anyone know if the 1995 corvette should generate a PCM Error code (such as DTC 16, 41 or 42) if the ICM or Ignition Coil is bad ???  My 95 will crank but not start - there is no spark from the ignition coil to the optispark.  I have run the diagnostic checks from the service manual and it indicates one of these two components are bad.  But before I replace (since I cannot return the parts) I am curious why I would not have one of the above PCM error codes.  All those codes relate to ignition or low voltage.

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Lifetime Member #58
Our 82CE

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Not having a trouble code is common...it has to "see" a specific problem, for a specific amount of time, to set a code.
I'd say yer Opti-Spark is sparked out...

The ICM and the coil are one unit...if ya replace one, the other comes along for the ride!

The Opti-Spark sux...it's usually best to just replace the whole dang thing, and be done with it. The ones you can buy now have all the upgraded stuff in them, so they survive much better.
Stingrayjim had/has a hook-up on them, I think, as far as a good source to get them from.

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

One thing I might add is to check your water pump while your there. It is very common for the water pump to begin leaking and cause the distributer to get wet and fail.

The distributer is also a booger to remove. Good Luck Kerry!

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The water pump and optispark were new with the engine rebuild 10 months ago and since then, the engine has less than 500 miles.  If the optispark was gone, I should still have a spark from the coil into the optispark.....Right??

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Lifetime Member #58
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What th heck d'ya mean?

If there is an issue within the distributor(the opti-spark unit), the coil will not fire at all, depending on the failure mode. The optical wheel inside the distributor has to "trip", or signal the the PCM to fire the coil . Then the PCM signals the ICM(ignition control module) thru the EST(electronic spark control) by grounding the primary circuit that supplies the voltage to the coil. This collapses the coil field, which causes the coil to sparkle.
If I am a-reading you correctly, yer coil ain't firin, right?
Since the opti-spark was just recently replaced(which don't mean diddly anyway), how about the ICM/coil assy? Was it replaced at the same time?
I'd want to check and see if the PCM was grounding the circuit for the ICM, and if it is, then you know the opti is working, and the problem is most likely the ICM/coil.

If you have a test light, try this...
At the ICM connector, you should have a white wire, a white/black stripe wire, a pink/black stripe wire, and a solid black wire. The solid black is the ground for the module, so it should be grounded on the engine block.
The wire we want to check is the solid white wire. Remove the coil wire from the distributor, and place it close to something that will be a ground, like the block, or a bolt on the water pump. With the key "On", and your test light connected to a good ground, probe the white wire quickly...just a touch and release. IF the ICM is good, the coil should fire as you touch/release the test light to the white wire. If it does not, do it a few more times, just to be sure. If ya really want to be sure, grab the coil wire with your hand...you'll KNOW if the coil is firing...
If the coil does fire like that, then the problem is gonna be in the opti=spark unit, or the PCM. OR...the dang ground wire. Remember, it's STILL a Corvette, and grounds are important...

If you have a good voltmeter/digital multi-meter, you can monitor the white wire for a ground from the PCM while cranking the engine. Just set the meter for DC volts, and connect it to the white wire, and crank the engine. The meter should fluctuate from high to low voltage if the PCM is grounding the circuit as it should.

Did this just happen all of a sudden, or did it start runnin like crap, and then die?

another thought just floated into me haid...the tach filter could cause a no-spark, too, if it was grounded out...might see if you can unplug that, and give it a try...


oh yeah...one more thing....it's prolly a silly question, but has ya checked the fuses? A blown INJ fuse would also dis-able the ignition system...Adams' Apple2008-08-27 06:41:32

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Well, no loose wires, forced the ICM to ground with the good old paper clip trick .... and no spark ,  test light indicated a good ground on the ICM pigtail , also have a good ohm test of the wire from the PCM to the ICM .....The coil metal casing has rust on it and Joel says thats a good indication the coil has started to magnetize which prevents it from storing a charge ...... so, off to the parts store to get a new ICM and Coil $$$$ (well, not really, going to cheat and have my son get it from the Hummer dealer where he works....should save us a few coins at dealer cost ).  Will get the new parts in on the weekend and let y'all know how it works out.
Now while I wait, time to move over to the weatherstripping on the C3 back window.....then back to finishing the C4 interior.....always something


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Lifetime Member #58
Our 82CE

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 I'd keep in mind, the coil isn't going to fire if the opti IS NOT getting a signal to the ECM, which in turn signals the ICM to fire.

