GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1999 🢒 Grand Prix 🢒 Body and Accessories 🢒 Lighting Systems 🢒 Diagnostic System Check - Body Control System

System Description

The body control module (BCM) diagnostic system check identifies conditions that are associated with the BCM. The following test is the starting point for any BCM concern or complaint. The test directs you to the next logical step in diagnosing the complaint.

The BCM is a reliable component and is not likely to cause the malfunction.

The following items cause most system complaints:

    • Faulty wiring
    • Faulty connectors
    • Faulty components

Understand the computer system and use the tables correctly in order to achieve the following results:

    • Reduce diagnostic time
    • Prevent unnecessary parts replacement

Diagnostic Aids

The following conditions may result in an intermittent operation of the BCM with no DTC stored:

    • Any condition which results in the interruption of power to the BCM
    • Out of range battery voltage specification. Normal battery voltage is 9-16 volts.
    • A loose or damaged ground(s).

It may be difficult to detect and accurately diagnose an intermittent failure in the electronic system. The BCM tests for the different malfunctions under different vehicle conditions. A test drive may cause a malfunction to repeat. If the system malfunction is not repeated during the test drive, a good description of the complaint may be useful in locating an intermittent fault condition.

Faulty electrical connections or wiring causes most intermittent problems. If you suspect an intermittent condition, inspect the suspected circuits for the following conditions:

    • Poor mating of the connector halves or backed out terminals
    • Improperly formed or damaged terminals
    • Wire chafing
    • Poor wire to terminal connections
    • Dirty or corroded terminals
    • Damage to the connector bodies

Use a J 35616-A for diagnostic procedures that require probing or testing a terminal. Use of the J 35616-A ensures the following results:

    • No damage occurs to the terminal.
    • The tool determines if contact tension is sufficient.

DTC P1626 will set in the powertrain control module (PCM) if the following conditions exist:

    • The ignition is in the RUN position.
    • The BCM is disconnected.

When the BCM diagnostics and repairs are completed, refer to Engine Controls for additional information on the PCM related DTCs.

Test Description

The number(s) below refer to the step number(s) on the diagnostic table.

  1. This step checks if the BCM identifies its BCM type.

    2.

  2. This step checks if vehicle has correct BCM type installed.

    3.

  3. This step checks for DTCs stored in BCM memory.

    4.

  4. This step checks for a short to ground in CKT 240.

    5.

  5. This step checks for a short to ground in CKT 1540.

    6.

  6. This step checks for a short to ground in CKT 39.

    7.

  7. This step checks for a short to ground in CKT 443.

    8.

  8. This step checks for an open in CKT 1550.

    9.

  9. This step checks for an open in CKT 240.

    10.

  10. This step checks for an open in CKT 1540.

    11.

  11. This step checks for an open in CKT 39.

    12.

  12. This step checks for a short to B+ in CKT 39.

    13.

  13. This step checks for an open in CKT 443.

    14.

  14. This step checks for a short to B+ in CKT 443.

    15.

  15. This step checks for a short to B+ in CKT 1445.

    16.

  16. This step checks for an open in CKT 1445.

Body Control Module (BCM) Diagnostic System Check

Step

Action

Value(s)

Yes

No

1

  1. Close all doors.
  2. Turn the ignition switch to the OFF position.
  3. Remove the MALL PGM fuse located in the fuse block.
  4. Turn the ignition switch to the ACC position.

When the BCM enters the feature customization mode, the BCM identifies its type by flashing the fasten belts indicator lamp (and sounding the chime) a number of times equal to the BCM type number.

Does the BCM identify its type number?

--

Go to Step 2

Go to Step 4

2

Refer to Body Control System Circuit Description for details on BCM types.

Does the BCM type match vehicle equipment/option content?

--

Go to Step 3

Go to Step 22

3

Within one second, turn the ignition switch from the ACC position to the OFF position, then back to the ACC position.

Upon cycling the ignition switch as described above, the BCM enters the diagnostic/programming mode. At this point, the BCM may flash (and chime) any Diagnostic Trouble Codes (DTCs) stored in memory (if any). DTC numbers range between 1-8. Refer to Body Control System Circuit Description for more information regarding DTCs.

Is the BCM displaying any DTCs?

--

Go to Step 23

Go to Step 4

4

Test the INT LAMP fuse.

Is the INT LAMP fuse open?

--

Go to Step 5

Go to Step 6

5

  1. Replace the INT LAMP fuse.
  2. Test the INT LAMP fuse again.

Is the INT LAMP fuse open again.

--

Go to Step 24

Go to Step 6

6

Test the PWR LOCK fuse.

Is the PWR LOCK fuse open?

--

Go to Step 7

Go to Step 8

7

  1. Replace the PWR LOCK fuse.
  2. Check the INT LAMP fuse again.

Is the PWR LOCK fuse open again?

