C0091

What it means

The brake pressure sensor signal is outside the plausibility band relative to pedal application. Wiring faults of this kind typically come from chafing, water ingress at connector seals, or pin push-back — a wiggle test on the harness while the code is active often confirms the location.

Is it safe to drive?

The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical.

Most likely causes

• Sensor drift with age

  high

  One of the most commonly reported causes for this code — check this first.

• Internal hydraulic block leak

  low

  Less common, but worth ruling out after the more likely causes.

• Sensor element aged beyond calibration window

  low

  Less common, but worth ruling out after the more likely causes.

Related help

• Full C0091 diagnosis, causes & costs
• How to read check engine light codes
• Is it safe to drive with the light on?