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Kerry's car isn't setting any codes, tho...it just won't fire. The "scratch test" showed the ICM/Coil isn't firing, pretty much eliminating the Opti as the source of the problem. IF the coil was firing during the scratch test, then we'd be looking at a PCM, wiring, or Opti issue. He tested the wire from the PCM to the ICM/coil already, and it was OK.
Opti issues will normally set codes, but a bad coil won't, in most cases, as the PCM doesn't monitor whether or not the plugs are firing. Adams' Apple2008-08-30 14:20:36

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

 I'll file that away for the future too Joel. That's why I enjoy reading your posts.  

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During Kerry's wait on the ICM module for kicks and giggles I would be taking each grounding points loose and inspecting, cleaning and replacing them.There are many and they should be better named as corrosion points rather than grounding points.

My last C4 opti / codes issues were like a witch hunt chasing through the codes / firing issues.
Each time I would clean some of the grounded areas it seemed to get better. (and I believe it was)

I finally traced the issue to an after-market security system that had been installed under the dash. I had not noticed it until on day I just happened to notice the light on the top of the dash was slightly different than others I had seen..... What if...? I disconnected it and found everything to be in working order afterwards. (then and now) Sooo, Bubba had struck in his quite undetected manner. Although I believe that it was no fault of his own that the after-market security system had died.

But what I did find that most likely had prompted the change in system I believe was the drivers door lock harness had been severed by the window track coming loose. Once I repaired the harness everything was back to normal working OEM condition. (OEM security system included)

Becuase in reality what I thought was an ECM then BCM problem was really something relative instead. I had a door lock keyfob problem that I had never considered to be relative.... but I was WRONG!

Moral of this story..... Every Freakin Thing in these cars is connected electronically to each other. Sooo if you may have to hunt deeper that the obvious to find the root cause. (Hence the saying "Thingz are not always as they seem!")

Hang in there Kerry my friend I lit a candle and placed it on my Corvette Alter for you my friend!

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Me too Kerry, I ll open that beer and wish ya luck..

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   "I Love all Corvettes! LifeTime Member #60..Terry"

Well, another long afternoon and no success.....changed out the ICM and Coil with new GM Delco..... but still have the same "Crank no start" problem.  From the look of the old coil and ICM, they were original and needed replacing.  The coil was rusted and the ICM heat sink silicon gel was all dried up to a powder.

Anyways....following the SM diagnostics, the ICM connector has 12 volts in on two wires, solid ground on the third and the fourth wire has good continuity to the PCM. 
Did the same checks on the Opti connector and everything is what the SM indicates. 
Also pulled the ignition coil wire and inspected -- it was new last year and still looks new....also tests out with 5300 ohms. 
Also did the SM test to jump the two "B" wires for the coil and test the "A" with the test light while cranking the engine.....this is suppose to cause the test light to flash, but NO FLASH....so guess what, the SM says either the ICM is bad or the ICM connector is bad -- no way all their tests said everything was good......HMMMMMMMMMMMM

Also cranked the engine and did Stingray Jims wire jiggle dance......no start.

Also rechecked every fuse with the DVM (just in case I had a sneaky non-visible break)....they all tested good

Here is the last thought.......the ONLY thing I did after the last start (Yah, I know, I just remembered it today as I was thinking through all the possible causes) was I got a keyless entry fob from Corvettes of Dallas.  (it was free as they did not have a working one when my son bought the car).  anyways, we tested it at the dealer and it programmed their 95.  When I tried to program my 95, I could not get the computer to enter into programming mode (light on the diagnostic center never came on).  I tried it several times but gave up thinking it needed the power door lock connectors plugged in (have all the door panels off to redo the weather stripping).

So my question is, could I have somehow disabled the start programming because I could not get into the keyless entry program???? I am grasping for anything now.

Tux, tomorrow I plan to connect the power door locks (power windows and rear hatch were always connected because I needed those) JUST TO SEE WHAT HAPPENS......NO WAY it should matter because I was driving it before with the door panels and power locks disconnectd.....but hey...its a vette with an attitude.

TUX....GET BUBBA OUT OF HERE.....I found his after market security under my dash also a few months ago.   A key in a cylinder with two wires going somewhere.  anyways, the car worked with it but who knows now.

