[Previous][Next]
DTC P0125-00: Coolant TEMP. sensor insufficient for closed loop fuel control
 
 
 
 
CIRCUIT OPERATION
  • A power voltage of 5 volts is applied to the engine coolant temperature sensor connector terminal number 1 from the ECM connector terminal number 38.
  • The power voltage is grounded to the ECM connector terminal number 28 from the engine coolant temperature sensor connector terminal number 2.
  • 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
Once per driving cycle.
 
 
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC set in memory for the item monitored below)
  • Not applicable
Sensor (The sensor below is determined to be normal)
  • Not applicable
 
 
DTC SET CONDITIONS
Logic Flow Chart
Check Conditions
  • Approximately 90 to 300 seconds have passed for the engine coolant temperature to rise to approximately 8°C (46°F) after starting sequence was completed.
  • However, time is not counted when fuel is shut off.
Judgment Criteria
  • Engine coolant temperature decreases from more than 40°C (104°F) to less than 40°C (104°F).
  • Then the engine coolant temperature is less than 40°C (104°F) for 5 minutes.
 
 
FAIL-SAFE AND BACKUP FUNCTION
None.
 
 
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function, OBD-II Drive Cycle – Pattern 2 OBD- II DRIVE CYCLE.
 
 
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are:)
  • Engine coolant temperature sensor failed.
  • Engine coolant temperature sensor circuit harness damage or connector damage.
  • ECM failed.
 
 
DIAGNOSIS
Required Special Tools:
  • MB992744: Vehicle communication interface-Lite (V.C.I.-Lite)
  • MB992745: V.C.I.-Lite main harness A
  • MB992747: V.C.I.-Lite USB cable short
  • MB992748: V.C.I.-Lite USB cable long
  • MB991658: Test harness
1.STEP 1. Using scan tool (M.U.T.-III SE), check the data list.
Use scan tool (M.U.T.-III SE) to check the data list (Refer to DATA LIST REFERENCE TABLE).
  • Item number 60: Coolant (Water) Temperature Sensor
Q: Is the check result normal?
 
2.STEP 2. Perform voltage measurement at engine coolant temperature sensor connector terminal number 1.
  • Disconnect connector, and connect the test harness special tool MB991658 between the separated connectors.
  • Power supply mode of electric motor switch: ON
  • Voltage between engine coolant temperature sensor connector terminal number 1 and ground.
OK
  • When engine coolant temperature is –20°C (–4°F), voltage should be between 3.9 and 4.5 volts.
  • When engine coolant temperature is 0°C (32°F), voltage should be between 3.2 and 3.8 volts.
  • When engine coolant temperature is 20°C (68°F), voltage should be between 2.3 and 2.9 volts.
  • When engine coolant temperature is 40°C (104°F), voltage should be between 1.3 and 1.9 volts.
  • When engine coolant temperature is 60°C (140°F), voltage should be between 0.7 and 1.3 volts.
  • When engine coolant temperature is 80°C (176°F), voltage should be between 0.3 and 0.9 volt.
Q: Is the check result normal?
 
3.STEP 3. Using scan tool (M.U.T.-III SE), check the data list.
Use scan tool (M.U.T.-III SE) to check the data list (Refer to DATA LIST REFERENCE TABLE).
  • Item number 60: Coolant (Water) Temperature Sensor
Q: Is the check result normal?
Replace the ECM (Refer to ENGINE CONTROL MODULE (ECM) REMOVAL AND INSTALLATION).
 
4.STEP 4. Perform voltage measurement at engine coolant temperature sensor connector terminal number 1.
  • Disconnect connector, and measure at harness side.
  • Power supply mode of electric motor switch: ON
  • Voltage between engine coolant temperature sensor connector terminal number 1 and ground.
OK: 4.9 to 5.1 volts
Q: Is the check result normal?
 
5.STEP 5. Check harness between engine coolant temperature sensor connector terminal number 1 and ECM connector terminal number 38.
Check power supply line for damage.
Q: Is the check result normal?
Repair or replace the connector, or repair the damaged harness wire.
 
6.STEP 6. Perform resistance measurement at engine coolant temperature sensor connector terminal number 2.
  • Disconnect connector, and measure at harness side.
  • Resistance between engine coolant temperature sensor connector terminal number 2 and ground.
OK: Continuity (2 ohms or less)
Q: Is the check result normal?
 
7.STEP 7. Check harness between engine coolant temperature sensor connector terminal number 2 and ECM connector terminal number 28.
Check ground line for open circuit and damage.
Q: Is the check result normal?
Repair or replace the connector, or repair the damaged harness wire.
 
8.STEP 8. Check engine coolant temperature sensor itself.
Check engine coolant temperature sensor itself (Refer to ENGINE COOLANT TEMPERATURE SENSOR CHECK).
Q: Is the check result normal?
Replace the engine coolant temperature sensor (Refer to ENGINE, Engine Cooling – Water Hose and Water Pipe WATER HOSE AND WATER PIPE REMOVAL AND INSTALLATION).
 
9.STEP 9. Test the OBD-II drive cycle.
After erasing the DTC, carry out test drive with the drive cycle pattern, and recheck the DTC.
(1) Use scan tool (M.U.T.-III SE) to erase the DTC.
(2) Carry out test drive with the drive cycle pattern (Refer to Diagnostic Function, OBD-II Drive Cycle – Pattern 2 OBD- II DRIVE CYCLE).
(3) Use scan tool (M.U.T.-III SE) to recheck the DTC.
Q: Is DTC P0125-00 set?
Replace the ECM (Refer to ENGINE CONTROL MODULE (ECM) REMOVAL AND INSTALLATION).
Intermittent malfunction (Refer to GENERAL INFORMATION, General Information – How to Use Troubleshooting/Inspection Service Points – How to Cope with Intermittent Malfunctions HOW TO COPE WITH INTERMITTENT MALFUNCTIONS).