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GM Tech (Cam)
GM Tech (Cam), Pontiac Technician
Category: Pontiac
Satisfied Customers: 2377
Experience:  GM Grand Master Technician 2007. 14 years experience.
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Here is my problem child. 06' Pontiac Vibe 1.8L vin 8.

Customer Question

here is my problem child. 06' Pontiac Vibe 1.8L vin 8. Cooling fan runs on high speed when a/c or non a/c defrost mode is selected. I'm an ASE certified mechanic of 20+ years and this has me going insane. According to Mitchell pro demand. The pcm supplies a ground to relay 1 (low speed) when a/c or defrost mode is requested. As long as certain criteria's are met. A/c request, engine temp below 181 degrees, a/c pressure below 178psi. Pcm commands relay 2 ( high speed) if temp above 199 degrees or a/c pressure above 220 psi. But this vehicle runs high speed fans whenever a/c, defrost mode is selected. Our scan tool offers limited data. Have put gauges on a/c too watch pressures. All within limits. This system involves pressure sensor, resistor, and pcm control. When defrost or a/c is requested turns on high speed. Now the a/c pressure sensor is new, the pcm is new. Same results. All wires from pcm to relay center ohm out good, .8 or less. I know this and the Matrix share same electronics. Havent been able to solve this problem. Theoretically I've cut the relay 2 control to test if the pcm does what I've read. And yes it does. Low speed fan when a/c,defrost requested. Probably not the best test but going by info I have . All powers, grounds are good and clean. I'm almost too the point I think this is normal operation, but according to Mitchell this is not how its supposed to perform. Ideas???
Submitted: 1 year ago.
Category: Pontiac
Expert:  George H. replied 1 year ago.

Hello I will help,

I don't know if I can get to the bottom of this but I do need further data to get to an understanding of what is happening.

What are the pressures you see on the scantool vs the pressure you see on the gauge?

Same for the ECT?

Most systems run the fans on high speeds until the last few years when they dialed them back to save on gas.

Let me know and I will help you as I can.