jlaucks

Hi guys,

I have to say I have exhausted almost every post on this forum to try to solve my 2004 Jeep Grand Cherokee Laredo 4.0. But I need a little more help

A quick back story: The jeep started to overheat in traffic with the A/C running, check gauges came on, Temp gauge was way beyond the comfortable zone and it started to overheat and push out coolant out of the overflow. Got a tow back home and got down to business. After a lot of research I tried replacing the fan relay. Turns out the 2004 has fan relays in the fuse box under the hood.

Here is where the trouble starts. When you go to the auto parts store they try to give you the older style relay. This is what the previous owner had installed. He has the power from it jumping back into the fuse box. Long story short it was a hack job. He tapped a new pin into the C2 connector on the ECM, stole power from the fused hot and then had the control jumping back into the High Speed fan relay to try to power the fan.

I started to try to repair the bad wiring and though maybe it make sense to put it back to the stock relay set-up. I got the new block style relays for in the fuse box, replaced the fan motor with the correct 3-wire motor (previous owner had the 2 wire spliced in) but the fan still will not turn on either by switching on the A/C or once it gets up to temp.

I did manage to power the fans by putting a jumper across both the high and low speed relay slot so I know that the circuit between the fuse box and fan is good. This told me that something is causing the ECM not to tell the relays to turn on the fan. I have voltage & ground at the Temp. Sensor on the thermostat housing and I also replaced that sensor for good measure but still no luck.

I am thinking that the issue still lies in the wiring between the Fuse box and the ECM but I am hesitant to dive into it with out a good wiring diagram. It seems like things are different on the 2004’s in the fan relay area and it is not covered in the FSM’s that I have.

Have any of you gotten into the wiring between the PCM & the ECM? Any help would be certainly appreciated!

Thanks,
Jared & the sad/hot WJ

dave1123

If it were my jeep, I'd just go with an aftermarket fan controller completely separate from the jeep's system and be done with it. If you private message Bustedback, I'm pretty sure he'd tell you which system he is using on his ZJ. He has mentioned it on some of the posts about the problem of mounting and controlling an electric fan to replace the clutch drive units.

That's just my opinion.

jlaucks

Thank you to everyone on this thread for your help and suggestions.

This one was a long battle. Ended up replacing the temp sensor and repairing a lot of wiring in the process.

Short of it is that the wires going from the '04 relay slots in the fuse box to the ECM were not matching the correct pins on the ECM as shown on an '04 wiring diagram. I ended up re-installing the old style fan relay and the CEL & issues have gone away. Just made sure to wire it in well this time with good connection & heat shrink rather than twisting wires and taping them.

I also picked up a mechanical fan 'upgrade' incase the relay ever decides to give out on me again.

-J