P0573 - Cruise Control/Brake Switch A Circuit High
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System
Powertrain (Engine & Gearbox)
Related Fault Codes
Technical Description
The diagnostic trouble code (DTC) P0573 is triggered when the Engine Control Module (ECM) detects an abnormally high voltage signal from the Brake Switch 'A' circuit. This switch is a dual-purpose component used to illuminate brake lights and signal the ECM to disengage the Cruise Control system. A 'Circuit High' condition typically indicates that the signal voltage remains at a logic high level (often B+) due to a short to voltage, an open circuit in the ground path, or a faulty switch. The ECM monitors this circuit to ensure safe operation; if the signal is inconsistent or out of range, the Cruise Control system will be disabled as a safety precaution.
Possible Causes
Faulty brake light switch (internal short or mechanical failure)
Damaged wiring harness (Short to B+ or open ground circuit)
Incorrect brake light bulbs (e.g., LED conversion causing resistance issues)
Failed Engine Control Module (ECM) or issues with trailer wiring/connectors
Symptoms
Recommended Solution
Workflow
Mechanic's Tip
Before replacing expensive components, always double-check wiring and connections. 80% of all sensor faults are actually due to corroded contacts or broken wires.
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