Parked my '93 (6-spd totally stock LT-1) in the garage at night - next morning it won't start. Turns over great, everthing seems to work but this - "LO" light steady in display for 5 - 7 seconds, then changes to flashing "SYS" for about the same period. "SECURITY" lights steady with "LO" and flashes with "SYS". "Service ASR" and "Service Engine Soon" steady in DIC.

Shorted terminals A and B at DLC but it wouldn't throw a code, not even '12'. Analogs worked, digitals did not. Gave up to go read manual.

Next morning, ready to test, but it fires right up. Quickly checked for codes and only get the '12' - nothing stored. Went for a drive and everything worked fine for about 20 miles and two intermediate stops then restarts, then evertything stopped working. I limped home carefully, same symptoms as before except is was running (barely).

Trouble shot to the best of my limited ability, up to removing connector A from ECM. Couldn't figure how to short "ckt 420 to B+" (best of my memory) so called it quits for then. Symptoms same as before - turns over really well, no fire, no gas smell - nothing.

Anyone with experience who can point out a simple no-brainer test I'm forgetting (battery connections fine), or am I reduced to flat-bedding it to a shop? TIA for any advice. Thanks,

 

On 90-93 you can short terminals A to G on ALDL with a paper clip and turn key to ON position without starting motor to display codes directly on digital speedometer.



It will show --- then module # then codes associated with that module then --- when done. If for some reason the CCM cant communicate with other computers then "ERR" will display.

Mod 1 = CCM
Mod 4 =ECM
Mod 7=ABS and ASR

Example:
You place paperclip inbetween the A and G then turn key forward and look at digital speedo display and you see
---M1, H32,22,23.M4,,,M7,,,---

This translates 3 ECM codes, NO CCM codes and NO ABS,ASR codes.

The ECM Codes for this example would be "H'' 32 (H is for history meaning it's a stored code and problem may be corrected). 32 is for EGR. Then 22 is for TPS. Then 23 is IAT low. Then --- says thats all.

Each code will display for 3 seconds then move on.

You can repeat the sequence by turning key off for 5 seconds then back to on (motor still off).

I hope this helps. If you get any codes let me know and I'll tell you what they are if needed.

Dave

 

Dave . . . YOU"RE THE MAN. I have not come across that helpful tip in the manaul, but will certainly try it tonight. I'll post the results, the fix attempt and the results if this works for me.

Many thanks for the response / advice.

 

Would like to know what you found after running CCM diagnostics. I have identical problem with H41 (serial link between CCM / ECM) and H72 (same thing I believe). I have also experienced fire up and immediately dies. I cleared codes per service manual and by luck it started. But I get same codes with "check ASR" lit up.

I would like someone to say that it is likely ECM bad loading down serial link...then I won't have to dig under dash to find the CCM check wires, etc.

So please tell your resolution and/or ideas. If you need explicit directions for clearing codes, e-mail me and I can provide them right out of service manuals.

Buck in Virginia

 

This is just too weird. My '92 is showing the EXACT same symptoms.
The codes that it set were H41, H65 (right bank O2 sensor, rich) and H72. Oh, and the "check ASR" light...

 

You're welcome swifty. Let us know what you find.

Remember guys the "H" means it's a history code and not necessarily a current condition. A previous owner could have fixed a problem and not cleared the code or condition may have changed.

Now if your having obvious problems now then it's likely just showing "H" because the key has been on and off a few times since code was initially thrown.

If I get "H" codes I will usually make note of them and check that condition and then clear them by unhooking the negative battery cable for 60 seconds and then reconnecting battery and making a test run to see if SES light comes on and code(s) are repeated and/or conditions repeated.

Nimrod and Rubydog, Not sure about all your conditions but my code list shows the 72 your both getting to be "Gear selector switch fault (start lockout)"

Hope this helps.

 

Thanks Dave. I cleared the codes last week, so these are my "H"s. The car has been acting wonky lately, but it actually quit on me last saturday. Got it home, put it on the battery charger and it started right up. I'm now wary of taking it out more than a few blocks.
Anyway, my Haynes manual says that for a code 72 to "check the connections at the TCC solenoid and Park Neutral switch". These are auto tranny items, right? My car is a six-speed...
Thanks again.

