P05AF

Brake Pedal Position Sensor A Circuit Low

P05AF is a generic OBD-II powertrain diagnostic trouble code: Brake Pedal Position Sensor A Circuit Low. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.

Code
P05AF
Group
Powertrain
System
Powertrain
Severity
Warning (MIL on)
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What P05AF means

P05AF is set when the ECM or brake control module detects that the voltage signal from brake pedal position sensor A is below the minimum expected threshold. Brake pedal position sensors are typically analog voltage-output devices; a low circuit reading suggests a short to ground on the signal wire, loss of the sensor reference voltage supply, or an internally failed sensor.

Because brake pedal position data is used by multiple safety-related systems including traction control, stability control, and autonomous emergency braking, a low circuit fault may cause the module to disable or limit those features as a precautionary measure. The brake hydraulics are generally unaffected, so braking ability is preserved.

Diagnosis should confirm whether the low voltage condition is in the wiring or within the sensor itself. Disconnecting the sensor connector and observing whether the signal voltage rises to near reference level helps isolate the fault to the sensor versus the wiring. Reference voltage and ground integrity at the sensor connector should also be verified before any parts are replaced.

Common causes

Most-frequently reported root causes when P05AF is logged.

  • 1
    Brake pedal position sensor A internally shorted to ground.
  • 2
    Signal wire shorted to ground between the sensor and the control module.
  • 3
    Loss of 5V reference voltage supply to sensor A.
  • 4
    Corroded sensor A connector causing a leakage path to ground.
  • 5
    Damaged wiring harness near the brake pedal assembly.
  • 6
    Moisture intrusion into the sensor body causing internal short.
  • 7
    Control module reference circuit fault.

Symptoms drivers notice

MIL and possibly a brake system warning light illuminated.
Stability control, traction control, or ABS warning lights may also illuminate.
Advanced driver assistance features such as automatic emergency braking may be disabled.
Normal brake pedal feel and stopping ability are generally retained.
Possible hesitation in engine torque delivery if brake pedal signal is used for torque management.

How to diagnose P05AF

A typical diagnostic flow when this code is present.

  1. 1
    Retrieve all DTCs from all modules and record freeze frame data.
  2. 2
    With the key on engine off, measure signal voltage at brake pedal position sensor A connector.
  3. 3
    Check 5V reference voltage and ground at the sensor A connector.
  4. 4
    Disconnect sensor A and observe whether the signal voltage rises toward 5V.
  5. 5
    If voltage rises after disconnecting, the sensor is shorted internally and should be replaced.
  6. 6
    If voltage remains low after disconnecting, inspect the signal wire for a short to ground.
  7. 7
    Inspect the wiring harness routing near the brake pedal pivot for chafing or pinching.

Related powertrain codes

Frequently asked questions

Does P05AF mean my brakes are failing?

No. P05AF is an electrical fault in the brake pedal position sensor circuit, not a hydraulic brake failure. Your brake pedal and stopping ability are not directly affected.

How does a short to ground cause a low voltage reading?

When the signal wire is connected to ground unintentionally, it pulls the sensor output voltage down toward zero regardless of pedal position, causing the module to read a below-minimum value.

Can P05AF and P05AE appear together?

Yes. If sensor A is producing a low or zero reading, it will also fail to correlate with sensor B, which is operating normally. Both codes may be stored simultaneously.

Is brake pedal position sensor A replaceable separately?

On most vehicles the sensor is a separate component mounted on the brake pedal bracket and can be replaced independently. Some integrated pedal assemblies may require pedal box replacement.

Disabling P05AF in software

RaceTune can permanently disable P05AF — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.

Permanent
The monitor is disabled in the ECU itself — not just cleared. It cannot return.
Tailored to your file
Each patch is matched to your specific software version — never a one-size-fits-all file.
Reversible
The original file is always preserved. Reflash the stock to return the ECU to factory state.

Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.

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