Why are the radiator fans not turning on?

MRTKSAMO

MEMBER
2010 JEEP LIBERTY
3.7L
V6
4WD
AUTOMATIC
150,000 MILES

A car came into the shop and had a charging problem. It took me no more than 10 minutes to diagnose the issue and being the voltage regulator in the PCM went bad. Replaced PCM and started the car for the first time in 2 weeks and let it idle to charge the battery. The car overheats while idling. From quick inspection the customer has replaced the radiator and the fan. The reason the vehicle is overheating is because the fans aren’t coming on. Checked radiator fan circuits relays fuses and all. All seem to be working properly. I have ground I have power and pretty sure I have signal. I can only turn the fans on either from my scan tool or by jumping the relay on the fan control. I’m losing my mind checking things. Could a faulty temperature sensor read the correct temperature but not trigger? The PCM to turn the fans on? Could I have bought a faulty PCM that the only thing wrong with it is the fan control? Could I jump the temperature sensor connector together to check if the fans go on that way it’s a bad sensor. I’m lost I’m almost about to wire up a separate unit with a circuit breaker and have it gone off a generic temperature sensor and have the system separate from the PCM. Another question is in the Liberties PCM is it providing ground to close the circuit thus turning the fans I need a diagram please for the radiator fan circuit and for the PCM. I have a couple of TIPMs laying around I tried swapping them out and all the relays. The only sign I had of bad wiring was major corrosion on the fan relay the one next to the headlight. I cleaned up the wire checked for power and ground and put a relay in and nothing still.

7 Replies

BORIS K

MECHANIC
795 POSTS

Hello,

Please see wiring diagram below.
The TIPM is responsible for outputting the fan relay coil signal brown/light wire from C3 pin 2 to the external high speed fan relay.
The low-speed fan relay is mounted on the TIPM and is also triggered by the TIPM.
The TIPM will receive the fan relay on command from the PCM via CAN C.

Hope this helps.

Cheers, Boris

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Thursday, August 18th, 2022 AT 12:39 AM

MRTKSAMO

MEMBER
3 POSTS
2010 JEEP LIBERTY
3.7L
V6
4WD
AUTOMATIC
150,000 MILES

2010 jeep liberty came into the shop with a charging problem. After a strict diagnosis it was determined the voltage regulator was bad in the pcm. Car sat for 2 weeks waiting for pcm put it in and programmed all is well Untill we left the car idling to charge the battery. Car over heated further diag pointed out the fans were not kicking on. They can only be turned on by my scan tool or by jumping the relay. I have checked everything I can think off fuses relays. The o to sign I had and hope was with the fan relay located on the side of the rad support had major corrosion cleaned the connector checked for power ground put a new relay in not the same one but should do the job and nothing. Coolant temp sensor reads because when it over heated it was in the red. Can a faulty temp sensor still read temp and not send signal to pcm? Does anyone have a diag of the pcm and or radiator fan control circuit I can use? All data seems to be down at my shop.

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Thursday, August 18th, 2022 AT 12:37 PM (Merged)

KEN L

MASTER CERTIFIED MECHANIC
47,536 POSTS

It sounds like the TIPM is out which is common. Are here any trouble codes? When the TIPM goes out it may not have codes here is how the fan control works in the images below and I have included how to change out the TIPM which is easy because itself learns. Check out the diagrams (below). Let us know what happens and please upload pictures or videos of the problem.

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Thursday, August 18th, 2022 AT 12:37 PM (Merged)

MRTKSAMO

MEMBER
3 POSTS

Thanks for all the help guys seriously. So, I had a TIPM on hand swapped it out and still the same. I don’t know if I had mentioned but the computer was replaced because the vehicle was not charging the regulator had gone out. The car came in on a flat bed and had noticed it had a new radiator and thermostat connector looked new so an overheating problem was there prior I just can not trouble shoot it with the old PCM because the vehicle would not stay running. At this point I am thinking there is a bad wire going from the TIPM to the PCM I will use these diagrams to further trouble shoot u less the PCM we replaced is also defective which I doubt just for the fan circuit to be down.

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Saturday, August 27th, 2022 AT 1:57 PM

KEN L