 

If you see the check ASR light come on , pull out key and re-insert., turn on but not engine. May take two or three times but light will go off. When it does it will start. This will prevent any embarrassing long start ups.

 

I have an automatic so I'm no 6 speed guru by any means but I think there's a clutch start safety switch that wont allow you to start car in gear unless clutch is engaged. May be the same thing as park/neutral switch on Automatic.

Maybe someone with a 6 speed will chime in.

 

I'm still chasing same problem. ASR ligt comes on, sys & security light blink every 15 seconds or so, sometimes no start! CCM test: Module 1 CCM, H41 & H54 - serial link CCM/ECM Module 9 ABS, H72 - serial data link malfunction. Disconnecting battery does not clear CCM codes; For example to clear code 72, you must run CCM test, Hit trip reset until 9 comes up, then trip odometer until 9.7 comes up, then hit engine metric.

I get a no start if after turning on key, the sys starts flashing immediately...FEDS fuel enable not set I believe. Can't run my Ruby like this but don't want a $1,000 dealer bill.

What next??

Have service manuals, they say to dig into wiring under dash...God help me. Someone said to try unhooking ABS unit in tub hehind driver seat and see if problem goes away. Anybody tried that yet?

Buck in Virginia

 

Buck,
Thats a bugger for sure. I've never dealt with that one before but I will say I doubt the "no start" condition is related to the ABS/ASR.

When you say "no start" does starter turn over or click?? If not you may also have a VATS condition hence the security flash. It could also be something as simple as starter or starter solenoid going south, which can be intermittent for a while before totally dieing.

Wish I could offer more and I may be wrong but I think the no start is unrelated to ABS/ASR. If I'm wrong someone please feel free to correct me.

 

I recently had this same prob with my '93. I couldn't even clear the codes in the CCM using the paper clip deal. Replaced a few things, checked all my grounds and finally replaced the ECM (with a known working one). Hooked up the battery, bumped the key, and it has fired up ever since with my gauges and all working. No more codes, no problems, and the CCM can be cleared through the diag method. I checked everything I could think of, I even pulled the CCM out to check all of my wiring and connections before replacing the ECM. Good luck and maybe this will solve your problem. I wouldn't put much faith in a remanufactured ECM however, see if you could possibly try a friends ECM, or locate one out of a running car.

KC

 

Shorted ADL leads A & G, and I got the following displays:

1 C41
1 H41
1 H72
- - -
4 ERR
7 ERR
9 H72
- - -
1.0

This didn't look exactly like I was expecting from your post, Dave, so I repeated it and got the same results three times. I did not see a " - - - " in the beginning, the numbers (1, 4 7, 9, and the final 1.0) were small and near the bottom of the display, while the "lettered" codes were larger and higher in the window.

I delivered it to a mechanic friend on a rollback at noon. I just spoke to him - said he put a Tech1 on it and got airbag codes, among others. He thinks it is the fuel pump (didn't specifically say he got that code). He sprayed fuel in the air intake and got it to fire, so he is convinced that is the problem. Not knowing any better I let him run with it. He's not a bad guy, but he's not a Corvette specialist, so I don't know how this is going to turn out. I'll certainly post the results.

 

Actually, now that you mention it the --- is for in between modules and at the end.I was running on memory and thought I rememberd it also starting off with --- . I think that the only time it starts with --- is when there are no codes and in that case --- is all that displays.

I dont have a 93. I have a 90 but my literature says that 90 through 93 the module #'s are the same and what I gave you. The module 9 was for 1994-6 and is ABS/ASR. It says for 1996 only the module 7 is RTD module. The 1 and 4 are still CCM and ECM (or PCM FOR 94-96).

Its hard to type exactly what it will look like on the digital speedometer. I guess I should have specified that the module # would be smaller and below.

Be it as it may, regardless, here's how I read your results.

1 C41=(current) cylinder select error circuit
1 H41=(history) cylinder select error circuit
1 H72= (history)gear selector switch fault
- - -
4 ERR= CCM cannot communicate with other computers in this case the ECM
7 ERR=CCM cannot communicate with other computers in this case ABS or ASR or since you apparently have a module 9 then possibly RTD
9 H72=(history)gear selector switch fault.

