On Board Diagnostics II PCED

1999 PCED On Board Diagnostics II

SECTION 5: Pinpoint Tests

DL: Cylinder Head Temperature (CHT) Sensor

DL: Introduction

DL1 DTC P1288 OR P1116: CHECK OPERATION OF CYLINDER HEAD TEMPERATURE SENSOR

Run engine at 2000 rpm until engine temperature becomes stabilized.
No Starts :

GO to DL3 .

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 P1288 or P1116 present?

Yes	No
GO to DL2 .	Engine temperature was not stabilized. REPAIR any other DTCs as necessary.

DL2 CHECK VREF CIRCUIT VOLTAGE AT TP SENSOR

Refer to schematic at the beginning of this 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 DL3 .	GO to Pinpoint Test Step C1 .

DL3 CHECK RESISTANCE OF CYLINDER HEAD TEMPERATURE SENSOR WITH ENGINE OFF

Disconnect CHT sensor.
Measure resistance between CHT signal and SIG RTN pins at the CHT sensor. Refer to the table at the beginning of this pinpoint test for resistance specifications.

Is resistance within specification?

Yes	No
GO to DL4 .	REPLACE CHT sensor.

DL4 CHECK RESISTANCE OF CHT SENSOR WITH ENGINE RUNNING

Note: Verify that engine is at operating temperature before taking CHT readings.

Run engine for two minutes at 2000 rpm.
Measure resistance between CHT signal and SIG RTN pins at the CHT sensor. Refer to the table at the beginning of this Pinpoint Test for resistance specifications.
Key off.

Is resistance within specification?

Yes	No
REPLACE PCM (refer to Section 2 , Flash EEPROM).	REPLACE CHT sensor.

DL5 DTC P1289 OR P1290: ACCESS CHT PID AND CHECK VOLTAGE

Connect scan tool.
Key on, engine off.
Access CHT V PID.

Is the CHT V PID less than 0.2 volt?

Yes	No
GO to DL6 .	GO to DL7 .

DL6 CHECK FOR GROUNDED CIRCUIT

Disconnect CHT sensor.
Key on.
Access CHT V PID.

Is the CHT V PID more than 4.6 volts?

Yes	No
REPLACE CHT sensor.	GO to DL21 .

DL7 CHECK FOR OPEN HARNESS

Disconnect CHT sensor.
Connect a jumper wire between the CHT signal and SIG RTN circuits at the CHT sensor vehicle harness connector.
Key on.

Note: If a Scan Tool communication concern exists, remove jumper wire immediately and go to DL12 .

Access CHT V PID.

Is the CHT V PID less than 0.2 volt?

Yes	No
REPLACE CHT sensor.	REMOVE jumper wire. GO to DL11 . KEY OFF.

DL10 DTC P0118: SIMULATE OPPOSITE SIGNAL TO PCM

Disconnect CHT sensor.
Connect a jumper wire between the CHT signal circuit and SIG RTN circuit at the CHT sensor vehicle harness connector.
Connect scan tool.
Key on.

Note: If a Scan Tool communication concern exists, remove jumper wire immediately and go to DL12 .

Access CHT V PID.

Is the CHT V PID less than 0.2 volt?

Yes	No
REPLACE CHT sensor.	REMOVE jumper wire. GO to DL11 .

DL11 CHECK CHT SENSOR SIGNAL AND SIG RTN CIRCUITS FOR OPEN IN HARNESS

Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.

Disconnect PCM.
Measure resistance of CHT circuit between PCM harness connector pin and CHT sensor harness connector.
Measure resistance of SIG RTN circuit between PCM harness connector pin and CHT sensor harness connector.

Is each resistance less than 5.0 ohms?

Yes	No
REPLACE PCM (refer to Section 2 , Flash EEPROM).	REPAIR open circuits.

DL12 CHECK CHT SENSOR SIGNAL FOR SHORT TO VREF IN HARNESS

Key off.
Disconnect PCM.
Measure resistance between CHT and VREF circuits at the PCM harness connector.

Is resistance greater than 10,000 ohms?

Yes	No
REPLACE PCM (refer to Section 2 , Flash EEPROM).	REPAIR short to VREF.

