Question about 2004 Jeep Grand Cherokee
Check engine light code on for engine coolant temperature sensor replaced sensor and thermostat reset computer same code came back and temperature gauge fluctuating hot to cold
Check continuity of the sensor wire. It should run between pin #4 (check manual (chilton better than haynes for electrical) for location as sometimes there are design changes) of the black harness plug on the computer to the sensor. The other sensor wire is shared with the cps and tps sensors, so if you don't see problem readings with those that wire is likely good.
Also, make sure that you have no air in the cooling system or as it passes the sensor it can mess with the readings. Run the engine with the system open and the heat on high....I like doing this with the front of the vehicle either jacked up slightly or pointing up-hill... run a complete "cycle" from cold to operating temp and add coolant as needed.
Hope this helps!
Posted on May 12, 2010
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Posted on Jan 02, 2017
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This means that the engine's PCM detected that the engine has not reached the required temperature level within a specified amount of time after starting the engine. The intent of the P0128 code is to indicate a faulty thermostat. Similar codes: P0125
In determining the engine did not reach a "normal" temperature, it takes into account the length of time the vehicle has been running, the intake air temperature (IAT) sensor reading, the engine coolant temperature (ECT) sensor reading, and the speed of the vehicle.
A code P0128 may mean that one or more of the following has happened:
Past experience indicates that the most likely solution is to replace the thermostat. However here are some suggestions on troubleshooting and repairing a P0128 OBD-II code:
I hope this helps a bit!
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