OBD-II trouble code
P0724: Torque Converter/Brake Switch "B" Circuit High
The module is reading the brake switch input at the high end of its range. Before you decide what that means, find out from the wiring diagram whether high is the pressed state or the released state on your vehicle — it is not the same on every design.
Quick facts
- System
- Powertrain
- Category
- Transmission / Torque Converter
- Severity
- Medium severity
- Drivable
- Usually safe to drive short-term
- Repair cost range
- $0 – $450
- DIY difficulty
- Beginner DIY
What does P0724 mean?
P0724 is a voltage report, and that is the whole key to it. The controller is not saying the brake switch is faulty and it is not saying the transmission is faulty. It is saying that the voltage it measures on the brake switch "B" input has gone above the window it expects and stayed there. Everything useful about diagnosing this code follows from working out what a high reading physically corresponds to on the vehicle in front of you.
That sounds like pedantry until you look at how these circuits are actually built, because there are two arrangements in common use and they mean opposite things. In one, the switch supplies battery voltage to the module input when the pedal is pressed, so a permanently high reading means the switch is closed all the time — stuck, waterlogged, or held in by something. In the other, the module supplies its own reference voltage through a pull-up resistor and the switch pulls that line down to ground when the pedal is pressed, so a permanently high reading means the line is never being pulled down at all — an open circuit, a disconnected connector, a broken wire, or a switch whose contacts have burned open. Same code, same input, opposite conclusions and opposite repairs. A wiring diagram for the specific vehicle costs a few minutes and saves buying the wrong answer.
The second arrangement is the more common one on the vehicles that set this code, which is why the classic P0724 presentation is loss rather than excess: brake lamps that never illuminate at all, a shift lever that will not leave Park, and cruise control that refuses to set. Notice that this is a different complaint pattern from a switch that is simply out of adjustment. A misadjusted switch still works — it just works at the wrong point in pedal travel, so the signal is present but arrives late or early. An open circuit produces no signal ever, at any pedal position. If the driver reports that the brake lights have never worked since the fault began, adjustment is not the answer and no amount of resetting the plunger will help.
That difference should also change the order in which you test. Where a plausibility fault rewards watching live data through a full pedal stroke, an out-of-range-high fault rewards static electrical work: check the fuse, check for voltage arriving at the switch, check continuity from the switch through to the module pin, and check the ground the circuit relies on. A high reading caused by an open ground is common and is missed constantly, because a poor ground raises the whole reference and the switch itself tests perfectly on the bench afterwards.
One caution about the connector, because it is where these faults actually live. The brake switch connector sits at foot level under the dash — the lowest point of the passenger compartment wiring, directly beneath the pedal, where wet shoes, spilt drinks and a leaking heater core all end up. Corroded terminals there raise circuit resistance, and raised resistance on a pulled-up input reads as high. Green residue on a pin is a finding, not cosmetic damage, and cleaning or replacing the terminal is a real repair rather than a stopgap.
Common causes
- Open circuit between the brake switch and the control module, most often a broken conductor where the loom flexes near the steering column
- Disconnected or partially unseated brake switch connector, common after any dash, pedal or footwell work
- Corroded connector terminals at the switch, raising circuit resistance on a pulled-up input
- Switch contacts burned open on the module input contact set while the stop lamp contacts still function
- Blown fuse feeding the brake switch circuit
- Poor or missing ground for the switch circuit, which raises the measured voltage without the switch being faulty
- Switch stuck closed on circuits where a closed switch supplies voltage rather than pulling the line down
- Switch pushed permanently out of contact by a broken mounting bracket, so the contacts never make
- Aftermarket trailer wiring, alarm or remote start splice that has failed open or corroded at the joint
- Failed control module input, which is uncommon and should be the last thing considered rather than the first
Symptoms
- Brake lights that do not illuminate at all, at any point in pedal travel
- Shift lever locked in Park, requiring the manual interlock override to move
- Cruise control will not set or resume
- Torque converter clutch staying applied as the vehicle slows, causing a shudder or stall at a stop
- Check engine light with no drivability complaint otherwise
- ABS or stability control warning appearing alongside the engine light, since those systems use the same brake input
- Fault appearing immediately after dash, pedal bracket or footwell repair work
- Automatic emergency braking or adaptive cruise features disabled with a message in the cluster
- On circuits where high means stuck closed, brake lamps that stay lit permanently and a flat battery overnight
Diagnostic steps
- 1.Look up the brake switch circuit in the wiring diagram for the specific vehicle and determine whether the module input is pulled up or switch-fed. Until you know that, you do not know whether high means open or means stuck closed.
- 2.Press and release the pedal while someone watches the rear of the vehicle. Lamps that never light point at an open circuit; lamps that never go out point at a switch stuck closed.
- 3.Check the fuse feeding the brake switch circuit, and test it under load rather than by eye. A fuse can look intact and still be open.
- 4.Back-probe the switch connector with the ignition on and confirm voltage arrives on the feed side and that the ground side is genuinely at ground potential.
- 5.Measure voltage drop on the ground path rather than only checking for continuity. A high-resistance ground raises the reading on a pulled-up input and mimics a failed switch exactly.
- 6.Inspect the connector terminals for green or white corrosion residue. This connector sits at the lowest point of the footwell and sees more moisture than almost any other in the cabin.
- 7.Test continuity from the switch connector through to the module pin with the connectors separated, wiggling the loom near the steering column while watching the meter.
- 8.Check for aftermarket splices into the brake circuit from trailer wiring, alarms or remote start systems, and inspect any joint you find.
- 9.Verify the switch itself with a meter across its terminals, operating the plunger by hand. Test the module input contact set specifically, not the stop lamp contact set.
- 10.After repair, confirm all four functions the signal serves: brake lamps, release from Park, cruise control engagement, and converter unlock on deceleration.
Repair cost
$0 – $450
A blown fuse or a connector that has worked loose is effectively free to fix if you find it yourself, and about $90 to $150 if a shop diagnoses it. A brake light switch is a $15 to $60 part and roughly 0.3 to 0.5 hours of labour, so $60 to $190 fitted. Repairing corroded terminals or a broken conductor in the loom is where the money goes on this code: $120 to $350 depending on how much of the harness has to be opened up and how awkward the access under the dash is. A brake pedal position sensor, on vehicles that use one instead of a switch, runs $150 to $450 fitted. Because a high reading so often turns out to be a connection rather than a component, paying for diagnosis before paying for parts is unusually good value here.
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 a beginner-friendly repair. Common hand tools, a free afternoon, and a willingness to follow a procedure are usually enough. The risk of causing a bigger problem is low if you read up on your specific vehicle first.