What it means
Brake pressure sensor M signal voltage below expected range. 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.
At a glance
- Usually lights the ABS or stability-control warning light
- The engine or gearbox may go into limp mode
How it works
Brake pressure sensor M reports hydraulic pressure to the brake control module, which uses the signal when managing ABS and stability functions. This code sets when the sensor M signal falls below the module’s expected electrical range, often because the signal circuit is grounded or has a poor connection.
Common causes
Most likely first.
- Signal wire shorted to ground
- Connector pins corroded - high contact resistance
- Harness chafing through insulation
Symptoms
- ABS warning light on
- ESC/stability control deactivated
- Possible reduced brake assist
- Speedometer may behave erratically
How to diagnose it
- Record freeze-frame data and read live pressure sensor M data to see whether the signal is low or changes when the fault occurs.
- Inspect sensor M’s connector and harness for water, corrosion, pushed-back pins, or insulation rubbed through to ground.
- With the code active, gently move the sensor M harness while watching live data to check for a connection that cuts in and out.
- Use the vehicle wiring diagram to check sensor M’s signal circuit for a short to ground and verify its supply and ground against the manufacturer's specification.
- If the wiring and connections pass, compare sensor M’s reading with actual brake pressure and test the sensor or control-module circuit as specified by the manufacturer.
Common fixes
- Clean and secure corroded or loose sensor M connector terminals.
- Repair chafed wiring or a signal wire shorted to ground.
- Restore a damaged connector seal or replace a connector with defective pins.
- Replace sensor M if its signal remains low despite a sound circuit.
Can I keep driving?
Drive cautiously only if the brake pedal feels normal; ABS and stability control may be unavailable, and brake assist may be reduced. Avoid high speeds and hard braking, and stop if braking effort or response changes.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.