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DTC P0118: Engine
Coolant Temperature Circuit High Input
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 is out
of specified range.
MONITOR EXECUTION
MONITOR EXECUTION CONDITIONS (Other monitor and Sensor)
Other Monitor (There is no temporary DTC stored in memory
for the item monitored below)
Sensor (The sensor below is determined to be normal)
DTC SET CONDITIONS
Logic Flow Chart
Check Condition
- More than 2 seconds have passed since the engine starting sequence was completed.
Judgement Criterion
- Engine coolant temperature sensor output voltage is more than 4.6 volts for 2 seconds.
FAIL-SAFE AND BACKUP FUNCTION
- Control as if the engine coolant temperature is 80 °C
(176°F).
OBD-II DRIVE CYCLE PATTERN
Refer to Diagnostic Function-OBD-II Drive Cycle-Pattern
23 
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TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )
- Engine coolant temperature sensor failed.
- Open engine coolant temperature sensor circuit, or connector damage.
- ECM failed.
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Required Special Tools:
- MB991958: Scan Tool (M.U.T.-III Sub Assembly)
- MB991824: V.C.I.
- MB991827: USB Cable
- MB991910: Main Harness A
- MB992110: Power Plant ECU Check Harness
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STEP 1. Using scan tool MB991958, check data list item
6: Engine Coolant Temperature Sensor.
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To prevent damage to scan tool MB991958, always turn the ignition switch to the "LOCK"
(OFF) position before connecting or disconnecting scan tool MB991958.
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(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?
 It can be assumed that this malfunction is intermittent. Refer to GROUP 00, How
to Use Troubleshooting/Inspection Service Points - How to Cope with Intermittent
Malfunctions .
 Go to Step 2.
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STEP 2. Check harness connector B-06 at engine coolant temperature
sensor for damage.
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Q.
Is the harness connector in good condition?
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Go to Step 3.
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Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection .
Then go to Step 10.
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STEP 3. Measure the sensor supply voltage at engine coolant temperature
sensor harness side connector B-06.
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(1)Disconnect the connector B-06 and measure at the harness side.
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(2)Turn the ignition switch to the "ON" position.
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(3)Measure the voltage between terminal No. 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 measured voltage between 4.5 and 4.9 volts?
Go to Step 6.
Go to Step 4.
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STEP 4. Check harness connector B-108 at ECM for damage.
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Q.
Is the harness connector in good condition?
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Go to Step 5.
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Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection .
Then go to Step 10.
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STEP 5. Measure the sensor supply voltage at ECM connector B-108 by
using power plant ECU check harness special tool MB992110.
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(1)Disconnect all ECM connectors. Connect the power plant ECU check harness special tool
MB992110 between the separated connectors.
(2)Disconnect the engine coolant temperature sensor connector B-06.
(3)Turn the ignition switch to the "ON" position.
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(4)Measure the voltage between terminal No. 26 and ground.
- Voltage should be between 4.5 and 4.9 volts.
(5)Turn the ignition switch to the "LOCK" (OFF) position.
Q.
Is the measured voltage between 4.5 and 4.9 volts?
Repair harness wire between engine coolant temperature sensor connector B-06 (terminal
No. 1) and ECM connector B-108 (terminal No. 26) because of open circuit. Then go to Step 10.
Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP
42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or
GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> .
Then go to Step 10.
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STEP 6. Check the continuity at engine coolant temperature sensor
harness side connector B-06.
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(1)Disconnect the connector B-06 and measure at the harness side.
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(2)Check for the continuity between terminal No. 2 and ground.
- Continuity (2 ohms or less)
Q.
Does continuity exist?
Go to Step 9.
Go to Step 7.
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STEP 7. Check harness connector B-108 at ECM for damage.
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Q.
Is the harness connector in good condition?
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Go to Step 8.
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Repair or replace it. Refer to GROUP 00E, Harness Connector Inspection .
Then go to Step 10.
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STEP 8. Check for open circuit between engine coolant temperature
sensor connector B-06 (terminal No. 2) and ECM connector B-108 (terminal No. 27).
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Q.
Is the harness wire in good condition?
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Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP
42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or
GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> .
Then go to Step10.
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Repair it. Then go to Step 10.
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STEP 9. Check the engine coolant temperature sensor.
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Refer to Engine Coolant Temperature Sensor Check .
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Q.
Is the engine coolant temperature sensor normal?
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Replace the ECM. When the ECM is replaced, register the ID code. Refer to GROUP
42B, Diagnosis - ID Code Registration Necessity Judgment Table <Vehicles with KOS> or
GROUP 42C, Diagnosis - ID Codes Registration Judgment Table <Vehicles with WCM> .
Then go to Step 10.
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Replace the engine coolant temperature sensor. Then go to Step 10.
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STEP 10. Test the OBD-II drive cycle.
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(1)Carry out a test drive with the drive cycle pattern. Refer to Diagnostic Function - OBD-II
Drive Cycle - Pattern 23 .
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(2)Check the diagnostic trouble code (DTC).
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Retry the troubleshooting.
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The inspection is complete.
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