P0703 Brake Switch 2 Performance

P0703 code - The Powertrain Control Module (PCM) monitors the vehicle braking using the stop/brake lamp switch. For accuracy, the PCM monitors two separate brake switch signals. The operating mode of these signals are as follows:

P0703


Brake signal 1 operation: the PCM sends out a 12 volt , low amperage signal, which may not illuminate a test light, on the brake signal 1 circuit. The PCM monitors the voltage on this circuit to indicate if the brake pedal is depressed or released. The brake signal 1 signal is nomally closed through the stop/brake lamp switch. When the brake pedal is released, the brake signal 1 circuit is connected to the ground circuit and the PCM reads 0.0 volts on the brake signal 1 circuit. When the pedal is pressed, the path to ground is opened and the PCM reads 12 volts on the brake signal 1 circuit.

Brake signal 2 operation: 12 volts are sent on the ignition switch start/run circuit through the stop/brake lamp switch to the PCM on the brake signal 2 circuit. The PCM monitors the voltage on this circuit to indicate if the brake pedal is depressed or released. No voltage on the brake signal 2 circuit indicates to the PCM that the pedal is depressed, and 12.0 volts indicate that the brake pedal is released.

The Powertrain Control Module (PCM) determines the primary and secondary brake switch signals are not plausible.

Possible causes P0703 code

- Brake switch 1 signal circuit shorted to ground
- Brake switch 1 signal circuit open
- Ground circuit open
- Ignition switch start/run circuit open
- Brake switch 2 signal circuit shorted to voltage
- Brake switch 2 signal circuit open
- Stop lamp switch
- Powertrain Control Module (PCM)

Diagnostic test P0703 code

Step 1. Check the brake switch 1 status
Turn the ignition on, while observing the brake switch 1 status on the scan tool display, press and release the brake pedal several times.

Does the scan tool display brake switch 1:pressed and not pressed for the appropriate pedal position?

Yes, go to step 2.
No, go to step 8.

Step 2. Check the brake switch 2 status
While observing the brake switch 2 status on the scan tool display, press and release the brake pedal several times.

Does the scan tool display brake switch 2: pressed and not pressed for the appropriate pedal position?

Yes, go to step 3.
No, go to step 4.

Step 3. Intermittent condition
The conditions that set the DTC are not present at this time. The following list may help in identifying the intermittent condition. With the engine running at normal operating temparature, monitor the scan tool parameters related to the DTC while wiggling the wiring harness. Look for parameter valuee to change and/or a DTC to set. Review the DTC when monitored and set condition. If possible, try to duplicate the conditions under which the DTC was set. Perform any technical service bulletins that may apply. Visually inspect the related wiring harness. Look for aby chafed, pierced, pinched, or partially broken wires. Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.

Were any of the above conditions present?

Yes, repair as necessary.
No, test complete.

Step 4. Check the ignition switch start/run circuit for an open
Turn the ignition off, disconnect the brake lamp switch harness connector. Turn the ignition on , using a 12-volt test light connected to ground, probe the ignition switch start/run circuit at the brake lamp switch harness connector. The test light should be illuminated and bright.

Is the test light illuminated and bright?

Yes, go to step 5.
No, repair the ignition switch start/run circuit for an open.

Step 5. Check the brake switch 2 signal circuit for a short to voltage
Measure the voltage on the brake switch signal 2 circuit at the stop lamp switch harness connector.

Is there any voltage present?

Yes, repair the brake switch 2 signal circuit for a short to voltage.
No, go to step 6.

Step 6. Check the Brake switch 2 signal circuit for an open/high resistance
Turn the ignition off, disconnect the PCM harness connector. Measure the resistance of the brake switch 2 signal circuit between the brake lamp switch harness connector and the PCM harness connector.

Is the resistance below 2.0 Ohms?

Yes, go to step 7.
No, repair the brake switch 2 signal circuit for an open or high resistance.

Step 7. Check the brake lamp switch
Measure the resistance between terminal 3 and terminal 4 at the stop lamp switch harness connector with the brake pedal NOT depressed.

Is the resistance below 2.0 Ohms?

Yes, replace and program the Powertrain Control Module (PCM). Perform the Powertrain Verification Test.
No, replace the brake lamp switch.

Step 8. Check the ground circuit for an open/high resistance
Turn the ignition off, disconnect the brake lamp switch harness connector. Measure the resistance between ground and the ground circuit at the brake lamp switch harness connector.

Is the resistance below 5.0 Ohms?

Yes, go to step 9.
No, repair the ground circuit for an open or high resistance.

Step 9.  Check the brake switch 1 signal circuit voltage
Turn the ignition on, measure the voltage on the brake switch signal 1 circuit at the brake lamp switch harness connector.

Is the voltage reading approximately 12.0 volts?

Yes, replace the brake lamp switch.
No, go to step 10.

Step 10. Check the brake switch 1 signal circuit for a short to ground
Turn the ignition off, disconnect the PCM harness connector. Measure the resistance between ground and the brake switch 1 signal circuit at the brake lamp switch harness connector.

Is the resistance above 10k Ohms?

Yes, go to step 11.
No, repair the brake switch 1 signal circuit for a short to ground.

Step 11. Check the brake switch 1 signal circuit for an open/high resistance
Measure the resistance of the brake switch 1 signal circuit between the brake lamp switch harness connector and the PCM harness connector.

Is the resistance below 5.0 Ohms?

Yes, replace the Powertrain Control Module (PCM). Perform the Powertrain Verification Test.
No, repair the brake switch 1 signal circuit for an open or high resistance.

Test complete.

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