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Cooling fans never turn off

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Old Oct 2, 2008 | 04:39 PM
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Default Cooling fans never turn off
1994 LT1 - Both cooling fans are always on and do not shut off when the motor is running.

Bad relays? Are they located on the drivers side of the radiator shroud?
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Old Oct 2, 2008 | 04:45 PM
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Change them all! You haven't given us enough info to make a decision.
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Old Oct 2, 2008 | 04:55 PM
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Originally Posted by MK 82
Change them all! You haven't given us enough info to make a decision.
Cooling fans. Always running. When motor is on. They never shut off.

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Old Oct 2, 2008 | 04:58 PM
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Make sure the A/C is off and check for DTC's, some will cause the fans to run.
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Old Oct 2, 2008 | 05:01 PM
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Originally Posted by toptechx6
Make sure the A/C is off and check for DTC's, some will cause the fans to run.
A/C is off.

Only codes are:

H43 - I already replaced the knock sensors, so still trying to figure that one out. Possible PCM?
H63 in module 9
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Old Oct 2, 2008 | 05:16 PM
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Originally Posted by formul89
A/C is off.

Only codes are:

H43 - I already replaced the knock sensors, so still trying to figure that one out. Possible PCM?
H63 in module 9
If your 94 is the same as my 93, module 9 should be ABS, DTC 63 would be Valve Solenoid Relay Malfunction, that should not turn on the fans but the 43 could do it.
In my experience ALL codes are history codes, I have never seen one listed as current even by disconnecting a sensor with the engine running.
The PCM is a possibility but I would check the sensor wiring carefully before condemning it, or borrow a PCM if possible, good luck.
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Old Oct 2, 2008 | 05:23 PM
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Originally Posted by formul89
Cooling fans. Always running. When motor is on. They never shut off.

OK since you didn't get the hint. Is the AC on? What is the digital temp? Some trouble codes will make the fans run. Get it?
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Old Oct 2, 2008 | 05:29 PM
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Originally Posted by MK 82
OK since you didn't get the hint. Is the AC on? What is the digital temp? Some trouble codes will make the fans run. Get it?
A/C - off.

Digital temp stays constant at 203-206 after replacing radiator and flushing coolant with fans running.
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Old Oct 2, 2008 | 05:31 PM
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I would ask if you have the schematic, but I think I know the answer. When did you discover this?
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Old Oct 2, 2008 | 05:42 PM
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Originally Posted by MK 82
I would ask if you have the schematic, but I think I know the answer. When did you discover this?
I found a post here with the schematic.
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Old Oct 2, 2008 | 05:50 PM
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Originally Posted by formul89
I found a post here with the schematic.

There you go. Have fun with your test light and multimeter.
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Old Jul 12, 2009 | 12:54 PM
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Got the same error. I just have code H43, which is not always on. Only when the SES light comes on, the motor turns to rough idle and fans stay on. Gotta check after all, the optispark.
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Old Jul 12, 2009 | 04:43 PM
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Originally Posted by shadowskill
Got the same error. I just have code H43, which is not always on. Only when the SES light comes on, the motor turns to rough idle and fans stay on. Gotta check after all, the optispark.
For a 1994, H43 is 'knock sensor circuit' (either CKT 496 becomes open or shorted to ground).

Based on the original poster, it would seem that this code can cause the fans to continue to operate (albeit not mentioned in my 94 FSM).

Suggest clearing the code and checking the knock sensor(s) wiring (damaged, bare, touching manifold).
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Old Jul 12, 2009 | 05:07 PM
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I kept getting the H43 code intermittently when it would go into closed loop.

Figured out the driver side o2 sensor was bad and swapped in a new one. I have no idea why it was a knock sensor DTC, but no more codes.

Problem solved.
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