ATC Messages Not Received
NOTE:
After making any repairs, perform BODY VERIFICATION TEST
under VERIFICATION TESTS.
- Connect scan tool to Data Link Connector (DLC). Turn ignition on. Using scan tool, attempt to communicate with Body Control Module (BCM). If scan tool communicates with BCM, go to next step. If scan tool does not communicate with BCM, repair communication concern. See NO RESPONSE FROM BODY CONTROL MODULE (BUS +/- SIGNAL OPEN) .
- Turn ignition off. Remove and inspect fuse No. 17 (10-amp) in junction block. If fuse is blown, go to next step. If fuse is okay, go to step 5 .
- Measure resistance between ground and output cavity at fuse No. 17. If resistance is 5 ohms or less, go to next step. If resistance is greater than 5 ohms, replace fuse No. 17.
- Disconnect Automatic Temperature Control (ATC) head harness connector. Measure resistance between ground and terminal No. 10 (White wire) at ATC head harness connector. See Fig 1 . If resistance is greater than 5 ohms, replace fuse No. 17 and ATC head. If resistance is 5 ohms or less, replace fuse and repair short to ground in White wire between ATC head and fuse No. 17.
- Turn ignition on. Measure voltage at input side of fuse No. 17. If battery voltage exists, go to next step. If battery voltage does not exist, repair power distribution circuit as necessary. See POWER DISTRIBUTION article in WIRING DIAGRAMS.
- Turn ignition off. Install fuse No. 17. Disconnect Automatic Temperature Control (ATC) head harness connector. Turn ignition on. Measure voltage at terminal No. 10 (White wire) at ATC head harness connector. See Fig 1 . If battery voltage exists, go to next step. If battery voltage does not exist, repair open in White wire between ATC head and fuse No. 17.
- Turn ignition off. Measure resistance between ground and terminals No. 1 (Black/Light Green wire) and No. 3 (Black wire) at ATC head harness connector. If both resistances are 5 ohms or less, go to next step. If either resistance is greater than 5 ohms, repair open in appropriate wire between ground and ATC head.
- Connect Diagnostic Readout Box (DRBIII(R)) to Data Link Connector (DLC). Connect Scope Input Cable (CH7058) to channel one connector on DRBIII(R). Connect Red and Black leads and Cable Probe Adapter (CH7062) to scope input cable. Using DRBIII(R), access lab scope 12-volt square wave and set to 20-volt range. Go to next step.
- Connect Black lead to ground and Red lead to terminal No. 2 (Violet/Yellow wire) at ATC head harness connector. Turn ignition on. If voltage does not pulse from zero to 7.5 volts, go to next step. If voltage pluses from zero to 7.5 volts, replace ATC head.
- Turn ignition off. Disconnect Body Control Module (BCM) harness connector C1. Measure resistance in Violet/Yellow wire between terminal No. 2 at ATC head harness connector and terminal No. 4 at BCM harness connector C1. See Figure and Fig 1 . If resistance is 5 ohms or less, replace BCM. If resistance is greater than 5 ohms, repair open in Violet/Yellow wire between BCM and MHSMM.