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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  . Drive vehicle at least 3 miles (greater than 25 MPH) to update CMTC and perform, after each repair, VERIFICATION TEST VER-1A - VERIFICATION PROCEDURE  .
NOTE: For CMTC wiring diagram, see INSTRUMENT PANEL - ANALOG article.
CAUTION: Always turn ignition switch to OFF position prior to disconnecting any module connector.
  1. Disconnect and remove ambient temperature sensor. Sensor is located behind front bumper, right of center. Using external ohmmeter, measure resistance between sensor terminals and compare with AMBIENT TEMPERATURE SENSOR SPECIFICATIONS table. Go to next step.
    AMBIENT TEMPERATURE SENSOR SPECIFICATIONS

    Ambient Temperature k/ohms
    32°F (0°C) 29.3-36.0
    50°F (10°C) 18.0-22.0
    68°F (20°C) 11.4-13.6
    77°F (25°C) 9.1-10.8
    86°F (30°C) 7.4-8.7
    104°F (40°C) 4.9-5.7
    122°F (50°C) 3.3-3.8
  2. If resistance measurement does not correspond with AMBIENT TEMPERATURE SENSOR SPECIFICATIONS  table, replace sensor. If sensor is within specification, turn ignition off. Close all vehicle doors and ensure all lights are off. Wait one minute.
  3. Using scan tool in ohmmeter mode, measure resistance at terminal No. 1 (Black/Light Blue wire) on ambient temperature sensor connector. If resistance is less than 5 ohms, go to step 5). If resistance is 5 ohms or greater, go to next step.
  4. Connect jumper wire between ground and terminal No. 1 (Black/Light Blue wire) at sensor connector. Disconnect CMTC module connector. Using scan tool in ohmmeter mode, measure resistance at terminal No. 2 (Black/Light Blue wire) on CMTC module connector. If resistance is less than 5 ohms, replace CMTC module. If resistance is 5 ohms or greater, repair open Black/Light Blue wire between CMTC module and ambient temperature sensor.
  5. Connect ambient temperature sensor. Disconnect CMTC module connector. Using external ohmmeter, measure resistance between terminals No. 2 (Black/Light Blue wire) and No. 5 (Violet/Light Green wire) on harness connector. Compare ohmmeter reading with AMBIENT TEMPERATURE SENSOR SPECIFICATIONS  table. Go to next step.
  6. If resistance measurement corresponds with AMBIENT TEMPERATURE SENSOR SPECIFICATIONS  table, replace CMTC module. If reading does not correspond, disconnect ambient temperature sensor. Go to next step.
  7. Using scan tool in ohmmeter mode, measure resistance at terminal No. 1 (Black/Light Blue wire) on sensor connector. If resistance is less than 500 k/ohms, repair Black/Light Blue wire for partial short to ground. If resistance is 500 k/ohms or greater, go to next step.
  8. Move scan tool probe to terminal No. 2 (Violet/Light Green wire) on sensor connector. If resistance is less than 500 k/ohms, repair Violet/Light Green wire for partial short to ground. If resistance is 500 k/ohms or greater, repair Violet/Light Green wire for short to Black/Light Blue wire.
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