P0125
Engine Coolant Temperature Sensor Circuit:
CIRCUIT OPERATION
- 5-volt voltage is applied to the engine coolant temperature sensor output terminal (terminal 1) from the ECM (terminal 83)
- The engine coolant temperature sensor is a negative temperature coefficient type of resistor. It has the characteristic that when the engine coolant temperature rises the resistor decreases.
- The engine coolant temperature sensor output voltage increases when the resistor increases and decreases when the resistor decreases.
TECHNICAL DESCRIPTION
- The engine coolant temperature sensor converts the engine coolant temperature to a voltage and output it.
- The ECM
DTC SET CONDITIONS
Check Conditions, Judgement Criteria
- Engine coolant temperature decreases from higher than 40 °C (104 °F) to lower than 40 °C (104 °F).
- Then the engine coolant temperature has continued to be 40 °C (104 °F) or lower for five minutes.
Check Conditions, Judgement Criteria
- About 60 - 300 seconds have passed for the engine coolant temperature to rise to about 7 °C (44.6 °F) after starting sequence was completed.
- However, time is not counted when fuel is shut off.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Engine coolant temperature sensor failed.
- Open or shorted engine coolant temperature sensor circuit, or loose connector.
- ECM failed.
- PCM failed.
DIAGNOSIS
Required Special Tools
- MB991502: Scan Tool (MUT-II)
STEP 1. Using scan tool MB991502, check data list item 21: Engine Coolant Temperature Sensor.
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991502 to the data reading mode for item 21, Engine Coolant Temperature Sensor.
- The engine coolant temperature and temperature shown with the scan tool should approximately match.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points.
NO: Go to Step 2.
STEP 2. Check the sensor output voltage at engine coolant temperature sensor connector B-107 by backprobing.
1. Do not disconnect the connector B-107.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal 1 and ground by backprobing.
- When engine coolant temperature is -20 °C (-4 °F), voltage should be 3.9 and 4.5 volts.
- When engine coolant temperature is 0 °C (32 °F), voltage should be 3.2 and 3.8 volts.
- When engine coolant temperature is 20 °C (68 °F), voltage should be 2.3 and 2.9 volts.
- When engine coolant temperature is 40 °C (104 °F), voltage should be 1.3 and 1.9 volts.
- When engine coolant temperature is 60 °C (140 °F), voltage should be 0.7 and 1.3 volts.
- When engine coolant temperature is 80 °C (176 °F), voltage should be 0.3 and 0.9 volt.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the voltage normal?
YES: Go to Step 3.
NO: Go to Step 5.
STEP 3. Check connector B-107 at the engine coolant temperature sensor for damage.
Q: Is the connector in good condition?
YES: Go to Step 4.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 4. Using scan tool MB991502, check data list item 21: Engine Coolant Temperature Sensor.
CAUTION: To prevent damage to scan tool MB991502, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991502.
1. Connect scan tool MB991502 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991502 to the data reading mode for item 21, Engine Coolant Temperature Sensor.
- The engine coolant temperature and temperature shown with the scan tool should approximately match.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the sensor operating properly?
YES: It can be assumed that this malfunction is intermittent. Refer to How to Use Troubleshooting/Inspection Service Points.
NO: Replace the ECM or PCM. Then go to Step 14.
STEP 5. Check connector B-107 at engine coolant temperature sensor for damage.
Q: Is the connector in good condition?
YES: Go to Step 6.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 6. Check the sensor supply voltage at engine coolant temperature sensor harness side connector B-107.
1. Disconnect the connector B-107 and measure at the harness side.
2. Turn the ignition switch to the "ON" position.
3. Measure the voltage between terminal 1 and ground.
- Voltage should be between 4.5 and 4.9 volts.
4. Turn the ignition switch to the "LOCK" (OFF) position.
Q: Is the voltage normal?
YES: Go to Step 8.
NO: Go to Step 7.
STEP 7. Check connector C-115 at ECM
Q: Is the connector in good condition?
YES: Replace the ECM or PCM. Then go to Step 14.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 8. Check the continuity at engine coolant temperature sensor harness side connector B-107.
1. Disconnect the connector B-107 and measure at the harness side.
2. Check for the continuity between terminal 2 and ground.
- Should be less than 2 ohm.
Q: Is the continuity normal?
YES: Go to Step 11.
NO: Go to Step 9.
STEP 9. Check connector C-115 at ECM
Q: Is the connector in good condition?
YES: Go to Step 10.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 10. Check for harness damage between engine coolant temperature sensor connector B-107 terminal 2 and ECM connector C-115 terminal 92
Q: Is the harness wire in good condition?
YES: Replace the ECM or PCM. Then go to Step 14.
NO: Repair it. Then go to Step 14.
STEP 11. Check the engine coolant temperature sensor.
1. Disconnect the engine coolant temperature sensor connector B-107.
2. Remove the engine coolant temperature sensor
3. With the temperature sensing portion of engine coolant temperature sensor immersed in hot water, check resistance.
Standard value:
14 - 17 kohm [at -20 °C (-4 °F)]
5.1 - 6.5 kohm [at 0 °C (32 °F)]
2.1 - 2.7 kohm [at 20 °C (68 °F)]
0.9 - 1.3 kohm [at 40 °C (104 °F)]
0.48 - 0.68 kohm [at 60 °C (140 °F)]
0.26 - 0.36 kohm [at 80 °C (176 °F)]
4. Apply 3M(TM) AAD part number 8731 or equivalent on the screw section of the engine coolant temperature sensor
5. Install the engine coolant temperature sensor, and tighten to the specified torque.
Tightening torque: 29 ± 10 N.m (22 ± 7 ft-lb)
Q: Is the resistance at the standard value?
YES: Go to Step 12.
NO: Replace the engine coolant temperature sensor. Then go to Step 14.
STEP 12. Check connector C-115 at ECM
Q: Is the connector in good condition?
YES: Go to Step 13.
NO: Repair or replace it. Refer to Harness Connector Inspection. Then go to Step 14.
STEP 13. Check for harness damage between engine coolant temperature sensor connector B-107 terminal 1 and ECM connector C-115 terminal 83
Q: Is the harness wire in good condition?
YES: Replace the ECM or PCM. Then go to Step 14.
NO: Repair it. Then go to Step 14.
STEP 14. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to, Procedure 6 - Other Monitor.
2. Check the diagnostic trouble code (DTC).
Q: Is the DTC P0125 output?
YES: Retry the troubleshooting.
NO: The inspection is complete.