Yes, code 15. I do have a temp gauge and it was reading normal. I am going to test the wires, end to end, before replacing the CTS. I ordered a replacement ICM, just to be safe. My spare is pretty old and I would not trust it for more than getting off a trail.
The temp gauge is driven by a different sensor than the one the ECM/PCM uses, so the dash gauge working doesn't mean the ECM is getting the proper temp. In fact, the Code 15 blatantly states that it is not receiving any signal whatsoever from the CTS, and has gone into a fallback mode. I'm not certain about the L98, but if it's anything like the later LT1, the fallback mode for complete CTS failure is...sadly, nothing other than throwing the code and, on an automatic, applying the TCC early. You should find the FSM for your '90 5.7 (L98?) and check the diagnostic page for DTC 15 to be sure. I only have the 1994-1995 5.7 (LT1) FSM, so that's all I can go by. But if in 1994-1995 the only thing that happens is throwing a code and applying TCC early, I would assume 1990 would be exactly the same. Doesn't make sense for GM to do something more advanced on a far more primitive computer system.
However, you are correct that a failed-low-temp CTS should not cause the engine to not run at all. It will cause it to run pig rich, and will cause it to never enter closed loop operation, but it should still run. If it does not run, something else is going on.
I agree that a total cutout sounds like ignition. Check all connections between distributor, coil, ICM, and ECM thoroughly. Again, the FSM can actually help you with the kinds of readings you can get with your multimeter to check each of these components. Or you could just throw parts at it, like replacing the ICM. But 100% start with the wiring since you already know that was a problem before. And if that CTS is any indication, it sounds like your wiring in general is suspect. Perhaps a rodent decided to have a snack. Best of luck.
1990 Corvette (Manual)
1994 Corvette (Automatic)
1995 Corvette (Manual)
Thanks for the reply. True that I have two temp sensors, one for the ECM and one that runs the gauge and electric cooling fan. Part of the problems I have been solving come from using a donor harness. It was in fairly good shape overall, but did have some issues such as the bare wires on the ICM plug. I plan to spend some time this week checking wires and voltages again and doing some data logging to see if I can see the intermittent temp failure. Glad to know the CTS would not cause the stalls. Didn't think so, but it's nice for validation.
Sharing my experience with bad coolant temp sensor (CTS) on my 95 LT1 -
My CTS failed low (constant, not intermittent), but not failed to the point that a code was set.
Flooded out the engine - wouldn't run when warm. Could start it with flood clearing mode (throttle to floor, no fuel) but would flood out after running a few seconds. Pulled the CTS connector to cause a hard failure. Started and ran well enough with code set and no CTS to get me home.
Testing without the sensor in play (and thus wiring as well) may help narrow things down.
Note my experience was with LT1, so others can chime in on any differences to your application.
Hope this helps -
Jim
1995 Caprice 9C1 LT1 - 4.10s, Dynomax Catback, K&N Cold Air Kit, Other Little Stuff
1996 Caprice 9C1 LT1 - 3.73s, Stock
To add to the above, Code 15 is triggered (at least on the 94~95 LT1) when the ECM detects CTS at -40F or lower for 2 seconds. On this application, that means CTS circuit at 100700 ohms or more (open circuit) for 2 seconds.
So if you're triggering Code 15, that means your CTS is intermittently reading essentially disconnected for 2 seconds or more. However, as Jim pointed out, it would be good to know what "temperature" is being reported for those times when Code 15 is not triggered as well. My bet is that it will read normal until Code 15 events happen, because the culprit is poor wiring causing a complete signal dropout.
1990 Corvette (Manual)
1994 Corvette (Automatic)
1995 Corvette (Manual)
Thanks for the info Jim. I had black smoke coming out the exhaust when the engine lost power. The black smoke could be the ignition cutting out or a super rich condition. I would not think that the intermittent CTS would cause what I was experiencing, but thinking of your failure experience I am not so sure now. However, I was getting the intermittent check engine light all day without runability issues, so... Hmmm.
I recorded the CTS plug positions at the ECU so I can run a continuity test while wiggling the wires today after work. I have a new plug I could wire in if the wires at the plug are faulty. If the wires seem good a new CTS is cheap.
Originally Posted by JimCT_9C1
sounds like you don't have equipment to data log? if not try to jumper the terminals of the CTS together. start engine, within ~30 seconds you should get a code 14. If you do, the wiring to ecu should be ok and the sensor is most likely at fault.
TBI codes explained with troubleshooting flow charts:
http://www.gearhead-efi.com/gearhead...c/TBIcodes.pdf
Hmmm. I like that idea as an extra troubleshooting step. I do have data logging capability as well as chip burning. I will try the idea you suggested though. Seems worth a shot just to prove I am getting what I expect. I'll probably try both open and closed to trigger each error.
On a positive note, I guess, I just finished testing the wires. I could not detect any issues in either the CTS or ICM wires. Wiggled like crazy everywhere I could and no change in continuity. Ordered a new CTS. ICM should be here Thursday. Ordered both the D1943A and the Police version D1984A. The D1943A will go in my onboard spares bin.
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