C0048: Brake Booster Travel Sensor
What to do
The brakes work, but the pedal may be harder than usual — on cars with an electric brake booster, considerably harder, because the assistance can drop back to a mechanical fallback. Test the pedal gently before setting off, leave more room, and get it looked at promptly.
What this code means
The brake booster travel sensor circuit has a fault.
This sensor measures how far the booster's internal pushrod has moved, which is not the same as how far the pedal has moved.
The difference is the point. Comparing pedal travel against booster travel tells the module whether the booster is actually following the driver — a gap between the two is assistance failing in real time, detectable before the driver feels a hard pedal.
On an electrically boosted system it does more than monitor: it closes the loop. There is no vacuum diaphragm following the pedal mechanically; a motor is asked to produce assistance and this sensor reports what it produced. Losing it can force the system into a fallback where the driver's foot does all the work.
The most important thing first: the car still stops.
ABS, traction control and stability control are all additions to a braking system that works without them. When the module finds a fault it switches itself off and hands back a conventional, fully hydraulic brake system — the pedal, the master cylinder, the lines and the calipers are untouched. You have not lost your brakes.
What you have lost is the help. Without ABS the wheels can lock under hard braking, which lengthens the stopping distance on a slippery surface and — the part people forget — takes away your ability to steer while braking hard, because a locked wheel cannot generate cornering force. Without stability control the car will not catch a slide for you.
So drive it, but drive it as though it were forty years old: brake earlier, leave more room, and be especially careful in rain, snow and on gravel.
Likely causes
Start here
- Faulty brake booster travel sensor · specialist
- Corroded or loose connector · specialist
- Damaged wiring harness · specialist
Less common
- Leaking brake booster diaphragm · specialist
- Faulty stability control module · 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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