U0025

U0025-CAN B BUS (-) CIRCUIT LOW

U0025 - CAN B Bus (-) Circuit Low:

WHEN MONITORED
Continuously

SET CONDITION
The FCM detects the (D54) CAN B Bus (-) circuit is shorted to ground.

POSSIBLE CAUSES
- (D54) CAN B BUS (-) circuit shorted to ground or to (D55) CAN B BUS (+) circuit
- Any CAN B BUS module
- Front control module

Diagnostic Test

1. TEST FOR INTERMITTENT CONDITION

Turn the ignition on.
With the scan tool, record and erase FCM DTC's.
Cycle the ignition from on to off 3 times.
Turn the ignition on.
With the scan tool, read active FCM DTC's.

Q: Does the scan tool display this DTC as active?

YES: Go To 2
NO: The conditions that caused this code to set are not present at this time. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors.




2. CHECK THE (D54) CAN B BUS (-) CIRCUIT FOR A SHORT TO GROUND

Turn the ignition off.
Disconnect the Front Control Module C1 harness connector.
Measure the resistance between ground and the (D54) CAN B Bus (-) circuit.

Q: Is resistance below 1000.0 ohms?

YES: Go To 3
NO: Go To 4




3. (D54) CAN B BUS (-) CIRCUIT SHORTED TO GROUND

Measure the resistance between ground and the (D54) CAN B Bus (-) circuit.
While monitoring the ohmmeter, disconnect each CAN B Bus module one at a time.

NOTE:
- This is to determine if the short to ground is internal within a module or if the circuit is shorted.
- Disconnecting an in-line connector can eliminate a module or group of modules from the list of possible causes for this fault. Refer to the wiring diagrams to assist in diagnosis.

Q: Is resistance below 1000.0 ohms with all the CAN B Bus modules disconnected?

YES: Repair the (D54) CAN B Bus (-) circuit for a short to ground. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Replace the module that when disconnected the short to ground was eliminated,. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test




4. CHECK THE (D55) CAN B BUS (+) CIRCUIT FOR A SHORT TO THE (D54) CAN B BUS (-) CIRCUIT

Measure the resistance between the (D55) CAN B Bus (+) circuit and (D54) CAN B Bus (-) circuit.

Q: Is resistance below 1000.0 ohms?

YES: Go To 5
NO: Inspect the wiring and connectors for damage or shorted circuits. If ok, replace the Front Control Module. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test




5. (D55) CAN B BUS (+) CIRCUIT SHORTED TO THE (D54) CAN B BUS (-) CIRCUIT

Measure the resistance between the (D55) CAN B Bus (+) circuit and (D54) CAN B Bus (-) circuit.
While monitoring the ohmmeter, disconnect each CAN B Bus module one at a time.

NOTE:
- This is to determine if the short together is internal within a module or if the circuits are shorted together.
- Disconnecting an in-line connector can eliminate a module or group of modules from the list of possible causes for this fault. Refer to the wiring diagrams to assist in diagnosis.

Q: Is resistance below 1000.0 ohms with all the CAN B Bus modules disconnected?

YES: Repair the (D55) CAN B Bus (+) circuit for a short to the (D54) CAN B Bus (-) circuit. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test
NO: Replace the module that when disconnected the short to ground was eliminated,. Perform BODY VERIFICATION TEST - VER 1. Body Verification Test