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I have a 1994 Bonneville SSE and recently noticed the cooling fans are always 'on' - both of them, all the time. AC is off or on, doesn't matter. They come on when the ignition is turned on and the car is cold.

I pulled the relay / fuse cover on the firewall, but the relays are not labeled. Any help on how diagnose / troubleshoot would be appreciated.

the layout of the relays looks like this below;

(Passenger side) [relay] [relay] [empty] [empty] [relay] [relay] [relay] [relay] (drivers side)

does anyone know which relay(s) control the cooling fans? I thought possibly one or more of the relays are stuck; the car has been sitting for 6+ months in storage.

Thanks in advance for the help!

The relays are all the same, I believe. Swap them around and see how behavior changes.

The two relays on the right (driver's side) control the fans. I swapped them out with the AC and Horn relay and the fans still come on. Engine is cold, AC is off.

I suspect a sensor, but not sure where to look. The car is new to me, so i'm still learning it. Any advice on where to look for the problem is appreciated.

thanks!

There are two engine coolant temp sensors, one for the pcm and one for the gauge on the dash. There may be a problem with the pcm one or its wiring. I don't know where exactly they are on a L27, or which is for what. You could also try running a temporary ground to the relay ground pin and see if that helps. I forget if ground on or off turns the fans on, but if you have a bad ground to the relay, it wouldn't do it's job.

The PCM will set fans on if it believes there is a temperature sensor issue. This can be confirmed with a code scan (sets code) and reading live data.

Coolant temperature sensor is in the side of the block, in line with the throttle body. You likely have to look from the driver's side to be able to see it. It's buried pretty deep.

From what I recall, it's a 3 wire sensor. 1 common, 1 lead to the PCM, and 1 lead to the temperature gauge (if so equipped).

Here are the two coolant sensors on a L27 block. The black two wire one is for computer and the white one wire one is for the gauge.

Thanks for everyone's help on this. I will let you know how it turns out.

Someone suggested it might also be the AC pressure switch (faulty)... signaling the PCM to turn on the fans.

A live data scan will tell you if the PCM wants the fans on or not, and why, if you read between the lines. If it thinks the engine temp is high or that the AC needs it.

Wikoff - thanks for the info. Can you recommend a tool or software to do the data scan?

I have an ODB II code reader (Harbor Freight). This car is new to me, so I'm learning as I go here.

Thanks again for the help.

I've never had to use one on a hybrid OBD 1/2 pcm, so I don't know one off the top of my head. Not all code scanners will do live data, so pay attention to what you're getting. Local parts stores may have a loaner unit.

I use an actron CP9145 for this. Usually the scanners that can get these cars do both OBD 1 and 2. Just confirm they are specifically compatible with the 94/95 Bonneville before buying.

I tried a CenTech ODB II scanner and it would not recognize my 94 SSE. The port connector is ODB II though in the car.

I will check out the one you recommended. For the cost, I may just take it to a shop at this point.

Thanks - Jim

The old CP9110 Actron works for the 94/95s with the correct cable and cartridge. There's a few on ebay right now but I don't see the correct cable.

If you get your own OBDII cable, you can splice it in to whatever cable the Actron comes with using the following diagram:

95naSTA - thanks for the diagram and info. I may get an Actron off ebay or just take it to my dealer buddy.

I ran the AC this morning on the way to work, shut it off (pressed OFF on dash) and miraculously the fans stopped running as I parked. Makes no sense to me. We'll see if the problem resurfaces.

Thanks again and to everyone for their help on this.