Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set.

1. Perform On-Board Diagnostic (OBD) System Check. See BASIC DIAGNOSTIC PROCEDURES article. Go to next step.
2. If any Engine Coolant Temperature (ECT) DTCs are set, see appropriate DTC test. If no DTCs are set, go to next step.
3. Allow engine to cool. Ensure coolant level is full. If coolant level is okay, go to next step. If coolant level is low, check cooling system for leaks. Repair as necessary. Retest system.
4. Start engine and let idle. Using scan tool select ENG COOL TEMP. If display increases to greater than 70°F (21°C) within 2 minutes, check for an intermittent problem. See DIAGNOSTIC AIDS . If display is not as specified, go to next step.
5. Check thermostat for proper operation. Replace thermostat if necessary. Retest system. If thermostat is okay, go to next step.
6. Using a thermometer, check temperature of water in radiator. Compare reading with display on scan tool. If readings are fairly close, check for sticking thermostat or incorrect thermostat application. Repair as necessary. If display readings are not close, go to next step.
7. Turn ignition off. Disconnect PCM harness connectors. Measure resistance between ECT sensor signal circuit (Blue/Red wire) and ECT sensor ground circuit (Green wire) at PCM harness connector. Compare resistance reading with coolant temperature. See ENGINE COOLANT TEMPERATURE (ECT) SENSOR RESISTANCE  table. If readings are as specified, replace PCM. Retest system. If readings are not as specified, go to next step.
   ENGINE COOLANT TEMPERATURE (ECT) SENSOR RESISTANCE
   
   

   Temperature °F (°C)	Ohms
   -40 (-40)	100,700
   -22 (-30)	52,700
   5 (-15)	21,450
   23 (-5)	12,300
   41 (5)	7280
   59 (15)	4450
   77 (25)	2796
   95 (35)	1802
   113 (45)	1188
   140 (60)	667
   176 (80)	332
   212 (100)	177

8. Check for high resistance in ECT sensor signal circuit (Blue/Red wire) or sensor ground circuit (Green wire). Check for poor connections at PCM and ECT sensor. Repair as necessary. If ECT sensor circuit is okay, replace ECT sensor. Retest system.