Bus +/- Signals Open Or No Response From Sentry Key Immobilizer Module

Possible Causes:

Attempt To Communicate With The BCM
Ground Circuit Open
Fused B+ Circuit Open
Open PCI Bus Circuit
Sentry Key Immobilizer Module

Testing

Turn the ignition on. With the DRBIII(R), enter Body then Body Computer. Was the DRBIII(R) able to I/D or communicate with the BCM? If yes go to next step. If no, refer to COMMUNICATION in DIAGNOSTIC TROUBLE CODE IDENTIFICATION or SYMPTOM IDENTIFICATION tables. Perform SENTRY KEY IMMOBILIZER SYSTEM VERIFICATION TEST (SKIS) .
Turn the ignition off. Disconnect the SKIM harness connector. Measure the resistance between ground and each ground circuit. Is the resistance below 5.0 ohms for both measurements? If yes, go to next step. If no, repair the ground circuit for an open. Perform SENTRY KEY IMMOBILIZER SYSTEM VERIFICATION TEST (SKIS) .
Turn the ignition off. Disconnect the SKIM harness connector. Using a 12-volt test light connected to ground, probe both Fused B+ circuits. Is the test light illuminated for bath circuits? If yes go to next step. If no, repair the Fused B+ circuit for an open. Perform SENTRY KEY IMMOBILIZER SYSTEM VERIFICATION TEST (SKIS) .

NOTE: Ensure there is PCI Bus Communication with other modules on the vehicle before proceeding. If not, diagnose and repair Communication problem as necessary. See COMMUNICATIONS in DIAGNOSTIC TROUBLE CODE IDENTIFICATION and SYMPTOM IDENTIFICATION tables.

Disconnect the Skim harness connector. Use Scope Input Cable (CH7058), Cable-to-Probe adapter CH-1062, and the red and black test probes. Connect the scope input cable to the channel one connector on the DRBIII(R). Attach the red and black leads and the cable to probe adapter to the scope input cable. With the DRBIII(R) 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 SKIM connector. Turn the ignition on. Observe the voltage display on the DRBIII(R) Lab Scope. Does the voltage pulse from 0 to approximately 7.5 volts? If yes, go to next step. If no, repair the PCI Bus circuit for an open. Perform SKIS VERIFICATION.
If there are no possible causes remaining, replace and program the SKIS. See ANTI-THEFT SYSTEMS - LIBERTY article. Perform SENTRY KEY IMMOBILIZER SYSTEM VERIFICATION TEST (SKIS) .