Radiator Fan Not Working

[Joel Hauser]

My radiator fan never comes on. I let it idle for about 15 minutes. My dash temperature gauge has gone up to close to 220 degrees, but the fan still did not come on.

1. The fan works. It is a two speed fan. I have hooked it up to a separate 12 volt battery and it spins on both the high and low speed circuits.
2. I have replaced the engine coolant temp (ECT) sensor (several times) and it doesnt make a difference. I have a separate sensor for the gauge, which is in one of the radiator hoses. This one is not supposed to go to the EEC. My gauge is working properly.
3. The Electronic Engine Control (EEC) aka Engine Control Unit ECU aka PCM is new and good. The engine is running fine (for a change).
4. The constant control relay module (CCRM) is a pretty new used replacement. It is not rusty. I tapped it with a hammer - light taps - and that didn't help.
5. I checked the 60 amp fuse and it looks good to me. There is continuity across the spikes. I have substituted another 60 amp fuse and a 30 amp fuse, and it still doesn't work.
6. I have checked continuity between the fan and CCRM and it is good
7. I have checked continuity between the ECT sensor and the EEC and it is good.
8 .I have checked voltage at the CCRM and I have voltage there “all the time” on the pins that are supposed to have voltage.
9. I have checked continuity between the CCRM and the EEC and it is good.
10. I have checked grounds at both the CCRM and the fan ground, and it is good.
11. I have put a jumper wire across the two ECT sensor plug terminals , and that did not turn on the fan.
12. I have checked continuity from the 60 amp fuse to the CCRM and it’s good.

My thought is the CCRM has a bad fan relay, although I've read these almost never go bad. The CCRM has 3 or 4 relays in it. One for AC (which I don’t have); one for the fuel pump (which is working), one for low speed fan and one one for high speed fan. I don't believe the CCRM is serviceable. You replace them when they go bad. They are not cheap.

I intend to install an additional manual fan switch at some point, but I don’t think I can do that until I get the existing circuits working properly.

Are there any other diagnostic tests that I should be looking at before I throw more money at a CCRM?

I read one post on another forum: “Stock tune in 96s and 97s turns the low speed fan on at 208 degrees and off at 200 degrees. It turns the high speed fan on at 228 degrees and off at 224 degrees. The 98 tune is probably the same, but I don't have that for my PRP. These engines like to run hot.” https://www.corral.net/threads/96-98-cobra-cooling-temp-questions.1147311/

That seems awfully hot to me. But I would have thought that putting the jumper wire across the sensor plug terminals would have over ridden the sensor and turned on the fan, no matter what the coolant temperature is

this is a 1996 4.6L SOHC motor, donor radiator and fan.

Thanks everyone.

Joel

[weendoggy]

Within the CCRM, both hi/low fan relays get power from the CJB and BJB for controlled and full-time power. Within that is the microprocessor that delivers the ground side to activate (via PCM) the low speed fan. The high speed is controlled via PCM ground. Both are controlled via PCM/ECT info. You'll need to look at the CCRM schematic in order to see how it works and much easier than explaining. If you want the PCM to control the fan, you will need to fix this issue. This means checking pin connections/locations at both PCM and CCRM. The ECT sends a VREF signal through it back to the PCM. It should be easy to check the high speed relay by grounding the output to ground (instead of the PCM) and that should tell you if the high relay is working. Or, you can easily install a thermo fan switch in the system and route that through a relay to the fan and also wire your toggle (override) to activate it. This would be separate from the PCM and CCRM.