OBD-II Diagnostic Trouble Code
P0573 — Brake Switch A Circuit High
P0573 means the brake switch A circuit voltage is high, typically from a switch stuck closed, misadjustment, or a short to power. The ECM may think the brake is always applied.
Severity 3/5
Truck-relevant
Service this week
Severity
Service this week
Brake Switch A Circuit High
Code
P0573
Category
Powertrain
Subsystem
Speed
Truck-relevant
Yes
What this means for truckers
P0573 (Brake Switch A High) — opposite of P0572.
Before you replace parts — try this first
P0573 on the Speed system is most often brake switch stuck or out of adjustment — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Brake lights stay on, cruise control will not engage, and some trucks limit throttle or disable features that require the brake released.
Common causes
- CommonBrake switch stuck or out of adjustment ($50–$250)
- OccasionalWiring shorted to power ($100–$300)
- OccasionalPedal not fully returning ($50–$200)
How to fix
Check that the pedal fully returns and the switch plunger is fully depressed
When to use: First step
Adjust or replace the switch
When to use: When brake lights stay on
Check wiring for a short to power
When to use: When a new switch does not fix it
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P0500 — Vehicle Speed Sensor Malfunction
- → P0501 — Vehicle Speed Sensor Range/Performance
- → P0502 — Vehicle Speed Sensor Low Input
- → P0503 — Vehicle Speed Sensor Intermittent/Erratic/High
- → P0506 — Idle Control System RPM Lower Than Expected
Frequently Asked Questions
Can I drive with code P0573?
P0573 is severity 3 — plan service within a few days. Performance is likely degraded already (you may feel reduced power, harsher shifts, or slightly worse fuel economy). Continuing to drive risks additional damage to adjacent components.
How much does it cost to fix P0573 on a commercial truck?
Total repair cost ranges $50–$300 depending on the root cause. The cheapest fix is usually the first one listed below — Brake switch stuck or out of adjustment — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P0573 fail a DOT inspection?
P0573 is generally not a direct DOT inspection fail item by itself. Inspectors focus on safety-critical systems (brakes, steering, tires, lights, hours-of-service). However, the check engine light alone can trigger additional inspection scrutiny. Best practice: fix the code and clear it before a planned inspection.
What's the difference between P0573 and related codes?
P0573 is closely related to: P0500 (Vehicle Speed Sensor Malfunction), P0501 (Vehicle Speed Sensor Range/Performance), P0502 (Vehicle Speed Sensor Low Input), P0503 (Vehicle Speed Sensor Intermittent/Erratic/High). These codes share the same subsystem (speed) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P0573 is set without the companions, the issue is more isolated.
How do I prevent P0573 from coming back after a repair?
For P0573 (Brake Switch A Circuit High), prevention centers on the speed system. Inspect wheel speed sensor wiring at PM (rodents love it). Keep ABS tone rings clean.