Just bought this car for my son to go to college with and it overheated yesterday.

Previous owner said he replaced the cooling fan fuse...which should have tipped me off that something else was wrong.

Anyhow, I checked at the cooling fan relay, main power to the relay is good, power to energize the relay coil (via temp switch and ECU) is good (energizes when hot), output of power from energized relay is good but no power at the fan itself (as checked at fan connector.)

I should mention that I've only checked the passenger side fan for operation. It seems to be the larger of the two so I figured it was the "main" fan....????

Jumping the fan leads directly to the battery powers up the fan no problem.

I figure one of two things is happening. Either there was a short in the wiring from the relay to the fans (which blew the fuse for the previous owner) and now there is just no continuity between the relay output and the fan...or 2) there is some other "black box" between the fan relay and the two fans.

Can't seem to find anywhere which of the two fans is supposed to come on first and what controls one vs two fans running. I assume it must be determined by a temperature sensor somewhere. Even if the driver's side fan is supposed to come on first then the passenger side fan...obviously neither one was running when the car overheated.

Anybody know what the sequence of operation is for these two fans and if there is another box/device in the system I need to check?

 

Hello and welcome to the site!! It would help us all out alot if we knew what car we are to help with Please fill out your signature (use mine for example) so we dont always have to ask So what car is it, does it have AC, auto or manual, engine size and any other details that might help.

Can you trace the wiring at all from the relay to the fan or does it disappear into a spaghetti factory of harnesses?

 

Sorry, thought this was posted in just the Protege5 forum. It's a 2002.

A/C, manual, 2.0L (I think.)

Wiring harness disappears into the front end. I didn't want to start ripping off all the harness tape looking for a short.

 

I would just run a fresh wire from the relay to the fan(s) as a temporary solution so it wont overheat again, have you tried turning on the AC to get the fans to come on or at least the relay to energize?

 

The relay will energize via the temperature switch/ECM and output power to the "downstream" side of the relay. That power just doesn't reach the fan(s).

I can rewire it from the relay to the fan directly but I need to know if both fans are supposed to run off this one relay circuit.

I still don't know if both fans are supposed to come on and off together, or whether one comes on first, then the second one kicks in at a higher temperature. If so...I don't know what circuit or device controls that.

 

Is there only one fan relay? Does/Do the fan/s have a box attached to them where the power goes in or is it directly to the motor? One fan is the main cooling fan and the other turns on when the AC is turned on OR when the engine is running too hot. Whats the amp rating of the relay? This pic is of my fan from my 3, it has a control box mounted on it before the fan.

 

There is only one relay labeled "Cooling Fan" in the under the hood fuse box.

The passenger side fan is wired direct to a connection, the driver's side, I'm not so sure, have to check that one.

 

Cheap wiring diagram from a haynes manual should help a ton. Only reason I bought the haynes for my Miata. Just my two cents.