96 volvo 850 GLT 200k+ miles. Im working on it for a friend. The car overheated and he drove it until it died.
I replaced the motor.
replaced busted radiator and busted coolant hoses.
replaced stuck thermostat.
replaced dead ECT sensor.
Replaced dead and stuck coolant fan

I can ground pin 1 and 2 on the relay and the fan works. high and low
I can unhook the high pressure sensor and the fan kicks on high.

Doing a voltage drop on pin 1 of relay shows 6v, so Im getting a half a ground from ECM all the time.
Doing a voltage drop on pin 2 of relay shows 2-4 volts, Im getting 10V all the time to pin 2.

A/C compressor cycles on and off with no fan activation..same voltage readings.

Did I miss something during the install? Ground maybe? To me, the ECM seems to be also bad..but what else could effect the ground output to the relay? Or am I just reading it right and the relay activates with a 6v ground?

thoughts?

 

No one got anything? Im sure this topic is beat to death due to its awesome fail rate...but I cant get answers anywhere..surely the largest volvo forums can help.

 

Sounds like a bad ECM. For a temporary fix, you could wire the fan to a toggle switch and have the driver manually use it when needed.

 

I thought about a toggle switch. ..but the owner cant be trusted. He knew the car was overheating and continued to drive until it burnt a hole in every piston. Cant trust him with a switch.

I have to fix it right.

With the compressor cycling. ..with no fan...what else can I check? Besides the heater core, ive replaced the entire cooling system...anyone in mid missouri got a spare ecm I can try?

 

Maybe do a search on the forum or look online to see if you can find a wiring diagram for the cooling fans and go from there......I'm thinking it has to be either a bad ground, or a bad ECM.....

 

Service the AC so it stays on. The fan may not kick on for 15 seconds or so.

The fan usually will not come on until the coolant temp reaches 216° and goes back off at 206°… So, you will have to connect an OBD2 gauge to check that.