Engine Coolant Temperature
The engine coolant temperature (ECT) sensor (Figure 25) is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as the temperature increases, and increases as the temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in a series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The ECT measures the temperature of the engine coolant. The sensor is threaded into an engine coolant passage. The ECT sensor is similar in construction to the IAT sensor
Cylinder Head Temperature Sensor
The cylinder head temperature (CHT) sensor (Figure 24) is a thermistor device in which resistance changes with temperature. The electrical resistance of a thermistor decreases as temperature increases, and increases as temperature decreases. The varying resistance affects the voltage drop across the sensor terminals and provides electrical signals to the PCM corresponding to temperature.
Thermistor-type sensors are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying the resistance of the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal to the reference voltage minus the voltage drop across the fixed resistor.
The cylinder head temperature (CHT) sensor is installed in the aluminum cylinder head and measures the metal temperature. The CHT sensor communicates an overheating condition to the PCM. The PCM would then initiate a cooling strategy based on information from the CHT sensor. A cooling system failure such as low coolant or coolant loss could cause an overheating condition. As a result, damage to major engine components could occur. Using a CHT sensor and cooling strategy would prevent damage by allowing air cooling of the engine and limp home capability.
DA1 DTC P1116: CHECK OPERATION OF ECT SENSOR
Run engine at 2000 rpm until engine temperature becomes stabilized.
No Starts:
GO to DA3 .
Vehicles that stall:
Return to Section 3 , Symptom Charts.
Check that upper radiator hose is hot and pressurized.
Rerun Key On Engine Running (KOER) Self-Test.
Is DTC P1116 present?
Yes No
GO to DA2 . KEY OFF. Engine was not at closed loop operating conditions. REPAIR any other DTCs as necessary.
DA2 CHECK VREF VOLTAGE TO TP SENSOR
Refer to schematic at the beginning of the Pinpoint Test.
Disconnect throttle position (TP) sensor.
Key on, engine off.
Measure the voltage between VREF and SIG RTN circuits at the TP sensor harness connector.
Is voltage between 4.0 volts and 6.0 volts?
Yes No
There is sufficient VREF voltage. RECONNECT TP sensor. GO to DA3 . GO to Pinpoint Test Step C1 .
DA3 CHECK TEMPERATURE SENSOR RESISTANCE WITH ENGINE OFF
Disconnect ECT sensor.
Measure ECT sensor resistance. Refer to the chart at the beginning of this Pinpoint Test for resistance specifications.
Is resistance within specification?
Yes No
For ECT sensor with a No Start:
Do not repair DTC P1116 at this time. RETURN to Section 3 , Symptom Charts.
For symptoms of cooling fan concerns, overheating and lack of heat, do not repair DTC P1116. REPAIR next DTC. If no other DTC exists, RETURN to Section 3 , Symptom Charts.
All others:
GO to DA4 . REPLACE suspect sensor.
DA4 CHECK TEMPERATURE SENSOR RESISTANCE WITH ENGINE RUNNING
Note: Verify that engine is at operating temperature before taking ECT readings.
Run engine for two minutes at 2000 rpm.
Measure temperature sensor resistance. Refer to the chart at the beginning of this Pinpoint Test for resistance specifications.
Is resistance within specification?
Yes No
REPLACE PCM (refer to Section 2 , Flash EEPROM). RESTORE vehicle. REPLACE suspect sensor.
DA10 DTC P0118 OR P0113: CHECK FOR SHORT TO VPWR OR VREF
Key off.
Disconnect harness from applicable temperature sensor.
Key on.
Is the applicable temperature sensor voltage PID greater than 4.8 volts?
Yes No
GO to DA13 . GO to DA11 . KEY OFF.
DA11 SIMULATE OPPOSITE SIGNAL TO PCM
With applicable temperature sensor disconnected, connect a jumper wire between the sensor signal and SIG RTN circuits at the temperature sensor harness connector.
Key on.
Note: If a scan tool communication concern exists, remove jumper wire immediately and GO to DA13 .
Access applicable temperature sensor voltage PID.
Is the applicable temperature sensor voltage PID less than 0.2 volts (greater than 120°C/248°F)?
Yes No
REPLACE suspect sensor. REMOVE jumper wire. GO to DA12 . KEY OFF.
DA12 CHECK TEMPERATURE SENSOR SIGNAL AND SIG RTN CIRCUITS FOR OPEN IN HARNESS
Note: Refer to the PCM connector pin numbers on this pinpoint test cover page.
