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Test E - Coolant Temperature Sensor

NOTE: To pass this test, coolant temperature must be 50-240°F (10-116°C) for Key On-Engine Off Self-Test and 180-240°F (82-116°C) for Key On-Engine Running Self-Test.
  1. Code 21. Start engine and bring to normal operating temperature. Check that upper radiator hose is hot and pressurized. Perform QUICK TEST  s before continuing. If code 21 appears, go to next step. If no code 21, service other codes. If vehicle stalls, go to TEST X  .
  2. Turn ignition off and wait 10 seconds. Disconnect Engine Coolant Temperature (ECT) sensor and inspect connectors for damaged pins, corrosion and loose wires. Place DVOM on 20 volt scale. Turn ignition on. Measure voltage at ECT harness connector between coolant signal circuit and signal return circuit. If 4-6 volts, go to step  5 . If less than 4 volts, go to step  3 . If more than 6 volts, go to TEST C  .
  3. Turn ignition off and wait 10 seconds. With harness disconnected at ECT sensor, disconnect 60-pin connector at ECA. Inspect for damaged pins, corrosion and loose wires. Connect breakout box and leave ECA disconnected. With DVOM on 200 ohm scale, measure resistance of ECT harness connector between coolant signal circuit and box pin 7. Then measure resistance of connector between signal return circuit and box pin 46. If both readings are less than 5 ohms, go to step  4 . If either is 5 ohms or greater, repair open circuit. Remove breakout box, reconnect ECA and ECT sensor and repeat QUICK TEST  .
  4. Turn ignition off. Breakout box connected and ECA and ECT sensor disconnected. With DVOM on 200,000 ohm scale, measure resistance between box pin 7 and pins 40 and 60. If either reading is less than 10,000 ohms, service short circuit. Remove breakout box, reconnect ECA and ECT sensor and repeat QUICK TEST  . If both readings are 10,000 ohms or more, go to next step.
  5. Reconnect ECA and ECT sensor. Remove breakout box. Warm engine to normal operating temperature, turn ignition off and wait 10 seconds. Disconnect harness at ECT sensor. With DVOM on 200,000 ohm scale, measure resistance of ECT sensor. In KEY ON-ENGINE OFF (KOEO) SELF-TEST  , reading should be 1300-7700 ohms. In KEY ON-ENGINE RUNNING (KOER) SELF-TEST  , reading should be 1550-4550 ohms. If both are within limits, replace ECA, reconnect sensor and repeat QUICK TEST  . If not within limits, replace ECT sensor and repeat QUICK TEST  .
  6. Code 51. Turn ignition off and wait 10 seconds. Reconnect 60-pin connector at ECA and remove breakout box. Disconnect ECT sensor harness and inspect for damaged pins, corrosion and loose wires. Insert jumper wire in ECT sensor harness between coolant signal circuit and signal return circuit. Run KEY ON-ENGINE OFF (KOEO) SELF-TEST  . If code 61 appears, replace ECT sensor, remove jumper wire, reconnect harness and repeat QUICK TEST  . If no code 61, go to next step.
  7. Turn ignition off and wait 10 seconds. Remove jumper. Disconnect 60-pin connector at ECA and inspect for damaged pins, corrosion and loose wires. Connect breakout box, leaving ECA disconnected. With DVOM on 200 ohm scale, measure resistance of ECT harness between coolant signal circuit and box pin 7 and signal return circuit and box pin 46. If either is 5 ohms or more, repair open in harness, remove breakout box, reconnect ECA and ECT sensor and repeat QUICK TEST  . If both are less than 5 ohms, replace ECA, remove breakout, reconnect ECA and ECT sensor and repeat QUICK TEST  .
  8. Code 61. Turn ignition off and wait 10 seconds. Disconnect 60-pin connector at ECA and inspect for damaged pins, corrosion and loose wires. Perform KEY ON-ENGINE OFF (KOEO) SELF-TEST  . If code 51 appears, replace ECT and repeat QUICK TEST  . If no code 51, go to next step.
  9. Turn ignition off and wait 10 seconds. With ECT disconnected, install breakout box and leave ECA disconnected. With DVOM on 200,000 ohm scale, measure resistance between box pin 7 to pins 40 and 60. If any less than 10,000 ohms, repair short in harness and repeat QUICK TEST  . If both 10,000 ohms or more, replace ECA and repeat QUICK TEST  .
  10. Continuous Monitor Code 21. Turn ignition off and wait 10 seconds. Remove breakout box, reconnect ECA and ECT sensor and prepare vehicle for test drive (all test equipment removed). During test drive, try to simulate complaint and keep complaint active for at least 1 minute. After test drive, perform KEY ON-ENGINE OFF (KOEO) SELF-TEST  . If code 21 present, ensure thermostat is operating properly. If okay, replace ECT sensor and repeat QUICK TEST  . If no code 21, unable to duplicate fault at this time. Continuous Code 21 test complete.
  11. Continuous Monitor Codes 51 and 61. Enter CONTINUOUS MONITOR TEST  mode and observe volt/ohmmeter for fault indication while doing the following: Lightly tap on ECT sensor to simulate road shock. Wiggle sensor connector. If fault is indicated or voltage reading exceeds 5 volts, disconnect harness connectors at ECT and ECA. If connectors and terminals are okay, replace sensor and repeat QUICK TEST  . If no fault indicated, go to next step.
  12. Observe volt/ohmmeter while performing the following: Beginning at ECT, wiggle, shake or bend small sections of harness while working way to dash panel. Then repeating process from panel to ECA. If fault is indicated, isolate and repair problem and repeat QUICK TEST  . If no fault indicated, go to next step.
  13. Turn ignition off and wait 10 seconds. Disconnect 60-pin connector at ECA and inspect connector and terminals for damage. If damaged, service as required and repeat QUICK TEST  . If okay, fault cannot be duplicated at this time. Continuous Code 51 and 61 testing is complete.
Fig 1: Engine Coolant Temperature Sensor Circuits
G9339
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