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Home >> Jeep >> 2007 >> Commander Overland, RWD >> Repair and Diagnosis >> Engine Performance >> System >> DTCS P0123 To P0174 >> P0128-Thermostat Rationality >> Possible Causes
July 1: So it begins. Don't worry, this is not in the correct legal jurisdiction!

Possible Causes

Possible Causes 
LOW COOLANT LEVEL
THERMOSTAT OPERATION
SIGNAL CIRCUIT SHORTED TO VOLTAGE
TEMPERATURE SENSOR
SIGNAL CIRCUIT OPEN
SENSOR GROUND CIRCUIT OPEN
SIGNAL CIRCUIT SHORTED TO GROUND
SIGNAL CIRCUIT SHORTED TO THE (K900), (G931) SENSOR GROUND CIRCUIT
OTHER POSSIBLE CAUSES
PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Refer to PRE-DIAGNOSTIC TROUBLESHOOTING PROCEDURE .