C004A: Brake Lining Wear Sensor
What to do
Have the brake pads inspected. This sensor is designed to be worn through by the disc, so the code often means exactly what it says — the pads need replacing. If you hear a grinding or harsh scraping noise when braking, stop driving and have it recovered: that is metal on metal, and it ruins the discs quickly. If the pads turn out to have plenty left, the fault is the wiring or a sensor left unplugged at the last service.
What this code means
The brake lining wear sensor circuit has a fault, or the linings are worn.
A brake wear sensor is designed to be destroyed, which is what makes this code ambiguous by nature.
The commonest type is a loop of wire moulded into the pad. When the friction material wears down far enough, the rotor grinds through the loop and the circuit goes open. So "open circuit" is the intended success condition, not a malfunction — the sensor reports wear by failing.
Which is why this code should be read as "check the pads" first and "check the wiring" second. A damaged cable, a connector left unplugged after a pad change, or a sensor not transferred to the new pads produce the same open circuit.
A sensor not reconnected during a service is a genuinely common cause, and it leaves a car whose next set of pads will wear out with no warning at all.
Do not ignore it on the assumption it is the wiring. Worn-through pads mean metal on metal: the braking is much worse, and the rotors are being destroyed at a cost several times that of pads fitted in time.
Likely causes
Start here
- Worn brake pads · moderate
- Sensor left disconnected after previous work · easy
- Damaged wiring harness · specialist
- Corroded or loose connector · specialist
Less common
- Faulty brake pad wear sensor · specialist
Symptoms
Components involved
Information, not instruction
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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.
Community experience
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