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Home / DTC / P0719 — Torque Converter/Brake Switch B Circuit Low

P0719 — Torque Converter/Brake Switch B Circuit Low

Detailed page for trouble code P0719.

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Code

P0719

MERCEDES-BENZ P — Powertrain

Torque Converter/Brake Switch B Circuit Low

Brand: MERCEDES-BENZ
Type: P — Powertrain
AI status
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Page language: EN

Causes

  • Open circuit in Brake Switch B wiring
  • Short to ground on Brake Switch B circuit
  • Corroded/loose connector or pin at switch or ECU
  • Failed brake switch (switch stuck or internal short)
  • Blown fuse or poor power/ground supply to switch circuit
  • Water intrusion or damaged wiring harness

Symptoms

  • MIL/CEL illuminated; diagnostic trouble code stored
  • Brake lights may be inoperative or stuck ON
  • Torque converter may not unlock properly or lockup may be disabled
  • Transmission may enter limp/backup mode or show erratic shifting
  • Cruise control or traction control may be disabled or behave unpredictably
  • Possible difficulty starting (if linked to brake switch function for start inhibit)

What to check

  • Retrieve freeze-frame data and all stored/transient codes with a scan tool
  • Check brake light operation at the lamps while pressing pedal
  • Visually inspect wiring and connectors for damage, corrosion, or water ingress from switch to transmission control module
  • Perform wiggle test on harness while monitoring live data for Brake Switch B signal
  • Measure voltage at brake switch connector with multimeter (key ON, engine OFF) and while actuating switch
  • Check for proper fuse(s) and any relays feeding the brake switch circuit

Signal parameters

  • Expected open-circuit voltage (switch released): ~battery voltage (≈11–14 V) — vehicle dependent
  • Expected closed-circuit voltage (switch actuated): near 0 V or ground reference (≤1 V) — vehicle dependent
  • ‘Low’ fault present when ECU sees sustained low voltage on Brake Switch B input when it expects high (or vice versa depending on vehicle wiring)
  • Typical continuity: closed switch ≈0–5 ohms; open switch ≈infinite (open)

Diagnostic algorithm

  1. Read and record DTCs and freeze-frame data; clear codes and attempt to reproduce
  2. Verify brake lamp operation. If brake lamps do not illuminate, focus on brake switch and power supply circuit
  3. Visually inspect switch, connector, and harness from pedal to ECU for obvious damage or corrosion; repair any physical faults
  4. With a digital multimeter: verify reference power (12 V) and ground at the brake switch connector with key ON; verify voltage changes when pedal is depressed
  5. Check continuity between brake switch B terminal and the ECU input pin; repair any opens
  6. If wiring checks are good, bench-test or replace the brake switch and retest the circuit
  7. If fault remains after wiring and switch replacement, inspect/repair connectors at ECU and retest; consider ECU input fault only after verifying wiring and switch integrity
  8. Clear codes and perform road test or reproduce conditions while monitoring live data to confirm repair

Likely causes

  • Damaged/chafed wiring between brake switch and ECU causing short to ground
  • Faulty or misadjusted brake light/brake pedal switch B
  • Corroded connector at switch or ECU terminal causing low voltage reading
  • Blown fuse or missing 12 V supply to the switch
  • Internal switch failure (contacts stuck closed or shorted)

Fault status

⚠️ Status
Control module reports a low-voltage condition on the Torque Converter / Brake Switch B circuit. This can prevent proper torque converter lockup and may affect transmission and vehicle functions. Inspect switch, wiring, fuses, and connectors before considering module replacement.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0700 P0705 P0715 P0720 P0504
856

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