and do the code read with the climate control too. 
sensor mystery
Thread Starter
Instructor
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From: Savannah GA
sensor mystery
I recently purchased a 95 C4 base coupe. The car runs great but has an issue which has me somewhat puzzled, partly because I have taken the car to three auto parts stores to have the codes read and all three have gotten communication error messages.
The issue is that any time the engine revs above idle, the cooling fans immediately kick on, as does the "check engine" light. This happens even when the engine is cold. Car drives fine, and after a few seconds of idling at a light, the fans and the dash light go off. As soon as I step on the gas, both come back on.
I did have a broken connector on the coolant temp sensor on the front of the engine and thought maybe this was triggering some type of fail-safe condition with the fans. Changed the sensor, still have the fan/light situation. All gauges read normal.
Any suggestions?
Thanks.
Eric
The issue is that any time the engine revs above idle, the cooling fans immediately kick on, as does the "check engine" light. This happens even when the engine is cold. Car drives fine, and after a few seconds of idling at a light, the fans and the dash light go off. As soon as I step on the gas, both come back on.
I did have a broken connector on the coolant temp sensor on the front of the engine and thought maybe this was triggering some type of fail-safe condition with the fans. Changed the sensor, still have the fan/light situation. All gauges read normal.
Any suggestions?
Thanks.
Eric
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the cooling fans always kick in with service engine light? have you tried the paper clip method to pull codes?
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They (auto parts stores) would get a communication error because they're trying to read the connector (ALDL) with an OBD2 scanner and while the connector is 16-pin like an OBD2 it's an OBD1 car. Here's a good read for you and you can accomplish this yourself easily. Pay attention to only '94+ information and the pins that require being "jumped" to initiate the check.
http://tech.corvettecentral.com/2011...trouble-codes/
http://tech.corvettecentral.com/2011...trouble-codes/
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Thread Starter
Instructor
Joined: Apr 2015
Posts: 153
Likes: 12
From: Savannah GA
They (auto parts stores) would get a communication error because they're trying to read the connector (ALDL) with an OBD2 scanner and while the connector is 16-pin like an OBD2 it's an OBD1 car. Here's a good read for you and you can accomplish this yourself easily. Pay attention to only '94+ information and the pins that require being "jumped" to initiate the check.
http://tech.corvettecentral.com/2011...trouble-codes/
http://tech.corvettecentral.com/2011...trouble-codes/
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I didn't see mentioned that the connector to the ECM temp sensor had been replaced so we might have wanted to add a step in here before attempting to read any information from the car. Disconnect the battery negative cable to "reset" the ECM etc. Required? generally
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Instructor
Joined: Apr 2015
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From: Savannah GA
OK... back from the garage. I found 3 codes, all preceded by "H". If I understand the article properly, this means they are History, not Current codes, correct? These are the codes and my interpretation based on the above article...
Module 1, H-72: LCD dimming circuit open or shorting to ground.
Module 4, H-26: EVAP canister purge solenoid circuit.
H-15: Engine Coolant Temp sensor.
The temp sensor seems to make sense due to the broken connector on the old sensor. Would the H-72 code refer to a dim IP readout? Mine works but is very dim and hard to ready under many lighting conditions. I still can't make the link to the fans. Am I misinterpreting something?
Module 1, H-72: LCD dimming circuit open or shorting to ground.
Module 4, H-26: EVAP canister purge solenoid circuit.
H-15: Engine Coolant Temp sensor.
The temp sensor seems to make sense due to the broken connector on the old sensor. Would the H-72 code refer to a dim IP readout? Mine works but is very dim and hard to ready under many lighting conditions. I still can't make the link to the fans. Am I misinterpreting something?
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OK... back from the garage. I found 3 codes, all preceded by "H". If I understand the article properly, this means they are History, not Current codes, correct? These are the codes and my interpretation based on the above article...
Module 1, H-72: LCD dimming circuit open or shorting to ground.
Module 4, H-26: EVAP canister purge solenoid circuit.
H-15: Engine Coolant Temp sensor.
The temp sensor seems to make sense due to the broken connector on the old sensor. Would the H-72 code refer to a dim IP readout? Mine works but is very dim and hard to ready under many lighting conditions. I still can't make the link to the fans. Am I misinterpreting something?
Module 1, H-72: LCD dimming circuit open or shorting to ground.
Module 4, H-26: EVAP canister purge solenoid circuit.
H-15: Engine Coolant Temp sensor.
The temp sensor seems to make sense due to the broken connector on the old sensor. Would the H-72 code refer to a dim IP readout? Mine works but is very dim and hard to ready under many lighting conditions. I still can't make the link to the fans. Am I misinterpreting something?
and look for the climate control test.
Thread Starter
Instructor
Joined: Apr 2015
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From: Savannah GA
Disconnected battery for approx. 15 seconds and re-checked...codes still there. Is that not long enough for a reset?
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From: Savannah GA
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From: Wake County NC
This works on my 92 for clearing the codes.
Don't know if it will work for yours.
4.7 clear ECM fault codes
Press the TRIP RESET button until 4.0 is displayed in the module number area. Then press the TRIP/ODO button until 4.7 is displayed in the module number area. Press and hold the ENG/MET button until “—“ is displayed. This will clear any ECM codes. After “—“ is displayed turn the key off, wait ten seconds turn the key back on and check for any ECM codes.
Press the TRIP RESET button until “1.0” is displayed in the module number area. Then press the TRIP/ODO button until “1.7” is displayed in the module number area. Once there, press and hold the ENG/MET button until “—“is displayed. This will clear any CCM codes. After “—“ is displayed, turn the key off, wait ten seconds, turn the key back on and check for any CCM codes.
Don't know if it will work for yours.
4.7 clear ECM fault codes
Press the TRIP RESET button until 4.0 is displayed in the module number area. Then press the TRIP/ODO button until 4.7 is displayed in the module number area. Press and hold the ENG/MET button until “—“ is displayed. This will clear any ECM codes. After “—“ is displayed turn the key off, wait ten seconds turn the key back on and check for any ECM codes.
Press the TRIP RESET button until “1.0” is displayed in the module number area. Then press the TRIP/ODO button until “1.7” is displayed in the module number area. Once there, press and hold the ENG/MET button until “—“is displayed. This will clear any CCM codes. After “—“ is displayed, turn the key off, wait ten seconds, turn the key back on and check for any CCM codes.
Thread Starter
Instructor
Joined: Apr 2015
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From: Savannah GA
I don't think this will work with my climate control...btw, ac fuses are good. However, AC compressor doesn't turn on...possible related issue? Haven't had a chance to investigate this.
Last edited by bigtoys; Jun 10, 2015 at 08:27 PM. Reason: add further information
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You have to disconnect the battery for about 30 minutes to clear the codes. I had problem with the water pump coolant sensor. I replaced three of them until I realized it wasn't getting a good ground. So I added a ground wire from the factory harmes. Been working fine ever since.
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