engages.
B) 48 PSI fuel pressure, back probe finds 12V to fuel relay out of ECM pin D-7 - YES.
C) Tachometer movement - YES
D) Spark - YES
E) Injector pulse - ground pulses from ECM Pins D10, D11 - NO

Suspect - Serial Data "intermittent open" or internal fault in CCM or ECM

The first time I scanned with my Snap on MT2500 (which also talks fine to my 95 LT1 Firebird) it communicated ECM codes 41, 72, when I scanned the ABS codes 72, when I tried to clear the ABS codes I lost the ability to re-communicate with the ECM through the MT2500, still can't. This is well, weird. no matter.... switch to....

OK, so using onboard diagnostics jumped the A/G pins on ALDL and got:

Module 1 CCM
C41, Loss of ECM serial data communications?
C72, LCD dimming output circuit open or shorted to ground?
H41, Loss of ECM serial data communications?
H72, LCD dimming output circuit open or shorted to ground?

I do not yet know the distinction between the "C" and the "H"

Module 4 ECM
2 readings depending on status of EBTCM
When EBTCM HAS codes I get:
--- No code
But when I clear the EBTCM and re-read all the codes I get
the dreaded ERR!!!!
But the EBTCM stays clear for only short time then ECM goes --- again

Module 9 EBTCM (ABS/ASR)
H72 when I clear it, comes back shortly after effecting the ECM as described above.

So I know this is common reason 92 and 93 Vettes are disabled sometimes even abandoned. I say BULLY.

I am NOT going to alter or modify, I want this to be all STOCK, and working.

BEHAVIOR -
SO MANY POSTS ON THIS-
Some say ice on ECM makes em start, change chip from VATTs, this and that, I have 18 ASE Certs resulting in 2 Masters, associates degree in advanced automotive technologies applied sciences and am certified in 32 electrical type certs for aircraft, even 3 years at a Cadillac Dealership as the head drivability technician.
I have learned the hard way about snake oils.....

So forget Ice, throwing resistors at it, ETC this is what actually happens:

When say, I drive to store, and come out and now won't start I found with the door closed and the axillary sustained power on to the radio I can cycle the key till the cows come home with no change.
If I open the door and cycle the key with the axillary sustained power disabled eventually I will get a moment the "system" flashing, service ASR, DO NOT STAY ON and BAM it starts. Then once again, runs fine till I shut it off. It has taken me up to 50 cycle trys before, when lucky only 5 or six key cycles.

OTHER INFO
There is an aftermarket stereo in this car. I read this from some intellect smarter than me about this:
LED dimming circuit

"The purple/white striped wire at the radio head connector (C1 position 2) requires a 10 Ohm resistor and diode in series with the pink wire. The same pink wire from connector C2 position 8 is used for power. Connect one side of the 10 Ohm resistor to the pink wire. The diode should be installed in series with the resistor. Diodes are an electrical check valve allowing current to flow in one direction only. Diodes have an arrow on their barrel denoting direction of current flow. The arrow should point away from the resistor towards the purple/white striped wire. One side of the diode connects to the resistor. The side with arrow pointing out goes to the purple/white striped wire. This will prevent “SYS” from flashing while you’re enjoying the new sound system."
I think this was found on THIS SITE.

THESE ARE MY QUESTION (s):
1) Would Dimmer signal to stereo really inhibit ECM fuel enable?????
2) What do the H, C prefixes on the module one codes mean from above where I stated codes found, both had same numerals.
3) Where is the dreaded serial data junction between these modules actually located on a 92 Vette on the brown circuit 800 tan wire?

Basically I have restored ALL this car less this condition based on my own general GM knowledge, I do NOT yet have the factory manuals for this but have them on the way.

There are so many gurus on this site it is possible I could fix this last issue before my manuals come if I am lucky and someone points me in the right direction.

I hope I put this post in the right section........

Cliff Harris

C means the problem is Currently happening.

H means the problem is Historic -- it happened in the past but is not occurring right now.

Refer to this list of error codes and what they mean:

http://forums.corvetteforum.com/1576116036-post35.html

36Volt

Oh yea, Duh I'm just tired I guess

you are RIGHT History and Current
Definitely what C and H are.

On the LED display the 12 is replaced by the --- as no codes.

Thank you for clarifying that, those are in the CCM Both history and current 41 and 72
Thanks Cliff AWESOME that's a start for sure.

36Volt

I'm checking the codes you linked me to compared to the list I have, think mine list is pretty close to the same but double checking, thanks again.

