Coolant/radiator fan

NOLE76

MEMBER
NISSAN

I have a '95 Nissan Quest XE, 3.0 litre, 165000 miles. The coolant fan will only run when the A/C is on. I have (following a Haynes manual) checked the sending unit(ok) the relays (ok) the power to relays (ok) the fuses, both in the engine compartment and the passenger compartment (ok). I discovered this when the radiator got so hot that a tank burst, when the vehicle was idling without the A/C running. Surprisingly enough the engine still did not overheat. Do you have any ideas? Iam wondering if it could be the main (PCM) computer, but how could I diagnose that?

By the way, the fan is new - I originally thought that was the problem. Also it is a two-speed fan that is supposed to run on low once the vehicle warms up, and then on high if you pass a certain temperature. I forgot to mention, if I disconnect the temperature sensor, the fan will run on the high speed. It will only run on low when the A/C is turned on, if you turn off the A/C it stops.

2 Replies

2CARPRO JACK

MECHANIC
11,533 POSTS

Check for the "trigger" from the PCM at the relay to turn the fan on. If you jump power across at the relay plug does the fan turn on? Might be a faulty or out of range coolant temp sensor

Was this

answer

helpful?

Yes

No

Thursday, April 12th, 2007 AT 7:45 AM

NOLE76

MEMBER
2 POSTS

Thanks for the response - I checked the resistance of the sensor, and it fell within the required ranges, hot and cold - I then replaced it anyway, grasping at straws, but no luck. If I have the codes pulled do you think I could discover if the PCM itself is faulty?