The subject vehicle's radiator cooling fan doesn't come on even when the vehicle is starting to overheat. I have taken the following troubleshooting steps:

1. Performed diagnostic test and no fault codes are present.
2. Grounded pin E8 of C3 connector going to PCM. With ignition in "ON" position, the fan control relay energizes and the fan runs. This should confirm that all wiring in the fan circuit including the relay is good. I also verified by checking continuity of the Grn/Wht wire from the relay to the PCM, the Blk/Red wire from the relay to the fan, and the Brown wire from the fuse panel to the relay to make sure not were shorting to ground.
3. Verified that the Brown wire coming to the fuse panel to the relay is hot as soon as the ignition is turned on.
4. Verified that the Red wire coming to the relay is hot at all times.
5. Verified continuity between the Yellow wire going to the Engine Coolant Temperature sensor and pin E16 of C3 going to the PCM.
6. I removed the Engine Coolant Temperature sensor and checked its change in resistance as I heated it from room temperature to boiling in water. With the Ohm meter set in the x10 position, the reading varied from 165 (room temperature) to 24 (boiling) while the tip was fully emersed in water.

My daughter has also stated that her air conditioning is not working. I know that the fan is supposed to run some of the time (if not all of the time) when the A/C is in the "ON" position regardless of whether the compressor is engaged or not.

The vehicle also has a coolant leak that I am having a very difficult time tracking down. I first noticed it when changing the oil and saw a drop of coolant suspended from the plastic shroud under the back of the engine/front of the transmission bell housing. I have not been able to see any signs of leaking around the intake manifold or cylinder heads from above.

Any ideas related to these issues is greatly appreciated.

Best Regards,

Ted

 

I just confirmed that the fan will come on with the A/C turned on and the connector going to the Fan A/C Pressure Switch disconnected. This connector has a Dark Blue Wire going to it that has 12V going to it at all times once the Ignition is turned to the ON position, regardless of whether the engine is running or the A/C is turned on. It also has a Black/White wire which always has continuity to ground.

What really has me confused is that if I check continuity to ground for the Dark Blue wire when the ignition is shut off, it shows to be grounded. I don't understand how it could show 12V with ignition on, but continuity to ground with the ignition off without a fuse blowing or something burning.

Best Regards,

Ted Allen

 

With the engine cold, I measure 3,000 Ohms between pin E16 of C3 and pin B6 of C1 at the PCM connections. I believe these to be the connections from the Engine Coolant Temperature sensor. I have confirmed that by checking continuity between these pins and the coolant sensor connector end. Also, neither wire is shorted to ground.

Best Regards,

Ted Allen

 

You have verified that a good portion of the fan system works properly. The A/C pressure switch signals the ECM that the fan needs to be turned on. With that connector disconnected and the fan working it proves out the ECM, relay, fusable link, fan, just about everything.

The '92 calibration turns the fan on at 226 F and off at 219 F (108 C & 104 C). This is controlled by the coolant temperature sensor (CTS) at the front of the manifold. Which you have checked.

It may be that the CTS is off a little, and/or the temperature gauge is off. The gauge is controlled by a different sensor. I've also found that the CTS connector pins and connector tend to corrode a little. This can throw off the reading.

Best bet is to put a scan tool on it and observe the temperature that the ECM is seeing. Do it after the car has sat overnight. Both the IAT and CTS should read the same, and be at ambient temperature.

Then start the car and observe the CTS reading. Once it reaches 108C the fan should come on.

For the water leak: check right below the throttle body. There is a fitting that protrudes from the manifold that likes to corrode. Same for the water pump gaskets. Then tend to deteriorate.

A/C may be empty. Is there a good line of oil under the hood from the front of the compressor? If so needs a new shaft seal and to be filled.

RBob.

 

Does anyone know where to find a complete electrical schematic for the cooling fan circuit of a '92 firebird 3.1L v6. Also what is the quickest way to check to make sure the fan is good? If I had a schematic it would cure a lot of issues.

 

cant help with he diagram, but if you unplug the fan and just the leads out to a 9v battery, the fan should spin if its good. You can also turn onthe AC and again the fan should turn on

 

Amazing what can be accomplished with a starting point! Knowing how to check the fan should get me headed in the right dir. Your suggestion answered me right on. I think I found everything else I needed @ A.Z. online. Can I reconfig the heater output from the bloc with another type of manifold and be ok. The original adapter from the bloc to heater/throttle body manifold crystallized.