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Torque Converter/Brake Switch B Circuit Malfunction

Jump to the fix

Severity

High

Can I keep driving?

Avoid extended driving; visit a service soon.

First step

A typical diagnostic sequence used by mechanics, provided here for educational reference only. Diagnostic work should be performed by a qualified mechanic with the appropriate tools and training. 1. Walk to the back of the car and have someone press the pedal while you watch the brake lights. No lights, flickering, or lights stuck on points straight at the switch or its wiring before you touch a scanner 2.

  • PPowertrain
  • 0Generic code
  • 7Transmission
  • 03Sequence number

What does it mean?

A brake switch mounted at the brake pedal provides a signal when the brake is depressed. It signals the control module (Computer), which could be the TCM (Transmission Control Module), BCM (body control module), or PCM (powertrain control module body control module (BCM) that the brake is applied or released, and the TCC (Torque Converter Clutch) should be released. The brake switch is also called a brake on/off (BOO) switch. These modules monitor the brake pedal position sensor.

When the brake pedal is applied, the control module detects a predetermined voltage signal and sends a serial data message to the engine control module (ECM) indicating the status of the stop lamps. The control module receives a signal from the brake or TCC switch (Brake/TCC switch are usually part of the same switch assembly) that tells it the driver has pressed the brake pedal.

This switch is normally closed and receives an ignition switch voltage through a fused circuit, so the control module sees ignition voltage unless the brake pedal is depressed. The control module has detected accelerations and decelerations with no brake switch change.

NOTE: Whenever diagnosing a 700 series DTC (Diagnostic Trouble Code) with a transmission, transfer case or other driveline components, check for diagnostic trouble codes (DTCs) under chassis and body systems, not just under “P” or powertrain/engine or emission control type codes. Module communications DTCs are “U” codes. These are most often found when looking for DTCs under chassis or body systems.

Chassis related codes are labeled “C” and body system related codes are labeled “B” codes and these can cause drivetrain issues if they affect a sensor that is also used by the heating and air conditioning system. Figure 1 Brake/TCC Switch Wiring Diagram The DTC P0703 diagnostic code will set when the brake pedal position (BPP) TCC (Torque Converter Clutch) switch signal is not received by the control module: BCM, PCM, TCM, ECM).

This is a high/low signal, the computer either receives a voltage signal or not.

Symptoms

Likely causes

How to fix it

Codes From the Same System

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This information follows the generic OBD-II definition and does not replace a vehicle-specific diagnosis. The severity rating is rule-based; an authorised diagnostic reading is required for a definitive answer.