P0125
DTC P0125: Insufficient Coolant Temperature for Closed Loop Fuel ControlEngine Coolant Temperature Sensor Circuit (Part 1):
Engine Coolant Temperature Sensor Circuit (Part 2):
CIRCUIT OPERATION
- 5-volt voltage is applied to the engine coolant temperature sensor output terminal (terminal No. 1) from the ECM (terminal No. 26) via the resistor in the ECM. The ground terminal (terminal No. 2) is grounded with ECM (terminal No. 27).
- 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 resistance decreases.
- The engine coolant temperature sensor output voltage increases when the resistance increases and decreases when the resistance decreases.
TECHNICAL DESCRIPTION
- The engine coolant temperature sensor converts the engine coolant temperature to a voltage and outputs it.
- The ECM checks whether this voltage is within a specified range.
DESCRIPTIONS OF MONITOR METHODS
- Engine coolant temperature sensor output voltage drops from over 40 °C (104 °F) to under 40 °C (104 °F) and keeps under 40 °C (104 °F) for 5 minutes.
- Engine coolant temperature sensor output voltage does not reach close loop enable temperature within specified period when engine coolant temperature sensor output voltage at engine start is under 7 °C (45 °F).
MONITOR EXECUTION
Continuous
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC stored in memory for the item monitored below)
- Not applicable
Sensor (The sensor below is determined to be normal)
- Mass air flow sensor
- Intake air temperature sensor
DTC SET CONDITIONS [Range/Performance problem - low input (time to reach closed loop temperature)]
Logic Flow Chart:
Check Conditions, Judgement Criteria
- About 90 - 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.
DTC SET CONDITIONS [Range/Performance problem - drift]
Logic Flow Chart:
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 5 minutes.
OBD-II DRIVE CYCLE PATTERN
Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 9. OBD-II Drive Cycle
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
- Engine coolant temperature sensor failed.
- Harness damage
- Connector damage
- ECM failed.
DIAGNOSIS
Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A
STEP 1. Using scan tool MB991958, check data list item 6: Engine Coolant Temperature Sensor.
CAUTION: To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK" (OFF) position before connecting or disconnecting scan tool MB991958.
1. Connect scan tool MB991958 to the data link connector.
2. Turn the ignition switch to the "ON" position.
3. Set scan tool MB991958 to the data reading mode for item 6, 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 General (Body and Chassis), How to Use Troubleshooting/Inspection Service Points-How to Cope with Intermittent Malfunctions.
NO : Go to Step 2.
STEP 2. Check harness connector B-09 at the engine coolant temperature sensor and harness connector B-10 at the ECM for damage.
Q: Is the harness connector in good condition?
YES : Go to Step 3.
NO : Repair it. Refer to General (Electrical), Harness Connector Inspection. Then go to Step 5.
STEP 3. Check for harness between the engine coolant temperature sensor connector B-09 and the ECM connector B-10.
1. Disconnect the engine coolant temperature sensor connector B-09 and the ECM connector B-10.
2. Measure the resistance between the engine coolant temperature sensor connector B-09 and the ECM connector B-10.
a. Connector B-09 (terminal No. 1) and Connector B-10 (terminal No. 26).
b. Connector B-09 (terminal No. 2) and Connector B-10 (terminal No. 27).
- Should be less than 2 ohms.
Q: Is the harness wire in good condition?
YES : Go to Step 4.
NO : Repair it. Then go to Step 5.
STEP 4. Check the engine coolant temperature sensor.
1. Disconnect the engine coolant temperature sensor connector B-09.
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 kohms [at -20 °C (-4 °F)]
5.1 - 6.5 kohms [at 0 °C (32 °F)]
2.1 - 2.7 kohms [at 20 °C (68 °F)]
0.9 - 1.3 kohms [at 40 °C (104 °F)]
0.48 - 0.68 kohms [at 60 °C (140 °F)]
0.26 - 0.36 kohms [at 80 °C (176 °F)]
4. Apply 3M"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 measured resistance at the standard value?
YES : Go to Step 5.
NO : Replace the engine coolant temperature sensor. Then go to Step 5.
STEP 5. Test the OBD-II drive cycle.
1. Carry out a test drive with the drive cycle pattern. Refer to MFI Diagnostic Function-OBD-II Drive Cycle-Pattern 9. OBD-II Drive Cycle
2. Check the diagnostic trouble code (DTC).
Q: Is DTC P0125 set?
YES : Replace the ECM. When the ECM is replaced,register the ID code. Refer to Diagnosis-ID Codes Registration Judgment Table [Vehicles with KOS] or Diagnosis-ID Codes Registration Judgment Table [Vehicles with WCM].
NO : It can be assumed that this malfunction is intermittent. Refer to General (Body and Chassis), How to Use Troubleshooting/Inspection Service Points How to Cope with Intermittent Malfunctions.