P0571 means the engine control module detected a fault in the brake switch input used by the cruise control system. The family is P0571 (circuit), P0572 (low) and P0573 (high). Most vehicles have two brake switch signals: one that turns on the brake lights, and a second, often on the same switch body, that tells the engine and transmission modules the pedal is pressed so cruise cancels and the torque converter clutch releases. P0571 usually sets when the two signals disagree, or when the cruise input says "applied" with the pedal released.
Severity: low. Can you keep driving? Yes. Cruise control will not engage or drops out; the engine runs normally. On some vehicles the same input feeds the transmission's torque converter lockup, so a stuck "applied" signal can also mean the converter never locks and highway fuel economy drops. If the brake lights themselves are stuck on or off, that is a safety issue to fix regardless of the code.
Why the brake switch comes first
A British sports car maker's bulletin on this code says it directly: check the operation and adjustment of the brake light switch first, to rule it out before replacing an ABS module or chasing other cruise control causes. Porsche filed a bulletin in April 2016 on abnormal driving behavior with P0571. And General Motors preliminary information PIT5179A (November 2016) for the 2007 to 2014 Cadillac Escalade, Chevrolet Avalanche, Silverado, Suburban, Tahoe, GMC Sierra and Yukon explains the mechanism that fools technicians:
The scan tool parameters "BPP Circuit Signal" and "TCC/Cruise Brake Pedal" show Applied with the pedal released. Those parameters come from circuit 6311, which every module on it except the body control module feeds with a low-current reference of about 9 V; the body control module pulls it near 0 V when the pedal is released. A properly working circuit reads about 12 V with the pedal applied and near 0 V released. When the body module's pull-down is lost through an open or high resistance in circuit 6311, or a terminal problem, the modules see about 9 V and read it as "applied," and cruise refuses to work. The fix is the wire and its terminals, not the switch and not the modules.
Causes, in the order they are found
A brake light switch out of adjustment or with worn contacts, so one of its two signals changes state before or after the other, or not at all.
An open or high-resistance wire or terminal on the cruise brake input, as in GM's circuit 6311.
A corroded or backed-out terminal at the switch connector or at the module, especially after switch replacement.
A blown brake light fuse or a failed brake light circuit on vehicles that derive the cruise input from it.
A stuck pedal return or a pedal bracket that lets the pedal sit slightly down.
The module, last.
A diagnostic order
- Watch the brake switch parameters live. With the pedal released, both brake signals should read released; press slowly and watch them change. A signal that reads applied at rest, or that changes at a different pedal travel than its twin, is the fault.
- Check the brake lights with the pedal released and pressed.
- Inspect and adjust the switch per the manufacturer's procedure; many are self-adjusting by pulling the plunger out and letting the pedal set it.
- Measure the cruise input wire at the module with the pedal released: near 0 V on designs with a pull-down (GM's 6311), near 12 V pressed. About 9 V released on those GM trucks means an open in the pull-down path.
- Repair the wire or terminal, or replace the switch only if it measured wrong, then clear the code and verify cruise engages on a road test.
Frequently asked questions
Can I drive with a P0571 code?
Yes. Cruise control will not engage and the engine is otherwise normal. If the brake lights are stuck on or off, fix that first for safety.
Is P0571 the brake light switch?
Most often, or its adjustment. But on 2007 to 2014 GM full-size trucks and SUVs the usual cause is an open in circuit 6311 that leaves the cruise input at about 9 V, which the modules read as "brake applied." Measure the wire before replacing the switch a second time.
Why does the transmission also act up with P0571?
Because the same brake input tells the transmission to release the torque converter clutch. A signal stuck at "applied" keeps the converter unlocked, which shows as higher rpm at highway speed and worse fuel economy.
How much does it cost to fix P0571?
A brake light switch is an inexpensive part with a short replacement. A wire or terminal repair is under an hour. Modules are last on the list and rarely the cause.
Related codes
- P0572 / P0573: brake switch A circuit low or high.
- P0504: brake switch A/B correlation, the two switch signals disagreeing.
- P0565 to P0570: cruise control switch signals; see P0565.
- P0703: brake switch B circuit, the transmission's view of the same input.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.