OBD-II trouble code
P0573: Cruise Control / Brake Switch "A" Circuit High
The module has never once seen you press the brake. Check the brake lamp fuse before you touch the switch — on many vehicles a single blown fuse produces this exact code and costs a dollar to fix.
Quick facts
- System
- Powertrain
- Category
- Cruise Control
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $1 – $420
- DIY difficulty
- Intermediate DIY
What does P0573 mean?
P0573 reports that the brake switch "A" circuit sat at the high end of its range and stayed there. Functionally, on most designs, that means the module has never observed a brake application. Not a weak one, not an intermittent one — none at all. Whatever the driver's foot is actually doing, the information is not arriving.
High readings on a switched input have a strong tendency to be opens rather than shorts to power, and that is worth internalising before you start testing, because the word "high" pulls people towards looking for stray voltage. Broken wires, backed-out terminals, unseated connectors and switches that have wound themselves out of adjustment all produce this. Actual shorts to a battery feed exist but they are the minority.
The cheapest cause is also the most overlooked, and it is the reason this page leads with it. On many vehicles the brake switch is powered from its own permanently live fuse, chosen so the brake lamps work whether or not the ignition is on. If that fuse opens, the switch is still perfect, the wiring is still perfect, and there is simply no voltage to switch — which the module reads as a circuit that never changes. A dollar fuse produces a code that looks exactly like a failed part. Anyone who checks the switch first and the fuse afterwards has done the expensive step before the free one.
What separates this code from its low sibling is the consequence set, and it is the reason this one deserves more urgency than a cruise control code normally would. A brake signal that never asserts takes a number of things with it. Cruise control will not engage, because the module cannot confirm the path that stops it. The brake-shift interlock may hold the shifter in park, which is what usually brings the vehicle in — the customer's complaint is that the car will not go into gear, and cruise control never enters the conversation. On push-button vehicles the start logic may refuse for the same reason. And if the open is upstream of the lamp contacts, the brake lights are dark, which every other vehicle on the road relies on.
That last point is why this code is worth treating as more than an inconvenience. Nothing about the car's own braking has changed — the hydraulics are entirely mechanical and completely unaffected — but the vehicle has lost its ability to tell anyone behind it that it is slowing down. That is a risk carried by other drivers rather than by the person holding the scan tool, and it is the argument for fixing this promptly even though the car drives perfectly well.
Common causes
- Blown brake lamp fuse, removing the feed the switch is supposed to switch
- Open circuit between the brake switch and the module
- Brake switch backed out on its mount so the plunger is never released
- Connector not fully seated, or a terminal pushed back out of its lock
- Corrosion in the switch connector creating an effectively open joint
- Internal open in one contact set while the other contacts still function
- Broken conductor inside the insulation where the harness flexes at the pedal bracket
- Aftermarket accessory installation that interrupted the brake circuit and was never restored
Symptoms
- Shifter refusing to come out of park with the brake pressed
- Brake lights not illuminating at all
- Push-button start declining to crank the engine
- Cruise control unavailable or refusing to engage
- Cruise control not cancelling when the brake pedal is pressed
- Check engine light with completely normal engine operation
- Fault appearing immediately after work under the dash or on the pedal assembly
- Brake lamp fuse found open when the fuse box is checked
Diagnostic steps
- 1.Pull the brake lamp fuse and look at it. This takes under a minute and it is the highest-value first move on this page. On a great many vehicles the brake switch is fed from a dedicated always-live fuse, and when that fuse opens the module sees exactly what it would see from a broken switch. People replace switches over this. Check the fuse.
- 2.Have someone press the pedal while you watch the brake lamps. All dark is consistent with the fuse or with an open ahead of the switch. Lamps working normally while this code is stored points instead at the second contact set — the one that reports to the powertrain module rather than the one that lights the lamps.
- 3.Test whether the shifter will leave park with the engine running and the pedal firmly pressed. A vehicle that refuses is confirming, from the driver's seat and with no tools, that the interlock is not receiving a brake signal either.
- 4.Back-probe the switch connector with the key on and press the pedal. If the circuit changes state at the switch but the module still reports it high, the fault is between the two and the harness is where you go next.
- 5.Halve the circuit at the connector rather than working end to end. Jumper the appropriate cavities to simulate a pressed pedal, briefly and with the wiring diagram open so you know which two, and watch live data. A reading that responds proves the harness and module are fine and condemns the switch.
- 6.Check the switch's mechanical position last but do check it. A switch that has backed out on its threads holds its plunger permanently released, so the contact never changes state — mechanically an open, electrically identical to a broken wire, and free to correct.
Repair cost
$1 – $420
The floor is a dollar, which is not a rhetorical device — a blown brake lamp fuse causes a real share of these and a replacement fuse is the entire repair. Above that, a brake switch is $15 to $70 and about half an hour, so $80 to $200 fitted at a shop. Repairing an open in the under-dash harness is the expensive branch at $150 to $400, because the labour is in locating the break rather than in fixing it once found. Diagnosis is $80 to $150. Because the shift interlock and the brake lamps often fail alongside this code, get it looked at rather than leaving it — a car that will not come out of park at the wrong moment is an inconvenience with poor timing, and dark brake lamps are a hazard to the traffic behind you.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with brake light switch replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.