--

Go to Step 25

Go to Step 8

8

Test the I/P-IGN fuse.

Is the I/P-IGN fuse open?

--

Go to Step 9

Go to Step 10

9

  1. Replace the I/P-IGN fuse.
  2. Turn the ignition switch to the RUN position.
  3. Test the I/P-IGN fuse again.

Is the I/P-IGN fuse open again?

--

Go to Step 26

Go to Step 10

10

Test the MALL fuse.

Is the MALL fuse open?

--

Go to Step 11

Go to Step 12

11

  1. Replace the MALL fuse.
  2. Turn the ignition switch to the RUN position.
  3. Test the MALL fuse again.

Is the MALL fuse open again?

--

Go to Step 27

Go to Step 12

12

  1. Turn the ignition switch to the OFF position.
  2. Disconnect the BCM connector C1.
  3. Use a test light in order to connect between B+ and the BCM harness connector C1 terminal D.

Is the test light on?

--

Go to Step 13

Go to Step 28

13

Use a test light in order to connect between the BCM harness connector C1 terminal G and ground.

Is the test light on?

--

Go to Step 14

Go to Step 29

14

Use a test light in order to connect between the BCM harness connector C1 terminal H and ground.

Is the test light on?

--

Go to Step 15

Go to Step 30

15

  1. Disconnect the BCM connector C2.
  2. Turn the ignition switch to the Run position.
  3. Use a test light in order to correct between the BCM harness connector C2 terminal C13 and ground.

Is the test light on?

--

Go to Step 16

Go to Step 31

16

  1. Leave test light connected (from step 15).
  2. Turn the ignition switch to the OFF position.

Is the test light off?

--

Go to Step 17

Go to Step 32

17

  1. Turn the ignition switch to the RUN position.
  2. Use a test light in order to connect between the BCM harness connector C2 terminal D4 and ground.

Is the test light on?

--

Go to Step 18

Go to Step 33

18

  1. Leave test light connected (from step 17).
  2. Turn the ignition switch to the OFF position.

Is the test light off?

--

Go to Step 19

Go to Step 34

19

  1. Remove the MALL PGM fuse.
  2. Turn the ignition switch to the ON position.
  3. Use a test light in order to connect between the BCM harness connector C2 terminal C9 and ground.

Is the test light off?

--

Go to Step 20

Go to Step 35

20

  1. Turn the ignition switch to the ON position.
  2. Leave the test light connected (from step 19).
  3. Reinstall the MALL PGM fuse.

Is the test light on?

--

Go to Step 21

Go to Step 36

21
  1. Turn the ignition switch to the OFF position.
  2. Reconnect BCM connectors C1 and C2.
  3. Close all doors.
  4. Remove the MALL PGM fuse.
  5. Turn the ignition switch to the ACC position.

Does the BCM identify its type number?

--

Go to Step 38

Go to Step 37

22

Replace the BCM with the correct BCM type, according to vehicle equipment content/options. Refer to Body Control Module Replacement .

Is the repair complete?

--

Go to Step 1

--

23

Refer to the corresponding DTC table in this section for further diagnosis and repair.

Is the action complete?

--

Go to Step 1

--

24

Repair short to ground in CKT 240.

Is the repair complete?

--

Go to Step 1

--

25

Repair short to ground in CKT 1540.

Is the repair complete?

--

Go to Step 1

--

26

Repair short to ground in CKT 39.

Is the repair complete?

--

Go to Step 1

--

27

Repair short to ground in CKT 443.

Is the repair complete?

--

Go to Step 1

--

28

Repair a poor connection or an open in CKT 1550.

Is the repair complete?

--

Go to Step 1

--

29

Repair a poor connection or an open in CKT 240.

Is the repair complete?

--

Go to Step 1

--

30

Repair a poor connection or an open in CKT 1540.

Is the repair complete?

--

Go to Step 1

--

31

Repair a poor connection or an open in CKT 39.

Is the repair complete?

--

Go to Step 1

--

32

Repair a short to voltage in CKT 39.

Is the repair complete?

--

Go to Step 1

--

33

Repair a poor connection or an open in CKT 443.

Is the repair complete?

--

Go to Step 1

--

34

Repair short to voltage in CKT 443.

Is the repair complete?

--

Go to Step 1

--

35

Repair short to voltage in CKT 1445.

Is the repair complete?

--

Go to Step 1

--

36

Repair a poor connection or an open in CKT 1445.

Is the repair complete?

--

Go to Step 1

--

37
  1. Inspect BCM connectors for poor terminal contact. Make repairs as needed.
  2. If the BCM connector terminal contact is OK, then replace the BCM. Refer to Body Control Module Replacement .

Is the repair complete?

--

Go to Step 1

--

38

Were you sent here from another diagnostic table?

--

Return to Diagnostic Table

System OK