Disconnect PCM.
Measure resistance of sensor signal circuit between PCM harness connector pin and applicable sensor harness connector.
Measure resistance of SIG RTN circuit between PCM harness connector pin and applicable temperature sensor harness connector.
Is each resistance less than 5.0 ohms?
Yes No
REPLACE PCM (refer to Section 2 , Flash EEPROM). REPAIR open circuits.
DA13 CHECK TEMPERATURE SIGNAL FOR SHORT TO VPWR OR VREF
Key on.
Measure voltage between applicable temperature signal circuit at the sensor harness connector and chassis ground.
Is voltage greater than 4.8 volts?
Yes No
REPAIR short to VREF or VPWR in harness. If harness is OK, REPLACE PCM (refer to Section 2 , Flash EEPROM). GO to C5 .
DA20 DTC P0112 OR P0117: SIMULATE OPPOSITE SIGNAL TO PCM
Disconnect harness from applicable temperature sensor.
Connect scan tool.
Key on.
Access applicable temperature sensor voltage PID.
Key off.
Is the applicable temperature sensor voltage PID greater than 4.2 volts (less than -40°C/-40°F)?
Yes No
REPLACE sensor. GO to DA21 .
DA21 CHECK VREF VOLTAGE TO TP SENSOR
Refer to schematic at the beginning of the pinpoint test.
Disconnect TP sensor.
Key on, engine off.
Measure the voltage between VREF and SIG RTN circuits at the TP sensor harness connector.
Is voltage between 4.0 and 6.0 volts?
Yes No
There is sufficient VREF voltage. RECONNECT TP sensor. GO to DA22 . KEY OFF. GO to Pinpoint Test Step C1 .
DA22 CHECK TEMPERATURE SIGNAL CIRCUIT FOR SHORT TO GROUND IN HARNESS
Note: Refer to the PCM connector pin numbers on this pinpoint test cover page.
Disconnect PCM.
Measure resistance between sensor signal and SIG RTN circuits and then between sensor signal and PWR GND circuits at the PCM harness connector.
Is each resistance greater than 10,000 ohms?
Yes No
REPLACE PCM (refer to Section 2 , Flash EEPROM). REPAIR short circuit.
DA90 DTCS P0112, P1112, P0113, P0117, P1117 OR P0118: INTERMITTENT CHECK
Connect scan tool.
Key on.
Monitor the applicable temperature sensor voltage PID.
While observing the PID, complete the following:
Tap on the sensor to simulate road shock.
Wiggle the sensor connector.
Is there any large change in the voltage reading?
Yes No
Key OFF. DISCONNECT and INSPECT connectors. If OK, REPLACE the sensor. For Continuous DTCs P1112 and P1117, COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles). GO to DA91 .
DA91 CHECK ELECTRONIC ENGINE CONTROL (EC) WIRING HARNESS
Still monitoring PID.
While observing the appropriate PID, complete the following:
Hold the sensor harness close to the sensor connector. Wiggle, shake and bend small sections of wiring harness while working toward the PCM.
Is there any change in the voltage reading?
Yes No
ISOLATE fault. REPAIR as necessary. For Continuous DTCs P1112 and P1117, COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles). GO to DA92 .
DA92 CHECK PCM AND VEHICLE HARNESS CONNECTOR
Disconnect PCM.
Disconnect sensor connector.
Are connectors and terminals OK?
Yes No
Fault is not present at this time. For Continuous Memory DTCs P1112 and P1117, COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles). REPAIR as necessary. For Continuous Memory DTCs P1112 or P1117, COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles).
DA100 DTC P0125: CHECK ENGINE COOLANT LEVEL
Diagnostic Trouble Code (DTC) P0125 indicates the ECT sensor has not achieved the required temperature level to enter closed loop operating conditions within a specified amount of time after starting engine. This DTC will light the MIL.
Possible Causes:
Insufficient warm up time.
Leaky or stuck open thermostat.
Low engine coolant level.
Malfunctioning ECT sensor.
WARNING: TO AVOID PERSONAL INJURY, DO NOT UNSCREW THE COOLANT PRESSURE RELIEF CAP WHILE THE ENGINE IS OPERATING OR HOT. THE COOLANT SYSTEM IS UNDER PRESSURE; STEAM AND HOT LIQUID CAN COME OUT FORCEFULLY WHEN THE CAP IS LOOSENED SLIGHTLY.