36Volt

So my H72 code on Module 9 EBTCM is History Serial Data Link Fault ASR wich is strange must be pretty quick "Current" status Because after clearing the EBTCM code and watching My ECM code be ERR, then back to --- (no codes) by the time I go back to the EBTCM it is already History, Hmmmm.

jispr

Your easiest solution would be to bypass "PassKey" and Vats. My '93 would not turn over till I bypassed the passkey. Then it would not start till I bypassed Vats. Think I spent 100 to 150. ECM of NC has the plug in Vats bypass and the passkey is a resister mounted inline with the key harness and can be had on ebay. Takes 10 minutes for the vats and an hour for the passkey. Course u could go the new key and cylinder and TRY to replace the ccm. And actually "ice on the ecm" lead me to have mine remanned. The ice worked

Hooked on Vettes

Here's the Technical Service Bulletin concerning a CCM DTC 72 when an aftermarket radio is installed.

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

Your no pulsing of the injectors is probably due to the serial bus problem. This prevents the CCM from communicating with the ECM.

When you turn the ignition key to On, the CCM reads the resistor value of the key
pellet. If it matches what the CCM was programmed for, it enables the Starter Enable
relay by placing a ground on the relay primary coil. This enables the Starter to crank
when you turn the key to Start.

The CCM also sends a message via the serial bus to the ECM. If the ECM responds with the proper handshake the ECM will pulse the injectors.

There are 4 devices on the serial bus. ECM, CCM, ABS and C68 AC Programmer.

To eliminate the ABS module which is located behind the drivers seat in the storage
box disconnect it.

Disconnect the negative battery terminal. Then disconnect the 55 pin connector going to the ABS/ASR Control Module.

This will remove the module from the serial bus. If you still have the no start problem
it points to the ECM.

Tom400CFI

Listen to this man. He knows this stuff, and he helped walk me through a similar issue.

http://forums.corvetteforum.com/c4-t...-advise-3.html

36Volt

MANY THANKS - I am going to do the radio resistor/diode correction first. Next will check for resistance in the tan circuit 800 serial lines.

Geardo

I'm subscribed to this thread, sounds a lot like my problem on my 93

36Volt

Yea Hi Geardo,
Just got my resistors and gonna proceed. I am going to stick with it until this issue is resolved without butchering up the system. Original stereo is long gone so have to get the "system" to quit blinking, the rest is going to be getting my serial data to quite timing out, I will post progress and findings along the way with the expert help of you and others on this site maybe we can get another successfully repaired fussy 92/93 Vette fuel enable condition.
I'll be back

36Volt

Day 2 wiring tracing, accessing, and testing. I will need a chiropractor when I'm done. Also learning how to spell spaghetti. I will post some pictures at some point to show some test points. The EBTCM pin 4 for example.
Since all this is accessing ESD sensitive units have my wrist ground on, I can see where one may create additional problems if you don't protect your circuits.
Radio dimmer resistors are in, but all this is while battery unhooked so no real way to know for sure until I stuff all this back together and hook back to battery.
Will put updates as I get there.

36Volt

Another thing that eats some time is I am doing drag tests to all the terminals of every connector I have encountered, there are many. This is the measurement of "drag" found when insertion and de-sertion of each contact to insure no resistance is being added by a soft or weak contact condition.

36Volt

OK Still not completely fixed BUT here's what I got so far:

FIXED:

My vette does NOT have electronic HV/AC.
The service bulletin "Hooked on Vettes" provided me is ALSO covered in the Factory Service Manual (FSM) I finally received.
The bulletin say on models with C68 electronic Climate Control, to hook switched power through resistors to 1 grey and 1 purple. - Did not work
The FSM says both climate control types, to hook switched power through resistors to 2 greys...... code 72 gone.
Non digital HV/AC is to BOTH greys only, least on mine, tried all combinations this worked.





UNFORTUNATELY NOT FIXED:
So, CCM code 41 (serial data loss) , ECM - ERR, and EBTCM H72 loss of serial data.
These are STILL occurring.

However, I have managed to get it so the engine appears to always start now, but have not really tested on the street just yet. At first, even in the shop I could run it long enough the service ASR light come on, the security light flashes with the system light begins, then when I shut it off, would not start.

Now, (at least while in the shop) when these lights occur, it does now start.

Here's what I did so far:

Read my new 2 book factory service manual cover to cover - both.
OHM test circuit 800 (tan) serial data destinations.
Exorbitant amount of vehicle disassembly to access everything (understatement).
Expose ALL harnesses, connectors and grounds to pertinant immediate effectable harnesses (between modules).
Visual state of health inspect all wiring.
Access to ECM, EBTCM, and eventually, reluctantly, the CCM.
Loosen and retighten EVERY GROUND. ( that I am aware of - there is many)
Unplug all connectors (in line and at modules), clean, "drag" test (snugged some loose) on ALL contacts.
Wiggle tests EVERY WIRE while running engine.
Repairs to all prior and current after market electronics damage to wires.
This was all a lot of work.

