having a problem with the cooling fans not kicking on in the girlfriend’s 1995 Chevy Lumina sedan. they do not turn on even when the HVAC knob is turned to A/C or Max (the A/C doesn’t work anyways, not sure if that matters). the gauge will stay in the middle during highway driving, but will start to creep up during city driving and occasional idling.
i read on some GM forum that if you unplug the ECT (engine coolant temp) sensor while the engine is running, the PCM freaks out and reverts to an emergency mode, turns both fans on, and throws a service engine light. i did do this on her car, and both fans turned on within 1 second, and it threw the light. this tells me that they do have power and ground and are in working condition. i guess i can also rule out the ECT sensor being bad.
replaced both cooling fan relays (passenger side fuse box under hood, #16 and #17).
drove the car around a bit today and it wasn’t really hot enough out to warrant overheating, but the car was idling in the driveway yesterday and the gauge got to 3/4, and slightly past.
not sure what else it could be–any ideas? i’m sure other GM cars from this era are similar in cooling design.
---------- Post added at 04:36 PM ---------- Previous post was at 04:23 PM ----------
was reading on some other GM forums, and people are saying that the car is supposed to get to the 3/4 mark and even farther before the fans even turn on–approx 227F head temp. seems high to be safe–i should mention that technically the car has never overheated (gone into red), so i’m not sure if this is a problem to fix, or if it’s just the way the system is designed.
The sensor may have power and ground however that doesn’t always mean that it is a good sensor. The engine coolant temperature sensor sends a voltage reference signal to the engine control module. If the voltage reference signal is too low, the ECM will not turn the cooling fans on. When you unplugged the ECT, you caused the voltage reference to read zero. This will cause the ECM to turn the fans on as a fail safe to protect the engine from overheating. You can check the voltage reference signal by running a live data stream through a scan tool or measuring the voltage through a digital volt ohm meter. When the engine is cold the voltage reference will be lower. When it gets to operating temperature, the voltage reference signal will be higher. If I remember, I can look up the spec tomorrow for the fan to engage at which signal. I will post my findings. Good luck to you.
My gf has a 97 lumina and it runs the exact same way. 2 electric fans that kick on around 230F. Needle is about 2/3, car never actually overheats. I used to think it was a problem, then one day I just let it run sitting in the driveway till it got hot enough that they came on. Gauge is at 1/3 on the highway so I always thought it was running too hot at idle and that they weren’t coming on. Car just needs to get that hot though before they actually do, I wouldn’t let the gauge scare you.
I would do what I did though just to make sure they kick on on their own.