P0720
Torque Converter/Brake Switch B Circuit Low
Powertrain Transmission Control Torque converter brake 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your transmission's brake switch signal is too weak or missing, like a dimly lit brake light that the computer can't properly detect. This prevents the torque converter from operating correctly and may cause transmission shifting problems.

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Symptoms You May Notice
3 known symptoms for this code
Check engine light illuminated
Transmission slipping or delayed shifts
Torque converter not locking/unlocking properly
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECM monitors the brake switch input voltage to detect when brakes are applied, which signals when to release the torque converter lock. A low voltage reading below the expected threshold triggers this fault. The ECU expects a clean 5V signal when brakes are released and near 0V when applied.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Brake Switch Voltage 4.5V–5.0V (released) / 0V–0.5V (applied) Below 1.5V continuously or erratic transitions
Signal Resistance Less than 10 ohms when closed Greater than 50 ohms indicating poor contact
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Brake switch connector
Disconnect and reconnect the brake switch wiring harness to remove corrosion or poor contacts.
2
Brake switch wiring harness
Inspect the wires for damage, pinching, or corrosion and repair any visible issues with electrical tape or wire stripper/crimper.
3
Brake switch assembly
Replace the brake switch mounted on the brake pedal if voltage tests confirm an open or stuck switch.