Thanks everyone for your continued suggestions  (and no, I am not frustrated enough to pull the Opti or replace the PCM .... yet)
Reds82CE2008-08-31 16:57:16

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Lifetime Member #58
Our 82CE

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Uh oh....you may have a CCM that took a doo-doo.
I just thought of that, since you mentioned the key thing. The Central Control Module, if bad, WILL give you a no start, AND, it will not let you program the key/fob for the security system. But then...it would also keep it from cranking, too...
You may have disabled the starting thingy when you attempted the re-program for the key...might as well go ahead and plug all that crap back in, and give it another shot.
I had a '96 at the shop that had pretty much the same issue, and testing on it showed the CCM was shot. We got a new CCM and installed it, but STILL had to send it to the dealer to get the danged key programed.
Hopefully yours is not like that...

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Joel Adams
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Would a bad battery in the key fob do this??

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   "I Love all Corvettes! LifeTime Member #60..Terry"

Kerry, your skeerin me... I had tried to put this C4 episode outta me lil pea brain an now it's s-l-o-w-l-y coming back (OUCH).

Okay did your car every so often happen to lock itself? That is the one thing I fergot to mention. All of your symptoms are the same as whut mine were (cept that one).

I also borrowed a friend keyfob to program the car to see if it was gonna werk prior to buying a keyfob. Primarily because I I was struggling with the "other" electrical issues simultaneously. Like yours it wouldn't work. That is how I found the severed harness. I couldn't figure out why is wasn't working until I removed the door panel and said " Oh my God..... ain't that just grand!"

I can tell you that in 94 they made the harness specific for that car. Finding a used one was impossible so I painstakingly repaired the old one 1st rather than donating $150.00 to the stealership to see if it worked. Fortunite for me it worked fine afterwards.

I believe that you will be able to locate a used harness coil for your car with success if you find that yours happens to be damaged as well. I might note here that I had no window problems (up / down) to indicate something had gone wrong. It did appear though that the root cause of the harness coil having been severed was it had came loose and manage to slide over into the tract.

Candle still burning Bro......


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If I remember right, when programing the key/fob, it will cycle the door locks, so ya might need all the stuff connected.
Does your key have the little resistor pellet in it?

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Yes, the key has the pellet, but both sets of keys give the same "Crank-no-start".

Reconnected all the door electrical connections....still no change.

So, I checked all the codes in the computers again, CCM 1.2, 1.3, 1.4.  all these settings are normal and indicate the CCM is communicating to all the sensors correctly.  In 1.3 mode, I could see the CCM turning on/off sensors/lights.  So this tells me the CCM GROUNDS ARE GOOD.  Also verified again there are no stored DTC codes in the PCM/ECM/ABS/TCS/DERM. 

Back to looking for bad connectors by doing a continuity test on all the wires....someone tell me there is an easier way
Reds82CE2008-09-01 14:18:04

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Lifetime Member #58
Our 82CE

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All my grounds from the PCM are good.  Pulled the PCM connectors off, connected the test light to each ground pin and light came on.

Also did a continuity test on the Opti 4 wire connector back to the PCM:
B2 - Low Resolution Signal Input was 3.4 ohms
B3 - Distributor Reference Low Signal was 2.0 ohms
B14 - Distributor Ignition Feed was 0.6 ohms
B20 - High Resolution Signal Input was 0.8 ohms

I can't find anywhere in the SM that tells me if B2 and B3 should be that high....ANYONE KNOW????

According to the SM, I still need to test the following which causes a crank no start:
B2 - Low Resolution Signal (but this should set DTC 16)
B3 - Distributor Reference low signal (No DTC set)
B5 - Ignition Control (should set DTC 41 or 42 and I installed a new coil an d ICM so can rule this one out)
B14 - Distributor Feed (No DTC set)
B15 - PCM Battery Feed (No DTC set and has something to do with the Oil pressure switch)
B30 - PCM Ignition Feed (No DTC set)

The  test for B2 is "TEST CONNECTOR 'A' DISTRIBUTOR 'A' " and B3 uses "D"..............IS THIS JUST A CONTINUITY TEST??? Same as I did above?


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Lifetime Member #58
Our 82CE

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B2 & B3 appear to have high resistance. As far as I know, they should read the same as the other two wires, UNLESS there is a "filter" in-line on them. I don't have diagrams here for the '95, but I can get what I have at the shop tomorrow...

