North American Turbocoupe Organization

Cooling Fan Test
andrewjs18 Offline
Checking the Engine Cooling Fan Operation
by Jeff Korn and Pete Dunham

OK, here is the low down on the fan system on the 87-88 TC. Both fans are controlled by the EEC via the IRCM (Integrated Relay Control Module), which is the black box with about 24 wires coming out of it located on the front of the passenger's side strut tower. To test the aux fan (the smaller drivers side fan) pull the connector off the A/C pressure switch, which is in the high side A/C line near the VAM. Turn the key on, and jumper the 2 pins in the connector you just removed. If the aux fan runs, its relay in the IRCM is OK.

There is an easy way to check the operation of the main (pass side) fan. Run the KOEO EEC diagnostic test. During the test, the main fan should run. If it does, the IRCM, and all the main fan wiring is functioning correctly all the way from the main fan to the EEC. If the main fan comes on during the KOEO test, but fails to come on when the motor gets hot (stock temp gauge up about 1/2 way), the most likely cause is a bad ECT. If you still suspect the IRCM is faulty because the fans failed the above test, then do this before replacing the IRCM: be sure the heavy yellow wires going to pins 3 and 4 of the IRCM are hot at all times. These wires provide power to the fans directly from the battery thru fuse links "L" and "M". Test this with a test light, not a voltmeter.

Running a code test may show a bad ECT, but only if its temp readings are WAY out of wack. In other words, the ECT may be reading temp as lower than it really is, but still not set a code.

There is one relay for each fan in the Integrated Relay Control Module (IRCM) which is the big black box on the front of the passenger side strut tower. Also in there are the power relay for the engine control computer, the fuel pump relay and one other. At least one of our members has replaced relays rather than buy a new/rebuilt IRCM. From his verbal description it takes some electrical finesse. but I can't tell you more. I'll send him an e-mail and see if he will post something on it.

Here is some info for testing the relay for the driver's side fan.

Here is how to check the relay for the drivers side fan (smaller one) in the IRCM: Find the PINK wire at terminal 17 of the ICRM. Probe it with a pin, like when checking the TPS voltage. Run a jumper from the probe pin to ground with the key on. When the pink wire is grounded, the lower, drivers side fan should run. If the fan runs, the IRCM is OK. I have tapped into this pink wire, and use a relay to ground this wire whenever the HVAC function lever calls for A/C, so I have both fans running when the A/C is on. Motor stays nice and cool this way, and my 130A alt easily handles the load.

To test the other relay, do the above to the tan wire w/ orange stripe, it goes into the 2nd from the bottom position on the I/C side of the connector. Not 100% on that but I did this recently and I think that's the one.

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