If this entails having to put a new radiator in I have a question about the existing radiator. The little black plug on the upper right hand side of the radiator. It's threaded. Is there a thermo switch that fits into that hole ? I would also have to wire that switch which I have no idea about . Bummer

 

when I bought a replacement radiator for one of our bricks's, it had the switch but the car didn't use it, so I just left the switch in place as a plug. that might have been the 1987 240 ? it didn't have an electric fan at all.

ok, well, the fan should have run! so either your relay is bad, or the fan motor is bad.

the wiring diagram shows an inline fuse between the battery and the fan relay. unplug the fan relay, and see if connector A, the red wire, has juice (use a test LED or a volt meter, with the black lead on a chassis ground.

if you do have juice at 1A(red), then jumper 1A(red) to 1C(green) and the fan should come on low. jumper 1A(red) to 2C(red) and the fan should come on high. if that works, then your relay is probably bad. if 1A has power and jumpering it to 1C/2C doesn't work, then the fan motor is probably bad.

 

Went ahead and replaced the relay . Fan still wont turn on . Looks like I'll be replacing the fan next . If that doesn't do the trick I don't know what the problem is.

 

Did you test the fan directly?
Your car must have been modified at some point... But it seems like it was awhile ago which begs the question how did the car run and not overheat all this time?
I still think that there has to be wiring somewhere that went to the switch. The wiring should be somewhere in the wiring pack under the battery or thereabouts.
How is your cooling system apart from the fan not turning on?
Is the radiator circulating well? Is it uniformly warm across?

 

did you run my last test? that would have identified if the fan motor was functional by manually applying power to both the low speed and high speed sides of the fan via the relay socket...

again, for emphasis...

the wiring diagram shows an inline fuse between the battery and the fan relay. unplug the fan relay, and see if connector A, the red wire, has juice (use a test LED or a volt meter, with the black lead on a chassis ground.

if you do have juice at 1A(red), then jumper 1A(red) to 1C(green) and the fan should come on low. jumper 1A(red) to 2C(red) and the fan should come on high. if that works, then your relay is probably bad. if 1A has power and jumpering it to 1C/2C doesn't work, then the fan motor is probably bad.

 

Pierce, I ran the test. The fan comes on high and low. The relay is brand new yet the fan still will not work . What else could it be ? A bad fuse ?

 

What does the inline fuse do and where is it ? Could that be the problem? I running out of ideas

 

if the fan comes on at all, then the fuse is good. if the fan comes on doing the DTM3 test with the onboard diagnostics, then the fuse, relay, and ECU control system are all working.

if thats all good, and the fan still doesn't come on when the engine gets hot, I suspect its the engine coolant temperature sensor (NOT the same sensor for the dashboard gauge, the ECU and ICU use a different 2-wire sensor).

 

I already replaced that sensor. We bypassed everything we could think of. Everything worked independently. When we put the plugs back into the relay the fan won't turn on when idling. Could it be a wiring issue?

 

but the fan works in the DTM#3 test at low and high speed?

mine (1992 745T) doesn't come on at an idle unless its pretty warm out, there's no breeze, and I leave it idling for 10-15 minutes while dinking around with stuff.

 

Hi Pierce,
No the fan doesn't come on either hi or low during the DTM#3 test . Makes me think there's a wiring problem somewhere.

 

back there a ways, you said the fan does come on? doing what, exactly? doing the jumper 1A to 1C or 1A to 2C tests at the fan relay socket ? if those work, that means you have power at 1A which means the fuse is good. and it means your fan motor is good, as is the wiring from the relay socket to the fan motor.

I believe you also said you heard the relay clicking during the fan portion of the DTM3 test ? DTM3 also tests a bunch of other stuff in sequence, including the idle air controller, and the injectors, so don't confuse those.

 

The fan comes on when jumping the 1A B C tests. Everything worked liked it should have when jumping and only when jumping.

The fan will not come on during the DTM3 .

 

ahh, ok. so that tells us the fan itself and fuse are good, but the relay is suspect.

I dunno if you can readily access the back of the relay socket with the relay plugged in... but if you can, take a jumper wire clipped to ground, and touch it to the back of connector 1B (low speed) and 2B (high speed) (car doesn't have to be switched on). if the motor runs, then the relay is good too.

 

Hi Pierce ,
We tried that as well . The fan worked fine on both low / high speed . Any other suggestions ?

What we have so far :

1) The fan doesn't turn on during the DTM#3 test
2) The fan doesn't turn on while idling .
3) Fan works during all the jump / bypass tests
4) Fan works when a/c is running and when defrost is running
5) Replaced : fan relay , thermostat , and the temp control sensor(the one in back , not the one for the temp gauge) .

 

well, if grounding relay pins 1B and 2B ran the fan then the relay is good.

hmm. remove the passenger side foot well liner, remove the passenger side right fender liner (just forward of the right/passenger door)... behind that panel should be the ECU. car switched off, unplug the ECU connector, and if you look in the connector plug, you should see the pin numbers with a small flashlight. carefully use a jumper wire to ground pin 10 or 11, and the fan should run in high or low speed... ECU pin 10 is connected to the relay pin 1B, and 11 is connected to the relay pin 2B.

if THAT works, then I have no idea why the DTM3 isn't running the fan, as it sure should be. bad wiring somewhere between the ECU and fan relay?