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

 As the owner of an Lt4 with 50k and starting ton leave a small Puddle of Antifreeze I have been fowwoling this one with great Interest. The big Waterpump-Optispark-Plugwire Replacement is just around the corner. All the advice given above is way above my Head so all I can do is agree as it all makes sence to me. The only thing I can add is to give Gordon Killebrew a Call I assume If you guys know as much as you do you know who He is. For those here that don't He Teach's Troubleshooting Class for C4's. He is the Guy who rewrote the Shop Manuels for GM. If a 95 won't fire cause the left Rear Tire is low and the passenger Seatbelt is undone wile the Hood is open He is the Guy who will know. www.gordonkillebrew.com 

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My Car...PIC 1     PIC 2

Well, still no start.....BUT I DID FIND OUT WHAT BUBBA WAS UP TO......

they bypassed the PassKey circuit in the steering column and sent the white/blk and ppl/wht wires into a separate key cylinder (with key) tucked up under the dash.

When I reconnect the steering column key I get a CCM DTC 53 -- "Circuit Open or Shorted to B+"  .....

So, instead of fixing that problem, bubba just bypassed with a dummy key so any key in the ignition (as long as it was cut close to the original key) would start the car.

The short/open must be in the steering column key cylinder, so I wont be in any hurry to take that apart.


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Lifetime Member #58
Our 82CE

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Whuuuut?
Daaang...Bubba's gittin mighty goldang crafty, ain't he?

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

 So what about just replaceing the Steering Column itself and not messing with the Lock. Might be easyer in the long run. As all 93-96's C4's should have the same Options in column as far I can tell they should't be worth that much Used. If You did do this and ended up with a Black Steering Wheel in near new Condition I'd be interested in Buying it.

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My Car...PIC 1     PIC 2

Another evening and still no life in the engine.....

BUT..... BIG WIN.... fixed Bubba's hack job .... took apart the connector for the wires from the steering column resistor check circuit and re-soldered the connector and now it works.  reads 11.7 ohms with the key in .

Re-tested the ICM wires and they are all good
Re-tested the coil wires but still no signal to energize the coil

I still dont understand how the opti could just quite but I am about ready to rip it out and look at it unless someone/anyone has any other ideas


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Lifetime Member #58
Our 82CE

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You've got mail!
A problem with the anti-theft system would keep it from cranking, and the injectors from firing...yours is cranking, so I have to think the anti-theft is a moot issue, other than fixing the bubba stuff.
One thing do come to mind...what did you actually find wrong with the column connector for the ign switch? Broken wire, terminal, or whut?
If all you did was solder the terminals, and put them back in the connector, it's possible that the terminals on your ICM/Coil are also corroded enough to create a no start, even thu the voltage/resistance checks are good...just an idea.
I see this a LOT on cars at the shop...I'll wind up opening up the terminals and removing the wires, cleaning both the wire ends and the terminals, and the re-crimp, and solder the terminals back....fixes most of them...

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Wires at the connector "looked" good but the insulation had been pulled back about a quarter inch on both wires.  No signs of rust.  I just cut the wires, opened the terminals, soldered the wires to the terminals and put the connector back together.
I tested the key chip resistor, then tested the circuit without the key (no continuity), then tested with the key in and got the resistor ohms same as on the key.

I will do the same for the ICM, Coil and Opti connectors.  lot of work but still easier than pulling the opti



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Lifetime Member #58
Our 82CE

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Well, after more tests, I think I will pull the optispark.  However, if it is chewed up inside (which I suspect) then I have a bigger problem.  Last year when the engine was rebuilt they assembled the engine with the wrong cam shaft bolt (too long) and that was the cause of the opti's being chewed up then.  The engine rebuilder gave me most of my money back which went to the dealer to install the old cam bolt and new opti.  Now I wonder if that old bolt was not the correct one and was putting pressure (although less than the first bolt) on the rotor.  Makes me wonder since the car only had a few hundred miles on it since the rebuild.

So, if the opti is chewed up, I will have to pull the cam shaft out and replace it a new shaft/bolt.....GM does not have any bolts.

What a mess.....Don't think I will replace with another opti....instead may look at one of those bolt on replacements or a crate engine.

Any suggestions on a crate engine that is a direct bolt-in and does not have an OPTISPARK?????


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Lifetime Member #58
Our 82CE

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 Sorry. Red I don't understand how a camshaft bolt can damage the rotor. On my LT-1, the only common surface between the cam and the opti is via

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