Bus +/- Signals Open Or No Response From Automatic Temperature Control Module
NOTE:
This procedure applies to vehicles equipped with automatic A/C.
NOTE:
After making any repairs, perform BODY VERIFICATION TEST under VERIFICATION TESTS.
- Turn the ignition on. With the DRB, enter Body then Body Computer. If the DRB was able to I/D or communicate with the BCM, go to the next step. If the DRB was not able to I/D or communicate with the BCM, refer to the symptom list for problems related to no communication with the BCM. See DIAGNOSTIC TROUBLE CODE IDENTIFICATION table.
- Turn the ignition off. Disconnect the ATC C2 harness connector. See Fig 1. Using a 12-volt test light connected to 12 volts, probe the Ground circuit. If the test light illuminated, go to the next step. If the test light did not illuminate, repair the Ground circuit for an open.
- Turn the ignition off. Disconnect the ATC C2 harness connector. See Fig 1. Using a 12-volt test light connected to ground, probe the Fused B+ circuit. If the test light illuminated, go to the next step. If the test light did not illuminate, repair the Fused B+ circuit for an open or short.
- Turn the ignition off. Disconnect the ATC C2 harness connector. See Fig 1. Turn the ignition on. Using a 12-volt test light connected to ground, probe the Fused Ignition Switch Output circuit. If the test light illuminated, go to the next step. If the test light did not illuminate, repair the Fused Ignition Switch circuit for an open or short.
- Disconnect the ATC C2 harness connector. See Fig 1. Use Scope input cable CH7058, Cable to Probe adapter CH7062, and the Red and Black test probes. Connect the scope input cable to the channel one connector on the DRB. Attach the Red and Black leads and the cable to probe adapter to the scope input cable. With the DRBIII® select Pep Module Tools. Select lab scope. Select Live Data. Select 12 volt square wave. Press F2 for Scope. Press F2 and use the down arrow to set voltage range to 20 volts. Set Probe to x10. Press F2 again when complete. Connect the Black lead to the chassis ground. Connect the Red lead to the PCI Bus circuit in the ATC connector. Turn the ignition on. Observe the voltage display on the DRB Lab Scope. If the voltage pulses from 0 to approximately 7.5 volts, go to the next step. If the voltage does not pulse from 0 to approximately 7.5 volts, repair the PCI Bus circuit for an open.
- If there are no possible causes remaining, replace the Automatic Temperature Control Module. See A/C-HEATER CONTROL PANEL under REMOVAL & INSTALLATION.
NOTE:
Ensure there is PCI Bus communication with other modules on the vehicle before proceeding. If not, refer to the symptom list and repair as necessary. See DIAGNOSTIC TROUBLE CODE IDENTIFICATION table.