DL20 DTC P0117: SIMULATE OPPOSITE SIGNAL TO PCM

Disconnect CHT sensor.
Connect scan tool.
Key on.
Access CHT V PID.

Is the CHT V PID more than 4.6 volts?

Yes	No
REPLACE CHT sensor.	GO to DL21 .

DL21 CHECK VREF CIRCUIT VOLTAGE AT TP SENSOR

Refer to schematic at the beginning of this Pinpoint Test.
Disconnect TP sensor.
Key on, engine off.
Measure 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 DL22 . KEY OFF.	GO to Pinpoint Test Step C1 .

DL22 CHECK CHT SIGNAL CIRCUIT FOR SHORT TO GROUND

Note: Refer to the PCM connector pin numbers in the beginning of this pinpoint test.

Disconnect PCM.
Measure resistance between CHT signal and SIG RTN circuits and then between CHT 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.

DL30 DTC P1285: EARLY WARNING OF ENGINE OVERHEAT CONDITION

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 symptom, Engine Overheats.	GO to Engine Cooling, Section 303-03 in the Workshop Manual for symptom, Loss of Engine Coolant.

DL40 ENGINE TEMPERATURE WARNING INDICATOR LAMP ALWAYS ON, ENGINE IS NOT OVERHEATING

Note: PCM Quick Test must be performed prior to entering this Pinpoint Test.

Was PCM Quick Test performed prior to entering this Pinpoint Test?

Yes	No
No Diagnostic Trouble Codes (DTCs) received during PCM Quick Test. GO to DL41 .	GO to Section 3 and RERUN Quick Test. REPAIR any DTCs as necessary.

DL41 ENGINE TEMPERATURE INDICATOR LAMP ALWAYS ON AND NO DIAGNOSTIC TROUBLE CODE (DTC)

The Engine Temperature Warning Indicator is an early warning of an engine overheating condition. The PCM monitors the cylinder head temperature (CHT) sensor and grounds Circuit 39 when the engine is beginning to overheat. This causes the indicator to illuminate and forces the temperature gauge to H (hot) zone. A DTC P1285 will also be stored in the PCM.

This test diagnoses Engine Temperature Warning Lamp ON/temperature gauge is in the H (hot) zone with no PCM DTCs.

Possible causes:

Damaged PCM.
Damaged engine coolant temperature sensor.
Instrument cluster concern.
Wiring harness fault, Circuit 39.

Disconnect PCM.
Key on.

Is the engine temperature warning indicator light OFF and the temperature gauge in the normal zone with the PCM disconnected?

Yes	No
Key off. REPLACE the PCM (refer to Section 2 , Flash EEPROM).	The PCM has not attempted to ground Circuit 39 and turn the engine temperature indicator light ON. GO to Instrument Cluster, Section 413-01 in the Workshop Manual.

DL90 DTCS P0117, P0118, P1117, P1289 OR P1290: INTERMITTENT CHECK

Connect scan tool.
Key on.
Monitor the CHT 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 temperature reading?

Yes	No
Key off. DISCONNECT and INSPECT connectors. If OK, REPLACE CHT sensor. COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles).	GO to DL91 .

DL91 CHECK ELECTRONIC ENGINE CONTROL (EC) WIRING HARNESS

Still monitoring PID.
While observing the appropriate PID, complete the following:

Hold the vehicle 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 temperature reading?

Yes	No
ISOLATE fault. REPAIR as necessary. COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles).	GO to DL92 .

DL92 CHECK PCM AND VEHICLE HARNESS CONNECTOR

Disconnect PCM.
Disconnect CHT sensor.

Are connectors and terminals OK?

Yes	No
Fault is not present at this time. COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles).	REPAIR as necessary. COMPLETE Comprehensive Component Monitor Repair Verification Drive Cycle (REFER to Section 2 , Drive Cycles).

DL100 DTC P1299 or P0217 INDICATES AN ENGINE OVERHEAT CONDITION OCCURRED

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 symptom, Engine Overheats.	GO to Engine Cooling, Section 303-03 in the Workshop Manual for symptom, Loss of Engine Coolant.