Hello all,

New member here.

Just bought the truck and have been fixing numerous problems. Coolant leak. Replaced radiator, water pump and timing gears (since I was there). It runs well with no leaks but I cannot get the radiator fan to come on.

I can jumper the relay and the fan runs.

I have replaced the relay and checked the fuses.

I can measure voltage across the coil. I have 12V on the hot side both across the coil and direct to ground. If I connect a test light the light will not light and the voltage drops to zero.

Without the relay installed I do get a P1491. Which I should.

I suspect a bad connection from the PDC to the PCM or the PCM is shot. I'm out of ideas. And I have no way to test that cable connection.

Is this a common failure on the PCM?

Any ideas?

 

temp sender in intake manifold. Won't come on til temp about 210*, OR A/C is commanded on. (and compressor clutch actually engages)

 

Update..

Thank you for the response. I did all the checking with the AC on. Compressor engaged and AC commanded. It's cold in Chicago so I doubt I could get the engine hot....lol. Either way the fan should run with the AC on and compressor running.

I checked the harnass up to the pcm. If I short C2 Pin 17 to ground key-on-engine-off the relay/fan engage. I also checked the 2 grounds to the PCM It must be the PCM. New one on the way.

 

Yeah Chicago sucks. Kankakee here

 

My e-fan wasn't working for many many years and probably well over 100K before I replaced it about 3 months ago. The 4.7 survived on clutch fan alone and it's likely that yours has too. I only found out when exploring conversion to an e-fan and deleting the clutch fan. End result...I replaced the e-fan and kept the clutch... so stock setup. When I installed the new e-fan and it kicked on I was like "well that's a new sound"....LOL

I would say unplug the pigtail underneath and check the voltage at the two pins with AC running. However, you did say it runs when you jump the relay, so you're likely right about the PCM.

 

Do you have an fan clutch and an electric fan too? I have run across either a bad ground or the fan itself. If you have a power probe you can test the electric fan with it to see if the fan is any good. If the fan is good, then trace back to the PDC for either shorted or open wire.

 

Update.

If I short the relay control wire at the PCM connection KOEO the relay turns on and the fan runs. So my thinking is a bad PCM...Wrong. Installed a new PCM and the fan still will not kick on from the PCM.

Im stumped. There must be another sensor telling the PCM not to turn on the fan.

Maybe Ill try putting the engine temp sensor in boiling water to see if that will do it.

Any ideas?

 

According to the wiring diagrams I found, the ONLY sensor that plays a role is the engine coolant temp sensor....... Now, there may be a programming thing inhibiting it as well, but, if engine is at operating temp, or above... and the a/c compressor is running, one would think that the fan should be running as well. However, if your 'Rango has an ambient temp sensor, it may be disabled below some threshold.

 

Earlier years had a temp sensor in the expansion valve that turns off the AC when the evaporator is below 37. The later years may have something similar. Looks like a black box bolted to the side of the expansion valve. It has a probe that goes into the valve block.

 

I don't have an ambient sensor. And according to the wiring diagram i should not. I will take a look at the expansion valve sensor.