GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The engine control module (ECM) monitors the stop lamp switch signal circuit and the cruise control release signal circuit every 100 ms. The ECM monitors the status of the stop lamp switch signal circuit and the cruise control signal circuit to see if they match when the brake pedal is pressed or released.

Conditions for Running the DTC

The ignition is ON.

Conditions for Setting the DTC

The status of the stop lamp switch input to the ECM, and the cruise/brake switch input to the ECM do not match for at least 2 seconds continuously, for 10 occurrences. Each time the signals match then do not match at counter increments. When the counter reaches 10 the DTC will set.

Action Taken When the DTC Sets

When DTC P0504 is set the following will occur:

    • The cruise control is disabled.
    • The ECM will function as if the brake pedal is not pressed.
    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The malfunction indicator lamp (MIL) will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.

Conditions for Clearing the DTC

    • The DTC will clear when the status of the stop lamp switch input to the ECM, and the cruise/brake switch input to the ECM match for at least 2 seconds continuously for both the pressed position and the released position.
    • A current DTC Last Test Failed clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic.
    • Clear the DTC with a scan tool.

Diagnostic Aids

    • Inspect for proper adjustment of the stop lamp switch and cruise/brake switch. Refer to Cruise Release Switch Adjustment in Cruise Control and Stop Lamp Switch Adjustment .
    • Check for internments and poor connections. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Step

Action

Yes

No

Schematic Reference: Exterior Lights Schematics and Cruise Control Schematics in Cruise Control

Connector End View Reference: Master Electrical Component List in Wiring Systems

1

Did you perform the Diagnostic System Check - Lighting Systems?

Go to Step 2

Go to Diagnostic System Check - Lighting Systems

2

  1. With the scan tool, observe the Brake Switch parameter and the Cruise Brake Switch parameter.
  2. Press and release the brake pedal.

Does the Brake Switch parameter and the Cruise Brake Switch parameter display change closely with each other?

Go to Diagnostic Aids

Go to Step 3

3

  1. With the scan tool, observe the Cruise Brake Switch parameter.
  2. Press and release the brake pedal.

Does the Cruise Brake Switch parameter display change with the brake pedal position?

Go to Step 6

Go to Step 4

4

  1. Turn OFF the ignition.
  2. Disconnect the cruise/brake switch.
  3. Turn ON the ignition, with the engine OFF.

Does the Cruise Brake Switch parameter display Applied?

Go to Step 5

Go to Step 12

5

  1. Turn OFF the ignition.
  2. Connect a 10-amp fused jumper between the ignition positive voltage circuit of the cruise brake switch and the cruise control release signal circuit of the cruise brake switch.
  3. Turn ON the ignition, with the engine OFF.

Does the Cruise Brake Switch parameter display Released?

Go to Step 16

Go to Step 8

6

  1. Turn OFF the ignition.
  2. Disconnect the stop lamp switch.
  3. Turn ON the ignition, with the engine off.
  4. With the scan tool, observe the Brake Switch parameter.

Does the Brake Switch parameter display Released?

Go to Step 7

Go to Step 10

7

  1. Turn OFF the ignition.
  2. Connect a 15-amp fused jumper between the battery positive voltage circuit of the stop lamp switch and the stop lamp switch signal circuit.
  3. Turn ON the ignition, with the engine OFF.

Does the Brake Switch parameter display Applied?

Go to Step 15

Go to Step 11

8

Test the ignition positive voltage circuit of the cruise/brake switch for an open, high resistance, or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 9

9

Test for an open, high resistance, or short to ground in the cruise control release signal circuit of the cruise/brake switch. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 14

10

Test the stop lamp switch signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 14

11

Test the battery positive voltage circuit of the stop lamp switch for an open or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 13

12

Test the cruise control release signal circuit of the cruise/brake switch for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 17

13

Test the stop lamp switch signal circuit for an open, high resistance, or short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 14

14

Inspect for poor connections at the harness connector of the engine control module (ECM). Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 17

15

Inspect for poor connections at the harness connector of the cruise/brake switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 18

16

Inspect for poor connections at the harness connector of the stop lamp switch. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 20

Go to Step 19

17

Important: Program the replacement ECM.

Replace the ECM. Refer to Engine Control Module Replacement in Engine Controls - 3.0L (L81).

Did you complete the replacement?

Go to Step 20

--

18

Replace the stop lamp switch. Refer to Stop Lamp Switch Replacement .

Did you complete the replacement?

Go to Step 20

--

19

Replace the cruise/brake switch. Refer to Cruise Control Release Switch Replacement in Cruise Control.

Did you complete the replacement?

Go to Step 20

--

20

  1. Use the scan tool in order to clear the DTCs .
  2. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.

Does the DTC reset?

Go to Step 2

System OK