Diagnostic Test

1) VERIFY DTC U0020-CAN B BUS IS ACTIVE
Turn the ignition on.

With the scan tool, read Occupant Classification Module (OCM) DTCs.

Does the scan tool display active: U0019-CAN B BUS?

Yes
1. Go To 2).
No
1. If the DTC is stored, check for an intermittent condition by inspecting the related wiring harness for chafed, pierced, pinched, and partially broken wires. Also, inspect the related connectors for broken, bent, pushed out, spread, corroded, or contaminated terminals.
2. Perform AIRBAG SYSTEM VERIFICATION TEST - VER 1. Refer to *AIRBAG SYSTEM VERIFICATION TEST - VER 1 .
2) CHECK FOR ACTIVE CAN B BUS RELATED DTCS IN THE FRONT CONTROL MODULE (FCM)
With the scan tool, read Front Control Module (FCM) DTCs

Does the scan tool display any active CAN B BUS related DTCs?

Yes
1. Diagnose and repair the DTC(s).(Refer to ELECTRICAL/ELECTRONIC CONTROL MODULES - DIAGNOSIS AND TESTING) .
No
1. Go To 3).
3) CHECK (D55) CAN B BUS (+) CIRCUIT FOR AN OPEN

Fig 1: Measuring Resistance Between Front Control Module C1 Connector & OCM C1 Connector
Courtesy of DAIMLERCHRYSLER CORP.

Turn the ignition off.

Disconnect the negative battery cable.

WARNING: To avoid personal injury or death, turn the ignition off, disconnect the battery and wait two minutes before proceeding.

Disconnect the OCM connectors.

Disconnect the Front Control Module (FCM) C1 connector.

Measure the resistance of the (D55) CAN B Bus (+) circuit between the Front Control Module C1 connector and the OCM C1 connector.

Is the resistance below 2.0 ohms?

Yes
1. Go To 4).
No
1. Repair the (D55) CAN B Bus (+) circuit for an open.
2. Perform *OCCUPANT CLASSIFICATION MODULE SYSTEM VERIFICATION TEST. Refer to *OCCUPANT CLASSIFICATION MODULE SYSTEM VERIFICATION TEST .
4) CHECK (D54) CAN B BUS (-) CIRCUIT FOR AN OPEN

Fig 2: Measuring Resistance Between Front Control Module C1 Connector & OCM C1 Connector
Courtesy of DAIMLERCHRYSLER CORP.

Measure the resistance of the (D54) CAN B Bus (-) circuit between the Front Control Module C1 connector and the OCM C1 connector.

Is the resistance below 2.0 ohms?

Yes
1. Replace the OCM in accordance with the Service Information.
2. Perform *OCCUPANT CLASSIFICATION MODULE SYSTEM VERIFICATION TEST. Refer to *OCCUPANT CLASSIFICATION MODULE SYSTEM VERIFICATION TEST .
No
1. Repair the (D54) CAN B Bus (-) circuit for an open.
2. Perform *OCCUPANT CLASSIFICATION MODULE SYSTEM VERIFICATION TEST. Refer to *OCCUPANT CLASSIFICATION MODULE SYSTEM VERIFICATION TEST .