P0128

DTC P0128 COOLANT THERMOSTAT (COOLANT TEMP. BELOW THERMOSTAT REGULATING TEMP.)

Component Location:

COMPONENT LOCATION

GENERAL DESCRIPTION

The coolant thermostat is located in the engine coolant passage of the cylinder head for regulating engine coolant temperature. When the engine coolant temperature reaches a specific temperature, the expansion element in the thermostat activates a valve, which redirects the flow of engine coolant into a radiator bypass line.

DTC DESCRIPTION

If the engine coolant temperature does not reach the specified value within the allocated period of time, the PCM determines that a malfunction exists and a DTC is stored.

DTC Detecting Condition:

DTC DETECTING CONDITION

Signal Waveform:

SIGNAL WAVEFORM

MONITOR SCANTOOL DATA

1. Ignition ON & Engine OFF




2. Monitor Engine Coolant Temperature Sensor parameter on Current data
3. Is Current data displayed correctly?

YES: Fault is intermittent caused by poor contact in the sensor's and/or PCM' S connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor con section,bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure.

NO: Go to "Component Inspection" procedure.

COMPONENT INSPECTION

1. Check Thermostat
1. Check cooling system coolant level and till if low.
2. Check for a proper cooling system operation. Especially check that cooling and condenser fan working normally.
3. Remove the thermostat and check the following items:
1. Stuck or damaged
2. Verify the temperature at which the valve begins to open. Initial valve opening temperature: 80 - 84 °(176-183.2 °F) Full valve opening temperature: 95 °C(203 °F)
4. Has a problem been found?

YES: Substitute with a known - good Thermostat and check for proper operation. If the problem is corrected, replace Thermostat and go to "Verification of Vehicle Repair" procedure.

NO: Substitute with a known - good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.

VERIFICATION OF VEHICLE REPAIR

After a repair, it is essential to verity that the fault has been corrected.
1. Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code(DTC) which has been diagnosed.
2. Using a Scantool, Clear the DTCs.
3. Operate the vehicle within conditions noted in the freeze frame data or enable conditions.
4. Monitor that all readiness test have been verified as "Complete"
5. Are any DTCs present?

YES: Go to the applicable trouble shooting procedure.

NO: System is performing to specification at this time.