Coolant fans will not run

Asked by May 24, 2011 at 08:13 PM about the 1994 Pontiac Grand Prix 4 Dr SE Sedan

Question type: Maintenance & Repair

I have a 3.1L with 170000 miles. I recently replaced the intake manifold and upper plenum gaskets along with thermostat.  While bleading the air from the system the car became very warm, almost redline before shutting it down.  The fans never came on.  I have checked the fans, they run fine. I have checked both the primary and secondary relays, thay work as well.  Checked for power at the relay both the power side and coil side have power at the relays.  One latch side is hot in run and the other is hot all of the time. I checked the control voltage at the temp sensor plug it is at 5 volts.  I have checked the resistance acorss the sensor it is 3000 ohms at 80 degrees and in the 200 ohm range when the termostat opens.  When I start the car and unplug the temp sensor connector to create an open loop situation both fan come on. They will not come on with the A/C on max with the blower on high either. Is there a way that I can verify if the ECM is latching the fan relay closed or maybe something I have overlooked?

2 Answers

125

as a certified technisian the only way to test the ecm to make sure its doing is to plug it into a scan tool and look at the display screen of whats all running and testing setup on the scan tool and maybe manually turn on the fans and if that works the ecm is definitely in need of replacement. but be carefull and make sure to wear the ground strap they give you to install it with. ive installed a ecm in my wifes 97 and fried the first one without wearing the strap they provided me with. wont do that again. and the 3.1 is a good engine. just take care of her and shell take care of you. thats all i got hopefully it helps. you might have to go to a shop and have then do that. which is about 80 to 100$ depending on the shop. so good luck

1 out of 1 people think this is helpful.

Just replaced water pump on 94 Gran Prix and not the one fan closer to water pump won't come on

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