First of all, I screwed up, ... Again! Fuse 19, a 40 amp, feeds the contacts of BOTH relays and fuse 9, a 10 amp, feeds the coil of both relays. More on those circuits in a minute.
One fast thing to try is with the engine running, unplug the two-wire coolant temperature sensor near the thermostat housing. That will set a fault code and turn on the Check Engine light, but it should also cause the fan to turn on. If it does, you'll know the computer is working and has control of the relay. If it does not turn on, the best approach is to find a scanner that can turn the relays on and off to see if the computer responds.
Another way to test the switched part of the relay circuit is to ground terminal 86 of the low speed relay. This is different numbering than I'm used to seeing, and there have been so many mistakes in the service manuals that it's better to describe how to find that terminal. Pull the relay out and measure the voltage on the four terminals. Two of them should have 12 volts with the ignition switch in the "run" position. If you can sneak your voltmeter or test light probe under the relay when it is reinstalled, and can get the voltage readings on the two remaining terminals, one of them should now also have 12 volts. That's the one to ground. Touch a grounded wire or use a paper clip as a probe to touch that terminal. That should make the relay click on and the fan should run. That will prove which part of the circuit has the problem.
I apologize that I have to leave for a couple of hours, but I'll check back as soon as I get back.
Sunday, June 5th, 2011 AT 11:56 PM