It's confusing to me that you have a module 9. Which should be for later models with the 16 pin OBD-II version of the ALDL. In which case you would short pins 4 and 12 to read codes on speedo.

I wonder if you have a newer computer with the earlier ALDL or if the general was doing some weird transition between the two at the time yours was built. The general has done stranger.

Anyway, If I were you I would take this one to a corvette specialist not some nice fella that sprays fuel in the intake to get her started. He may mean well but I somehow doubt he posseses the skill to work out your troubles. There's a reason your not getting fuel and it's because the fuel pump probably doesnt run unless the gear selector switch is working proper. I'm no expert so I dont have all the answers but my advise is that you take it to someone that knows C4's.

Best of luck to you.

 

About the H72 code, my 93 service manual is confusing or maybe I'm just confused. In the ABS section, when you get the DTC code in test 9 of CCM, it shows a flow chart concerning a serial link problem. In another section, DTC 72 means something else.

I have decided to take a chance and get a new ECM tomorrow since I think this is a heat related problem. Immediately after turning the key, I get the sys and security flashing and car will not fire. Then I put an ice pack around ECM and tried it and no codes (sitting in garage). If I am correct about a bad ECM loading down the serial link, then this should solve the problem. Otherwise, I will have wasted $100. Will let you know what happens!

Buck in Virginia

 

My no start is as follows: If I turn on the key and sys and security flash immediately, the engine turns over and fires off only to die after about 2 seconds. I believe that the H54 is fuel enable. If the CCM can't talk to the ECM, it does not send a fuel enable signal, hence no injector action after the initial burst. (There is fuel pressure on the rail at this time.)

But if I am lucky and turn on the key and get a temp reading vice the flashing, it will fire off OK. The way I read it, once FEDS enable is established, the CCM will not cut it off when the CCM/ECM link goes south. For me, this is as I leave my driveway...I start getting sys. But the car runs fine till I get it home. But I dare not cut it off away from home!

As I said in another posting, I have decided to try a new ECM. Hopefully, the ECM serial circuitry is loading down the serial data line and causing this problem. I just hate to think about tearing into the CCM or the antilocking brake system (which as I understand it are all on the same serial link.)

Will let you know after I figure get the new ECM and figure out how to get those big connectors off!

thanks for all of your comments!

Buck in Virginia

 

Just wanted to let you guys know; Zip, NAPA, and Mid America have no ECMs for a 93. You must send in your old ECM and they will refurb it...wait about a month. Advanced Auto has them for over $300; too much when I don't even know that is my problem.

Swifty: Have they diagnosed your problem yet? The fact that she turned over when the tow truck guy sprayed starter fluid in is still a sign of no injector turn on. If yours turns out to be ECM, I may have to spring for a $300+ unit from Advanced Auto. Or take it to dealer!!

Buck in Virginia

 

That sucks Buck! I tried ebay and found this one for a 90-91 for $45
http://cgi.ebay.com/ebaymotors/ws/eB...spagename=WDVW
But no 93. Perhaps you should post in C4 parts/wanted or C4 & C5 parts. Also you could check all the Corvette salvage yards and buy from someone who has a return policy if it doesn't work. There's alot of wrecks where the ECM is not damaged I'm sure.

Good luck in your search.

 

UPDATE . . . mechanic installed new fuel pump and it fired right up. It runs VERY rich (stumbling, smoking, etc.). He is now going to check the O2 sensors to see if they're clogged up.

Haven't I heard that the computer has to "re-learn" settings when you change something in the air-fuel mixture mechanics? I'm thinking the old fuel pump wore out gradually, causing the computer to give longer and longer injector cycles of lower and lower pressurized fuel. Now that it's back up to full pressure with the new pump does it have to run a while to lean-back on the injector pulse time? Just a stab in the dark - but worth a question.

I'll update as I learn more. My beautiful yellow toy sure looks lonely up on a lift with the back end sooty - and me stuck with the DD and a nice, sunny weekend coming up.

 

Park the car in hot place and see if the problem pops up again.
Someone mention to me a while back that the ECM's on 92/93's cause a starting problem when hot. Maybe its a myth but I park in shade whenever I can.

Also I believe it takes about a 20 minute drive for your eCM to re-learn the new settings.