P0704
Torque Converter/Brake Switch B Circuit Malfunction
Powertrain Transmission Control Torque Converter Control 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

The ECU detected a problem with the brake switch circuit that tells the transmission when to lock or unlock the torque converter. Think of it like a communication line between your brake pedal and transmission—if that line is broken or sending bad signals, the transmission gets confused about when to engage.

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

The ECU monitors the brake switch circuit voltage to determine brake pedal status, which signals whether the torque converter should lock for efficiency or unlock for smooth operation. The circuit should toggle between high and low voltage states when brakes are applied and released. If voltage remains stuck, fluctuates erratically, or fails to respond to brake input, the ECU logs a fault.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Brake Switch Voltage (Park/Neutral) 0V or 12V (stable, state-dependent) Floating voltage, no transition, or stuck high/low
Circuit Continuity >10 kΩ or <1 kΩ (depending on state) Open circuit or short to ground
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Brake switch connector
Clean and reseat the brake switch connector at the pedal assembly to eliminate corrosion or loose contact.
2
Brake switch
Replace the brake switch if it remains stuck in one position or fails continuity testing with a multimeter.
3
Wiring harness (brake switch circuit)
Inspect and repair any damaged, pinched, or corroded wiring between the brake switch and transmission control module.