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Incorrect Ambient Temperature Readings

NOTE: For connector terminal identification and wiring diagrams, see BODY CONTROL COMPUTER - INTRODUCTION article. Drive vehicle at least 3 miles (more than 25 MPH) to update CMTC. Perform VERIFICATION TEST VER-1A  after each repair.
NOTE: For CMTC wiring diagram, see ANALOG INSTRUMENT PANELS - FWD VANS 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. If resistance measurement does not correspond with specification, replace sensor. If sensor is within specification, 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. Turn ignition off. Close all vehicle doors and ensure all lights are off. Using scan tool in ohmmeter mode, measure resistance at ambient temperature sensor connector terminal No. 1 (Black/Light Blue wire). If resistance is less than 5 ohms, go to step  6 . If resistance is 5 ohms or more, go to next step.
  3. 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. If resistance measurement corresponds with specification, replace CMTC module. If reading does not correspond, go to next step.
  4. Disconnect ambient temperature sensor. Using scan tool in ohmmeter mode, measure resistance at ambient temperature sensor connector terminal No. 2 (Black/Light Blue wire). 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 more, repair Violet/Light Green wire for short to Black/Light Blue wire.
  5. Measure resistance at ambient temperature sensor connector terminal No. 1 (Violet/Light Green wire). 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 more, go to next step.
  6. Connect jumper wire between ground and ambient temperature sensor connector terminal No. 2 (Black/Light Blue wire). 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 more, repair open Black/Light Blue wire between CMTC module and ambient temperature sensor.
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