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Juan Crespo
Juan Crespo, ASE Certified Technician
Category: Pontiac
Satisfied Customers: 1526
Experience:  A.S.E. Master Technician, Advanced Level, Emissions - Asian, Domestic, & European
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05 grand prix n/a. Cooling fans work with ac on and when

Customer Question

05 grand prix n/a. Cooling fans work with ac on and when commanded by scan tool. But when temp gets to the 212 degree Mark which all data says the fans are supposed to turn on they dont turn on and temp climbs. Yet today fans did work as supposed to and cooled off engine at 212. But only once. Then temp climbed back. Where do i start my diagnosis? Ect, relay pcm?
Submitted: 12 months ago.
Category: Pontiac
Expert:  Juan Crespo replied 12 months ago.

Hi there.

Start your diagnosis with a good visual inspection that includes disconnecting and looking closely at all pertinent connections, such as those for the ECT, PCM and fan relay - look for any signs of dirt, corrosion or debris that could cause an intermittent connection.

If no fault is evident, then you'll need to look at coolant flow - the fact that it works properly sometimes makes me think of a possibly faulty thermostat affecting coolant flow and thus ECT signals.

One more thing you could look at is the actual ECT signal - if your scan tool is capable, change ECT PID to volts rather than degrees, then start monitoring it from a cold start to make sure the signal value goes down smoothly. Replace the ECT if any abrupt changes are noticed.

Please let me know if this helps.