TrailRiderRob
New Member
Hi folks,
Hopefully someone has had this problem and been able to solve it. Sorry, this is a bit long, but I have spent a lot of time troubleshooting this and want to make sure I cover everything I have done so any real car gurus can help think of something I am missing.
The problem is the engine cooling fan on my 02 Liberty sport 3.7L will not come on at 203 DegF (this is what the manual says) like it should . It will not come on at 204 205 206 or at any time up to the 220 DegF that I am willing to wait for the PCM to turn it on before I shut the engine off.
The engine cooling fan DOES come on when I turn on the AC (or turn on defrost) so this tells me that the entire circuit from the pcm to the fan motor is good. In the wiring diagrams the signal to turn on the fan (regardless of why) comes from the pcm to the engine fan control module/relay telling the module to supply power to the fan.
Pause for a little history on the vehicle. I bought it not running for $500 hoping that I could put reman heads on it and drive off into the sunset, but it was to late and one valve seat fell out and ruined cylinder 2 piston. Not being a quitter, I bought a remanufactured engine from a reputable retailer. So it has a better than new engine with new water pump, new thermostat. Of the cooling system the only parts from the original are the engine coolant temp sensor, radiator, the heater core and the hoses.
I thought, "bad engine coolant temp (ect) sensor" and tested it using a multimeter. It tested out good, but I later replaced it anyway.
I hooked up my OBD scanner which can monitor the coolant temp in near real time (so I can watch it climb steadily to 220) and this tells me that the pcm IS receiving the signal from the ect sensor (since the data on the OBD port is coming from the pcm). I also unplugged the connector from the ect sensor while the engine was running which instantly killed my temp reading on the scanner (and temp gauge on dash) both readings returned when I plugged it back in. I also unplugged the fan control module and ran a quick scan using the OBD scanner. It gave the OEM code P1491 (Radiator Fan Control Relay Circuit) as it should. After plugging the module back in it did not give the code again.
The only thing that I can conclude is that this is a problem inside the pcm, either software or hardware.
One last strange thing, as the engine warms up with my OBD scanner connected I closely watched the temp gauge on the jeep and it climbed in line with the temp displaying on the scanner, until around 195DegF, then the temp gauge would not go any higher (just below midpoint), even though I could watch the temp continue to climb using the scanner.
There are a couple of other problems I am working on that are probably affecting how hot it runs, but should not prevent the fan from coming on. The Catalytic converter on the side that dropped the valve seat was ruined. I ordered a new one, which didn't come yet, so I am using the old one (after punching several holes through the melted honeycomb) so the exhaust gases can still flow. The old radiator was pretty rusty inside and even though I flushed it while I had it removed until the water came out clean and flushed the heater core while the engine was out and then back flushed the entire system again after it was all together. Then I drained the cooling system and filled it with 50/50 mix of the Mopar HAOT coolant and distilled water then bled the air out using the bleeder near the upper radiator hose. I am still getting some rust back into my coolant reservoir during testing, so I broke down and ordered a new radiator. Last symptom is that the heater is blowing "lukewarm", but not hot air.
Plans today are to pull the thermostat out and test it then wait for the new radiator. Still, my fan should come on.
Happy trails and Thanks for any help.
Hopefully someone has had this problem and been able to solve it. Sorry, this is a bit long, but I have spent a lot of time troubleshooting this and want to make sure I cover everything I have done so any real car gurus can help think of something I am missing.
The problem is the engine cooling fan on my 02 Liberty sport 3.7L will not come on at 203 DegF (this is what the manual says) like it should . It will not come on at 204 205 206 or at any time up to the 220 DegF that I am willing to wait for the PCM to turn it on before I shut the engine off.
The engine cooling fan DOES come on when I turn on the AC (or turn on defrost) so this tells me that the entire circuit from the pcm to the fan motor is good. In the wiring diagrams the signal to turn on the fan (regardless of why) comes from the pcm to the engine fan control module/relay telling the module to supply power to the fan.
Pause for a little history on the vehicle. I bought it not running for $500 hoping that I could put reman heads on it and drive off into the sunset, but it was to late and one valve seat fell out and ruined cylinder 2 piston. Not being a quitter, I bought a remanufactured engine from a reputable retailer. So it has a better than new engine with new water pump, new thermostat. Of the cooling system the only parts from the original are the engine coolant temp sensor, radiator, the heater core and the hoses.
I thought, "bad engine coolant temp (ect) sensor" and tested it using a multimeter. It tested out good, but I later replaced it anyway.
I hooked up my OBD scanner which can monitor the coolant temp in near real time (so I can watch it climb steadily to 220) and this tells me that the pcm IS receiving the signal from the ect sensor (since the data on the OBD port is coming from the pcm). I also unplugged the connector from the ect sensor while the engine was running which instantly killed my temp reading on the scanner (and temp gauge on dash) both readings returned when I plugged it back in. I also unplugged the fan control module and ran a quick scan using the OBD scanner. It gave the OEM code P1491 (Radiator Fan Control Relay Circuit) as it should. After plugging the module back in it did not give the code again.
The only thing that I can conclude is that this is a problem inside the pcm, either software or hardware.
One last strange thing, as the engine warms up with my OBD scanner connected I closely watched the temp gauge on the jeep and it climbed in line with the temp displaying on the scanner, until around 195DegF, then the temp gauge would not go any higher (just below midpoint), even though I could watch the temp continue to climb using the scanner.
There are a couple of other problems I am working on that are probably affecting how hot it runs, but should not prevent the fan from coming on. The Catalytic converter on the side that dropped the valve seat was ruined. I ordered a new one, which didn't come yet, so I am using the old one (after punching several holes through the melted honeycomb) so the exhaust gases can still flow. The old radiator was pretty rusty inside and even though I flushed it while I had it removed until the water came out clean and flushed the heater core while the engine was out and then back flushed the entire system again after it was all together. Then I drained the cooling system and filled it with 50/50 mix of the Mopar HAOT coolant and distilled water then bled the air out using the bleeder near the upper radiator hose. I am still getting some rust back into my coolant reservoir during testing, so I broke down and ordered a new radiator. Last symptom is that the heater is blowing "lukewarm", but not hot air.
Plans today are to pull the thermostat out and test it then wait for the new radiator. Still, my fan should come on.
Happy trails and Thanks for any help.
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