P0128

DTC P0128 Thermostat Insufficient Temperature for Stable Operation




Circuit Description
- The engine coolant temperature (ECT) sensor thermistor mounted on a coolant crossover pipe at the front of the engine.

This code determines if system has insufficient coolant temperatures for stable operation.

Conditions for setting the DTC
- Engine running.
- No IAT, ECT and MAF DTCs set.
- No VSS DTC set.

Warm case (Ambient temperature is between 50 °F and 128 °F):
Time for coolant to reach stabilized closed loop value is less than 239 sec.

Cold case (Ambient temperature is between 20 °F and 50 °F):
Time for coolant to reach stabilized thermostat regulation temperature is more than 263 sec.

Action Taken When the DTC Sets
- The PCM will illuminate the malfunction indicator lamp(MIL) after the second consecutive trip in which the fault is detected.
- The PCM will store condition which were present when the DTC was set as Freeze Frame and in the Failure Records data.

Conditions for Clearing the MIL/DTC
- The PCM will turn the MIL "OFF" on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
- A history DTC P0128 will clear after 40 consecutive trip cycle during which the warm up cycles have occurred without a fault.
- DTC P0128 can be cleared using the Tech 2 "Clear Info" function or by disconnecting the PCM battery feed.

Tech 2 "Clear Info" function or by disconnecting the PCM battery feed.

Diagnostic Aids
An intermittent may be caused by the following:
- Poor connections.
- Misrouted harness.
- Rubbed through wire insulation.
- Broken wire inside the insulation. Check for the following conditions:
- Poor connection at PCM - Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
- Damaged harness - Inspect the wiring harness for damage.

If the harness appears to be OK, observe the ECT display on the Tech 2 while moving connectors and wiring harnesses related to the sensor.

A change in the display will indicate the location of the fault.

If DTC P0128 cannot be duplicated, the information included in the Failure Records data can be useful in determined vehicle mileage since the DTC was last set.

If it is determined that the DTC occurs intermittently, performing the DTC P0128 Diagnostic Chart may isolate the cause of the fault.

Steps 1 - 4:

Steps 5 - 8:

Test Description