Help us help you. By posting the year, make, model and engine near the beginning of your help request, followed by the symptoms (no start, high idle, misfire etc.) Along with any prevalent Diagnostic Trouble Codes, aka DTCs, other forum members will be able to help you get to a solution more quickly and easily!
My friend changed the spark plugs in his former police pursuit vehicle, and then upon start-up, the big electric radiator fan came on and stays on even while the engine is cold.
I determined fan relay #3 controls that fan, read that the ECM grounds the 85/86 circuit to turn the fan off, and was able to put 12 volts on relay pin # 86 which turns the fan off. However, once the key is cycled, the fan again turns on and stays on.
The coolant temperature gauge functions as does the speedometer. When I turn off the fan, activate the air conditioning, the fan functions as expected, but the fan will not turn off when the A/C is deactivated.
The fan can be turned off when the air conditioning is not functioning, so I believe AC conditions are not relevant here. Before my entering the picture, my friend replaced the IAT and coolant sensors in an attempt to fix the problem. I do not possess a scanner, so I do not know the IAT value, but the coolant dash readings are consistent with the previous values when the fan was not operating continuously. I suspect the computer is seeing the proper values (hot or cold) in that I can turn off the fan, and the fan stays off until the car is parked and then started again.
The only difference between before and after was the substitution of dual electrode spark plugs for the single electrode spark plugs that Dodge specifies. Thanks for your question.
Really not wise to post a full vin number in an open forum.
Based on experience with other vehicles most likely scennario is somewhere in the engine bay a wire will have an open got shorted or sensor disconneted as a result the engine computer is using a substituted value. Live data from even a low cost scantool would give a clue to the fan issue but the wiring to any of the temperature sensors or the AC pressure senor/trinary switch are prime suspects.
The P0450 is likely a different issue again live data would help but as it a circuit failure the wiring to the sensor or the sensor is suspects so start with powers and grounds at the sensor.
" We're trying to plug a hole in the universe, what are you doing ?. "
(Walter Bishop Fringe TV show)
Last edit: 6 years 8 months ago by Andy.MacFadyen.
Thank you for your reply. I questioned my friend about the possibility of a wire issue he may have caused while changing out the spark plugs, but he said he did not think so. Any recommendations for a low cost scan tool? I am old and not inclined to purchase one, but my friend has expressed an interest. Thanks again.
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