QuestionHello, I have a 1992 Dodge Caravan 3.3 Engine with AC. The radiator blew and has been replaced. Found that the coolant fans was not working. The coolant fan wiring has been tampered with previously at fan location and I repaired it, coolant fans still inop I have changed the temperature coolant sensor, fan relay switch, and is still inop. I looked for a bad ground but couldn't find any. I unplugged the temperature sensor, fan started, engine was warm. I plugged it back in and fans still stayed on. The engine then after trying to start, hesitated and stopped retrying it started running with a high idle and then went back to normal idle after that point I noticed the check engine light was on after with engine running. The fans will then stay on continuously still. Dismantled harness looks good, cleaned ground at main harness below Left Hand shock tower. Check continuity from temperature sensor and wire to PCM, it is good. Retrieved codes through ON, OFF instructions, found codes either 45 or 35.
35 code translates open/short at coolant temperature sensor circuit. To recap it is hard to start, check engine light is ON, fan is continuously running whether hot or cold, what are possible diagnosis or solutions. Also why is the check engine light now staying on and how do I clear that code. Thanks for your time.
AnswerHi Brandan,
The code can be cancelled by disconnecting the battery for a few seconds, except that a code 12 will set and it will disappear in a while (50-100 key on-off cycles), but that alone will not cause the check engine light to go on again.
As to your problem with the fan:
I am thinking it is either indeed a short between the engine control module and the relay, or a short in the wires from the coolant temp sensor to the ecm. For example it is normal for the fans to come on when you disconnect the plug from the coolant temp sensor, but they should go off once you reconnect the plug (unless the engine is so warm that the fans are required). So I would suggest that you recheck the wires from the sensor to the ecm: black/light blue is a sensor ground wire that should be attached to pin 4 of the ecm, and the tan/black is the signal wire and goes to pin 2 of the ecm. That latter wire should show continuity and also it should show a high resistance between it and ground. It would be good shake the harness wires for the sensor when you are doing this checking to verify that the readings are solid and not flakey.
As to the fan relay operational wires: When the key is 'on' there should be 12v on the dark blue wire at the relays, and for the low speed relay the dark blue/pink wire should show 12v also for the high speed relay the yellow wire should show 12v, so long as the engine is cool. Now there is also a high speed fan ground relay that is activated by the "radiator fan switch"* which is located at the "front of the vehicle" but I am unclear why that is needed or exactly where the switch is located, but that switch may in fact be closed and that would cause the high speed fan to operate continuously as you described. So it appears that the high speed fan relay can be turned on at will or by decision of the ecm. See if you can find that switch which is connected to the high speed ground relay by a yellow wire. There are two yellow wires at that relay on the same pin, the other one goes to a pin at the high speed fan relay itself that also has two yellow wires.
The relays are located as follows: the frontmost relay on the left inner fender is the high speed fan relay, the low speed fan relay is the rearmost, and the high speed fan ground relay is the inboard relay on the rear wall of the engine compartment. Let me know what you find.
Roland
*I don't understand the need for that switch but it gives the driver a way of turning on the fan manually.
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