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CMTC Test 4A - Incorrect Ambient Temperature Reading

NOTE: Perform CMTC TEST 1A  before proceeding with this test. For connector terminal identification, refer to CONNECTOR IDENTIFICATION  . For wiring diagrams, refer to WIRING DIAGRAMS  . After each repair, perform TEST VER-1A  .
CAUTION: Always turn ignition switch to OFF position prior to disconnecting any module connector. Ensure all connectors are clean and tight.
  1. Disconnect and remove ambient temperature sensor. See Figure under CMTC TEST 2A. Using an ohmmeter, measure ambient temperature sensor resistance. Compare reading with AMBIENT TEMPERATURE SENSOR RESISTANCE VALUES  table.
    NOTE: After repairing temperature reading problem, drive vehicle at least 3 miles at a steady speed above 25 MPH to update CMTC computer display.
  2. If ambient temperature sensor is not within specified resistance values, replace ambient temperature sensor. If ambient temperature sensor is within specified resistance values, go to next step.
  3. Turn ignition off. Close all doors. Turn all lights and accessories off. Using scan tool in ohmmeter mode, measure resistance at terminal No. 1 (Light Green/White wire) on ambient temperature sensor connector. If resistance is less than 5 ohms, go to step 6). If resistance is 5 ohms or more, go to next step.
  4. Connect jumper wire between ground and terminal No. 1 (Light Green/White wire) on ambient temperature sensor harness connector. Disconnect Body Control Module (BCM) Black 24-pin connector. BCM is located under left side of dash. See Figure in CHIME TEST 3A.
  5. Using scan tool in ohmmeter mode, measure resistance at terminal No. 2 (Light Green/White wire) on BCM Black 24-pin connector. If resistance is 5 ohms or more, repair open Light Green/White wire. If resistance is less than 5 ohms, replace BCM.
  6. Reconnect ambient temperature sensor. Disconnect BCM Black 24-pin connector. Using an ohmmeter, measure resistance between terminals No. 2 (Light Green/White wire) and No. 5 (Dark Green/Red wire) on BCM Black 24-pin connector. Compare reading with AMBIENT TEMPERATURE SENSOR RESISTANCE VALUES  table.
  7. If ambient temperature sensor is within specified resistance values, replace BCM. If ambient temperature sensor is not within specified resistance values, go to next step.
  8. Disconnect ambient temperature sensor connector. Using scan tool in ohmmeter mode, measure resistance at terminal No. 1 (Light Green/White wire) on ambient temperature sensor connector. If resistance is less than 500,000 ohms, repair short in Light Green/White wire. If resistance is 500,000 ohms or more, go to next step.
  9. Using scan tool in ohmmeter mode, measure resistance at terminal No. 2 (Dark Green/Red wire) on ambient temperature sensor connector. If resistance is less than 500,000 ohms, repair short in Dark Green/Red wire. If resistance is 500,000 ohms or more, repair short between ambient temperature sensor Dark Green/Red wire and Light Green/White wire.
AMBIENT TEMPERATURE SENSOR RESISTANCE VALUES

°F (°C) Ohms
32 29,300-36,000
50 18,000-22,000
68 11,400-13,600
77 9100-10,800
86 7400-8700
104 4900-5700
122 3300-3800
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