Check engine coolant level.
Is the engine coolant level fill correct?
Yes No
GO to Engine Cooling, Section 303-03 in the Workshop Manual for further diagnostics. FILL engine coolant to proper level. COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles).
DA110 DTC P1184: CHECK OPERATION OF EOT TEMP SENSOR
Connect scan tool.
Run engine at 2000 rpm until engine temperature becomes stabilized.
Run Key On Engine Running (KOER) Self-Test.
Is DTC P1184 present?
Yes No
GO to DA111 . Engine oil temperature was not at operating temperature. REPAIR any other DTCs as necessary.
DA111 DTC P1183, P1184 OR P0298: CHECK TEMPERATURE SENSOR SIGNAL
Connect scan tool.
Key on.
Access EOTV PID.
Is EOTV PID less than 0.3 volts?
Yes No
GO to DA112 . GO to DA115 .
DA112 SIMULATE OPPOSITE EOT SIGNAL TO PCM
Still monitoring PID.
Disconnect EOT sensor.
Is EOTV PID greater than 4.2 volts?
Yes No
REPLACE suspect sensor. GO to DA113 .
DA113 CHECK EOT SIGNAL CIRCUIT FOR SHORT TO GROUND IN HARNESS
Note: Refer to the PCM connector pins numbers on this pinpoint test cover page.
Disconnect PCM.
Measure resistance between EOT and SIG RTN circuits and then between EOT and PWR GND circuits at the PCM harness connector.
Is each resistance greater than 10,000 ohms?
Yes No
REPLACE PCM (refer to Section 2 , Flash EEPROM). REPAIR short circuit.
DA115 CHECK FOR HIGH EOT SIGNAL
Still monitoring PID.
Is EOTV PID greater than 4.2 volts?
Yes No
GO to DA116 . GO to DA120 .
DA116 SIMULATE LOW SIGNAL TO PCM
Disconnect EOT temperature sensor.
Connect a jumper wire between the sensor signal and SIG RTN circuits at the temperature sensor harness connector.
Key on.
Access EOTV PID.
Is EOTV PID less than 0.3 volts?
Yes No
REPLACE suspect sensor. GO to DA117 . KEY OFF.
DA117 CHECK TEMPERATURE SENSOR SIGNAL AND SIG RTN CIRCUIT FOR OPEN IN HARNESS
Note: Refer to the PCM connector pins numbers on this pinpoint test cover page.
Disconnect PCM.
Measure resistance of EOT circuit between PCM harness connector pin and EOT sensor harness connector.
Measure resistance of SIG RTN circuit between PCM harness connector pin and EOT sensor harness connector.
Is each resistance less than 5.0 ohms?
Yes No
REPLACE PCM (refer to Section 2 , Flash EEPROM). REPAIR open circuits.
DA120 INTERMITTENT EOT SENSOR CHECK
Still monitoring PID, complete the following:
Tap on sensor to simulate road shock.
Wiggle the sensor connector.
Is there any large change in the PID reading?
Yes No
KEY OFF. DISCONNECT and INSPECT connector. If OK, REPLACE the sensor. GO to DA121 .
DA121 CHECK EOT ELECTRONIC ENGINE CONTROL (EC) WIRING HARNESS
Still monitoring PID, complete the following:
Wiggle, shake and bend small sections of wiring harness while working from the sensor to the PCM.
Is there any large change in the PID reading?
Yes No
ISOLATE fault. REPAIR as necessary. Fault is not present at this time. For Continuous Memory DTCs, COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles).
DA130 DTC P0298: ENGINE OIL OVER TEMPERATURE CONDITION
Engine oil temperature protection strategy in the PCM has been activated.
Check for overheating condition and base engine concerns.
Is there any overheating or base engine concerns?
Yes No
ISOLATE fault. REPAIR as necessary. REFER to Engine System - General Information, Section 303-00 in the Workshop Manual. GO to DA131 .
DA131 CHECK FOR EOT SENSOR HARDWARE
Engine oil temperature protection strategy in the PCM can be activated with or without an EOT sensor.
Does vehicle have an EOT sensor?
Yes No
GO to DA111 . IDENTIFY customer driving habits. Advise customer improper transmission gear selection and high rpm for extended period will initialize engine protection strategy.
