GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Century (China) (CNG) 🢒 Brakes 🢒 Antilock Brake System 🢒 DTC U1255 Serial Data Line Malfunction

Object Number: 502360 Size: MF

Circuit Description

The BCM receives a vehicle security powertrain status message from the Powertrain Control Module (PCM) through the Class 2 serial data link when turning the ignition switch on.

Conditions for Setting the DTC

The BCM sets DTC U1255 when the BCM does not receive a vehicle security powertrain status message from the PCM within one minute of turning ignition switch on.

Action Taken When the DTC Sets
    • The BCM stores DTC U1255 in memory.
    • The SERVICE VEHICLE SOON indicator lamp turns on.
    • The BCM sends a message to the instrument cluster to turn on the SECURITY indicator lamp through the Class 2 serial data link.

Conditions for Clearing the DTC
    • U1255 DTC status changes from current to history when the BCM receives the vehicle security powertrain status message from the PCM.
    • A history DTC will clear after 100 consecutive ignition cycles if the condition for the fault is no longer present.
    • Using a scan tool.

Diagnostic Aids
    • The following conditions may cause an intermittent malfunction to occur:
       - An intermittent open in circuit 1049 or 1037.
       - Poor connections at the BCM, PCM, or Splice Pack SP205.
       - The BCM is open internally.
    • The BCM may store DTC U1255 if certain diagnostics are performed between the Powertrain Control Module (PCM) and the Data Link Connector (DLC).
    • DTC P1626 will set in the Powertrain Control Module (PCM) when the ignition switch is on with the Body Control Module (BCM) disconnected. When BCM diagnostics and repairs are completed, refer to OBD System Check in Engine Controls for additional information on PCM related DTCs.

Test Description

The number below refers to the step number on the diagnostic table.

  1. This step determines whether the malfunction is intermittent or the BCM is faulty.

Step

Action

Value(s)

Yes

No

1

Was the Data Link Connector system check performed?

--

Go to Step 2

Go to Diagnostic System Check - Data Link Communications

2

Was the BCM diagnostic system check performed?

--

Go to Step 3

Go to Scan Tool Diagnostics in Body Control System

3

  1. Turn the ignition switch on.
  2. Clear BCM DTCs.
  3. Check for BCM current DTCs.

Does this BCM DTC reset?

--

Go to Step 4

Go to Step 5

4
  1. Replace the BCM. Refer to Body Control Module Replacement for more information.
  2. After replacing the BCM, perform the Setup New BCM procedure. Refer to Body Control Module (BCM) Programming/RPO Configuration for more information.

Is the repair complete?

--

Go to Step 6

--

5

The malfunction is not present at this time. Refer to Diagnostic Aids for additional information regarding this DTC.

--

--

--

6
  1. Turn the ignition switch off.
  2. Reinstall connectors/components removed.
  3. Turn the ignition switch on.
  4. Clear BCM DTCs. Refer to Clearing DTCs for more information.
  5. Check for BCM current DTCs. Refer to Diagnostic Trouble Code (DTC) Displaying for more information.

Are there any BCM current DTCs set?

--

Go to Diagnostic System Check - Body Control System

System OK