P0128

DTC P0128: Coolant Thermostat

DTC Detecting Condition and Trouble Area






DTC Confirmation Procedure

WARNING:

- When performing a road test, select a place where there is no traffic or possibility of a traffic accident and be very careful during testing to avoid occurrence of an accident.
- Road test should be carried out with 2 persons, a driver and a tester, on a level road.

NOTE:

Check to make sure that the following conditions are satisfied when using this DTC confirmation procedure.

- Intake air temp.: -14 °C, 6.8 °F or higher
- Altitude (barometric pressure): 2020 m, 6650 ft or less (540 mmHg, 72 kPa or more)

1) With ignition switch turned OFF, connect scan tool to DLC.
2) Turn ON ignition switch and clear DTC using scan tool.
3) Start engine and drive vehicle in 40 - 60 km/h (25 - 40 mile/h) vehicle speed and 2000 - 3000 rpm engine speed for 20 minutes or more.
4) Stop vehicle and check DTC and pending DTC.

DTC Troubleshooting

1.
Was "Engine System Check" performed?
YES
Go to Step 2.
NO
Go to Engine System Check Engine System Check.

2. Engine coolant temp. check.

With ignition switch turned OFF, install scan tool.
Turn ON ignition switch and check engine coolant temp. displayed on scan tool.
Warm up engine to normal operating temp. and check engine coolant temp. displayed on scan tool.

Does engine coolant temp. vary higher than 1 °C (1 °F) and rise higher than 75 °C (167 °F)?
YES
Intermittent trouble.
Check for intermittent referring to Intermittent and Poor Connection Inspection.
NO
Go to Step 3.

3. Check ECT sensor harness voltage.

Disconnect connectors from ECT sensor and ECM with ignition switch turned OFF.
Turn ON ignition switch.
Check voltage between "LT GRN" wire terminal in ECT sensor harness connector and vehicle body ground.

Is voltage about 0 V at each terminal?
YES
Go to Step 4.
NO
"LT GRN" wire shorted to others circuit.
If wire are OK, substitute a known-good ECM and recheck.

4. Check ECT sensor harness resistance.

Measure resistance between "C46-12" terminal and "LT GRN" wire terminal in ECT sensor connector with ignition switch turned OFF.

Is resistance below 5 ohms?
YES
Go to Step 5.
NO
"LT GRN" wire in high resistance circuit.

5. Check ECT sensor ground circuit.

Connect connector to ECM.
Check proper connection of ECT sensor at "ORN" wire terminal.
Measure resistance between "ORN" wire terminal in ECT sensor connector and vehicle body ground.

Is resistance below 10 ohms?
YES
Go to Step 7.
NO
Go to Step 6.

6. Check ECT sensor ground circuit.

Measure resistance between "C46-27" terminal and vehicle body ground.

Is resistance below 5 ohms?
YES
"ORN" wire open circuit or high resistance circuit.
Poor "C46-27" connection.
NO
Faulty ECM ground circuit.
If circuit are OK, substitute a known-good ECM and recheck.

7. Check ECT sensor.

Check ECT sensor according to Engine Coolant Temperature (ECT) Sensor Inspection Engine Coolant Temperature (ECT) Sensor Inspection.

Is it good condition?
YES
Go to Step 8.
NO
Replace ECT sensor.

8. Thermostat Check.

Is there a symptom due to thermostat remaining open (it takes a long time before vehicle heater becomes effective or before engine is warmed to normal operating temp., etc.)?
YES
Check thermostat referring to Thermostat Inspection.
NO
Faulty ECM. Substitute a known-good ECM and recheck.