Problem: This vehicle came to the shop because
the temp gauge intermittently dropped to 165° F after engine had
completely warmed-up. The MIL (malfunction indicator light) was
Details: The tech connected a scan tool and
pulled a P0128 DTC (Engine coolant temperature sensor does not
meet the minimum thermostat regulating temperature in the pre-set
amount of time). The technician first replaced the ECT (Engine
coolant temperature) sensor and the thermostat with OEM parts but
the problem remained. On advice from the Tech-Assist consultant,
the technician checked the actual engine temperature with a
non-contact thermometer (laser infrared type) and compared that
temperature with the scan tool’s ECT PID. It was the same and
below the required threshold temperature.
Confirmed Repair: Because the technician had
already replaced the thermostat, the next possible cause was that
an incorrect radiator had been installed. NOTE:
Some replacement radiators may be missing a restricted orifice
that is built into the radiator tank, which is located in the
radiator hose fitting that feeds coolant to the surge tank. The
engine may not reach operating temperature or it may set DTC
P0128 due to excessive coolant flow to the radiator surge tank.
NOTE: If the actual temperature is correct and
the ECT sensor PID is incorrect then check the electrical circuit
and the connector pins for the ECT sensor. If the circuit and
connector are good, you may have a bad “New” sensor.
The tech confirmed that there was no restrictor in the radiator
fitting and that the radiator had been recently replaced. He
replaced the radiator with a different brand that had the
restrictor and the problem was solved.