What I found so far:

Wiggle tests to wires while running found the White ECM A12 EST wire to ignition coil driver would kill the motor. Even not start until a position was found. It had been probed by a pin at one time and was corroded inside as result. This even traveled to the contact at connector A, rework was new contact, and segment of wire. NOTE the car NEVER DIED WHILE RUNNING like it did in this wiggle test, but noteworthy eventually ..... could.

Initially, prior to getting at the CCM, OHMs between the ECM and the EBTCM where .2 to .3 OHM. Between both D14 and D4 on ECM where .2 to .3 OHM.
BUT to the ALDL to these measured 7.8 K OHMs. Now had need to get at the CCM.

Did that: once the CCM was out, (this disturbed all initial wire bends) Now the ALDL has the same .2 - .3 OHMs to EBTCM, both leads to ECM and both leads to CCM, everthing has .2-.3 OHMS. ????

O-Kay, plugged EVERYthing in and started engine, the resistors mentioned above did clear the CCM code 72,
AND so far seams to start even when the all serial data codes exist.

Onboard CCM interrogation ALDL Terminal A to G has:
Module 1 (CCM) H and C41 serial data circuit loss of communication
Module 4 (ECM) as ERR
Module 9 (EBTCM) H72 serial data circuit loss of communication

now my M2500 will not talk to the car,
and when I interogate just the ECM ALDL terminal A to B - it flashes 12 (no code),

I also found the elusive splice S222, behind the friggen CCM in that massive harness but have NOT yet addressed its health, all the tape around the harness, and around the splice are so GOOEY, I have to clean before I can really see anything.

I also have opened the ECM, CCM, and the EBTCM and looked with magnification found nothing burnt, or loose, all solder is good and shiny. in fact all three where remarkably clean inside. This does NOT prove no issues but........

All the modules, even before dismanteling the car so far work perfect. Awesome engine performance, ABS/ASR work completely, and far as I could tell everything the CCM does is spot on. Even found all tests between 1.3 and 1.6 are live and functional.

This makes me reluctant to replace them yet.

ADDITIONAL Conditions:
There was a bunch of hacking to wires under the dash from prior aftermarket systems, and currently has a full blown autostart security, remote lock system.
I removed a dozen scotch locks and had to repair EVERY BIT OF IT, including the EST wire from the ECM failed the wiggle test.
Now all is high quality butt connected, soldered, with heat shrink, bout 30 of these repairs actually.

NOW FACT - Turns out - NONE of the damaged wires are ANYTHING to do with the serial data. No non serial data codes are present. But they may have had something to do with the no start when the lights started flashing, again, until I actually test drive, am not sure the no start is gone.

NEXT COURSE OF ACTION:
will be to extract the GOOGH off the splice S222 to the circuit 800 and resolder, also still some wire goes further toward passenger side from splice that Bends back toward drivers side check the bend.
Basically ensure the serial data circiut is solid. I may even replace this circiut with better grade wire.

Must say, this is definately more work to correct serial data communication than it was to rebuild the 700/R4 that was grenaded. another story another post I'll address later, 92, 93 Vettes are the ONLY cars got the 700R4 with the round connector on non electric shift monitoring 2nd and 3rd gear. Don't ever trade this for a rebuilt. rebuild your stock one ONLY.

36Volt

This is the dreaded Circuit 800 S222 Splice. This is in the worst possible place to have to access on the whole car.

36Volt

here it is with the tape slide away, S222 really gooey in there, also 4 wires go into harness only to be bend somewhere to comeback by.

36Volt

The dangers of SCOTCH LOCKS. Used all the time by aftermarket installers. These where carefully removed to not break more strands.<br/>Usually not this bad, but this happens when a smaller size blade is used than the size of the wire.......... is the case with these.<br/>Also the view of the accelerometer module for the ASR system.

36Volt

Wire repair from scotch locks.<br/>Tin plated barrel connectors with solder wetted in, and heat shrink - 0OHMs when done, and weather proof.

Cliff Harris

The splices I've seen seem to be crimped with a metal ferrule and then dipped in solder. They do seem very solid. The tape they wrapped them with seems to be related to duct tape, with a similar fabric backing. The adhesive gets gooey with time and turns into a big mess.

1stVetteFinally

Did you ever resolve this issue? My 92 LT1 is exhibiting the exact same symptons your's is/was.