P0573
Cruise Control/Brake Switch A Circuit Low
Powertrain Speed/Idle Control Cruise Control System 🟡 Moderate — Fix within a week
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What This Actually Means
In plain language — no jargon

Your car's cruise control brake switch is sending a weak electrical signal to the engine computer, like a dimly lit warning light instead of a bright one. The ECU can't properly detect when you press the brake pedal, which disables cruise control as a safety measure.

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Symptoms You May Notice
3 known symptoms for this code
Cruise control won't engage or suddenly disengages
Brake lights may not function properly
Check Engine Light illuminated
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Embedded Systems Insight
What the ECU/ECM is actually computing

The ECU monitors the voltage signal from the brake switch circuit, which should toggle between high (brake released) and low (brake pressed). When the voltage stays abnormally low or fails to reach the expected threshold, the ECU logs a fault. This protects against unintended cruise control operation when brakes are applied.

Voltage & Parameter Thresholds

Parameter Normal Range Fault Condition
Brake Switch Signal Voltage 4.5V - 5.0V (inactive); 0V - 0.5V (active) Voltage stuck below 0.8V or unable to switch properly
Circuit Resistance Less than 10 ohms when closed Greater than 50 ohms indicating corrosion or loose connection
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Diagnostic & DIY Fix Guide
Check these in order — from cheapest to most complex
1
Brake switch connector
Clean or reseat the connector at the brake pedal to remove corrosion and restore proper voltage signal.
2
Wiring harness
Inspect the cruise control brake switch wiring for damaged insulation, pinches, or loose connections between pedal and ECU.
3
Brake switch assembly
Replace the brake switch if voltage cannot be restored and connector/wiring are confirmed good.