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Test 3A: No Response From Automatic Temperature Control (ATC) Module

NOTE: For connector terminal identification and wiring diagrams, see BODY CONTROL COMPUTER - INTRODUCTION article. Perform VERIFICATION TEST VER-1  after each repair.
CAUTION: Always turn ignition off prior to disconnecting any module connector.
  1. Ensure ignition is off. Remove and inspect fuse No. 17. If fuse is okay, go to step  4 . If fuse is open, go to next step.
  2. Using external ohmmeter, measure resistance between ground and fuse No. 17 (White wire). If resistance is 5 ohms or more, replace fuse No. 17. If resistance is less than 5 ohms, go to next step.
  3. Disconnect Automatic Temperature Control (ATC) head. Measure resistance between ground and ATC connector terminal No. 10 (White wire). If resistance is 5 ohms or more, replace fuse No. 17 and ATC head. If resistance is less than 5 ohms, replace fuse and repair short to ground in White wire between ATC head and fuse No. 17.
  4. Reinstall fuse No. 17. Turn ignition on. Using external voltmeter, measure voltage between ground and output side of fuse No. 17 (White wire). If voltage is 10 volts or less, repair open Black/Orange wire between ignition switch and junction block. If voltage is more than 10 volts, go to next step.
  5. Turn ignition off. Disconnect Automatic Temperature Control (ATC) head. Measure voltage between ground and ATC connector terminal No. 10 (White wire). If voltage is 10 volts or less, repair open White wire between fuse No. 17 and ATC head. If voltage is more than 10 volts, go to next step.
  6. Turn ignition off. Close all doors and ensure all courtesy lights are off. Using an external ohmmeter, measure resistance between ground and ATC connector terminals No. 1 (Black/Light Green wire) and terminal No. 3 (Black wire). If resistance in either circuit is 5 ohms or more, repair open Black/Light Green or Black wire. If resistance in both circuits is less than 5 ohms, go to next step.
  7. Measure voltage between ground and ATC connector terminal No. 2 (Violet/Yellow wire). Turn headlights on and observe voltmeter. If voltage does not modulate above .6 volt, repair open Violet/Yellow wire. If voltage modulates above .6 volt, replace ATC head.
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