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For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 2007 🢒 Sierra Denali 🢒 Driver Information and Entertainment 🢒 Cellular, Entertainment, and Navigation 🢒 DTC P0703

Circuit Description

A mechanical switch attached to the brake pedal sends a signal to the transmission control module (TCM) indicating the service brake has been applied.

DTC P0703 is a type C DTC.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0703 Brake Switch Circuit

Conditions for Running the DTC
    • DTC P0721 and P0722 are not active.
    • The components are powered and ignition voltage is greater than 9.0 volts and less than 18 volts.

Conditions for Setting the DTC

DTC P0703 sets when the vehicle accelerates 10 times with the brake switch in the ON position, or decelerates 10 times with the brake switch in the OFF position.

Action Taken When the DTC Sets
    • The TCM does not illuminate the malfunction indicator lamp (MIL).
    • The TCM uses default assumption that the brake is OFF.
    • DTC P0703 is stored in TCM history.
    • The TCM inhibits torque converter clutch (TCC) engagement.
    • The TCM inhibits grade braking.

Conditions for Clearing the DTC

A scan tool can clear the code from TCM history. The TCM automatically clears the DTC from TCM history if the vehicle completes 40 warm-up cycles without failure.

Diagnostic Aids

DTC P0703 indicates that the TCM did not see the proper input signal for service brake status during an acceleration or deceleration cycle. This may indicate an open or short in the TCC brake switch/cruise control release circuit or a faulty stop lamp switch.

    • Inspect the wiring for poor electrical connections at the TCM. Inspect for the following conditions:
       - A bent terminal
       - A backed-out terminal
       - A damaged terminal
       - Poor terminal tension
       - A chafed wire
       - A broken wire inside the insulation
    • When diagnosing for an intermittent short or open, massage the wiring harness while watching the test equipment for a change.
    • You may have to drive the vehicle in order to experience a condition.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step tests brake switch status.

    2.

  2. This step tests for voltage at the TCM.

    3.

  3. This step tests for voltage before the stop lamp switch.

    4.

  4. This step tests for voltage after the stop lamp switch.

Step

Action

Value

Yes

No

Schematic Reference: Automatic Transmission Controls Schematics

1

Did you perform the Diagnostic System Check - Vehicle?

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Go to Step 2

Go to Diagnostic System Check - Vehicle

2

  1. Install the scan tool.
  2. Turn ON the ignition, with the engine OFF.

    3. Important: Before clearing the DTC, use the scan tool in order to record the Freeze Frame and Failure Records for reference. The Clear Info function will erase the data.

  3. Record the DTC Freeze Frame and Failure Records.
  4. Clear the DTC.

    5. Caution: When performing service on or near the SIR components or the SIR wiring, the SIR system must be disabled. Refer to SIR Disabling and Enabling . Failure to observe the correct procedure could cause deployment of the SIR components, personal injury, or unnecessary SIR system repairs.

  5. Apply and release the service brake.

Does the scan tool indicate that the brake switch is toggling off and on?

--

Go to Diagnostic Aids

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect the 80-way connector at the TCM.
  3. Install the J 39700 breakout box, the J-47275 breakout box adapter and the J 47275-1 magnetic overlay.
  4. Turn ON the ignition.
  5. Using the DMM, measure voltage at connector terminal 2 and ground.
  6. Apply and release the service brake.

Is voltage within the specified value?

Brakes applied: 0.0 V

Brakes released: 12.0 V

Go to Diagnostic Aids

Go to Step 4

4

Using the DMM, measure voltage at terminal C of the stop lamp switch and ground. Refer to Automatic Transmission Controls Schematics .

Is voltage within the specified value?

B+

Go to Step 5

Go to Step 6

5

Using the DMM, measure voltage at terminal D of the stop lamp switch.

Is voltage available?

B+

Go to Step 8

Go to Step 7

6
  1. Remove the brake fuse.
  2. Inspect the brake fuse for an open. Refer to General Electrical Diagnosis .

Did you find and correct the condition?

--

Go to Step 9

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7

Repair or replace the stop lamp switch. Refer to Stop Lamp Switch Replacement .

Did you complete the repair or replacement?

--

Go to Step 9

--

8

Inspect the engine wiring harness for an open or short to ground. Refer to Circuit Testing and Wiring Repairs .

Did you find and correct the condition?

--

Go to Step 9

--

9

Perform the following procedure in order to verify the repair:

  1. Clear the DTC.
  2. Using the scan tool, monitor the brake switch.
  3. Operate the vehicle under the Conditions for Setting the DTC.
  4. Select Specific DTC.
  5. Enter DTC P0703.

Has the test run and passed?

--

Go to Step 10

Go to Step 2

10

With the scan tool, observe the stored information, capture info, and DTC Info.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List - Vehicle

System OK