Citroen, Peugeot and Renault ABS Pump ESP Fault: Brake Pressure Sensor Failure and How We Stop It Returning

This is one specific fault within our ABS pump and module repair service, and this page follows it from the first warning light to the refitted unit.

What does the brake pressure sensor fault look like on the dashboard?

The stability system is the first to object. The ESP warning lamp comes on and stays on — on most cars it is the amber car with skid marks trailing behind it — or the light in the ESP button stays lit. Pressing the button changes nothing, because the system has already taken itself offline.

The ABS light may come on alongside it. Together the two lamps can look like a wider braking failure, but on these cars the combination very often traces back to a single sensor inside the ABS pump.

• ESP lamp or ESP button lit, button unresponsive. The signature of this fault, and the reason it is widely known as the ESP fault.
• ABS lamp lit as well. Common, but not always present.
• C1301 or C1302 stored in the ABS unit. The code is what separates this fault from others that light the same lamps.
• A lone ABS lamp with a wheel-speed sensor code. A different fault. A sensor at the wheel or its wiring is the likelier cause, and our wheel speed sensor guide covers it.

While ESP is off the car has no stability control, and with the ABS light lit the anti-lock assistance has gone too. Normal braking usually remains, so the car still stops, but the systems that step in on a wet road or in an emergency stop are not there. Have it checked promptly rather than living with the lights. Our guide to how an ABS pump works explains what the unit does when it is healthy.

Which fault codes point to the sensor inside the ABS pump?

A diagnostic machine plugged into an affected car will usually report one of three codes from the ABS unit. All three name the brake pressure sensor directly.

All three codes read like a wiring or switch problem, and a sensible garage will look at the brake light switch and the connections first. That is reasonable and quick to rule out. When those are sound, the fault is inside the unit, and no amount of work on the car’s wiring will clear it.

The same internal-sensor failure logs under different codes on other makes: C1028 on Suzuki, and C0131 on Vauxhall and Opel. Those are covered on our Suzuki brake pressure sensor page and our Vauxhall and Opel brake pressure sensor page.

What does fault code C0040 mean on a Peugeot or Citroen?

What C0040 means: On Peugeot and Citroen cars, C0040 is logged by the ABS unit as a brake pedal switch fault: coherence with the pressure sensor. The switch and the pressure reading no longer agree. When the switch and its wiring test good, the cause is usually the pressure sensor built into the ABS pump, the same failure behind C1301.

The code describes a disagreement, not a culprit. Each time the pedal goes down, the unit expects the brake switch to register the press and the pressure sensor to see the pressure rise with it. C0040 says the two have stopped telling the same story. It does not say which one is wrong.

That is why the switch end is checked first, and rightly so. Your garage will look at the brake pedal switch, the wiring and connector that serve it, and the fuse that supplies it. A failed switch or a lost supply can log C0040 on its own, and putting that right at the car clears it.

When the switch, its wiring and its supply are all sound and C0040 keeps coming back, the other half of the comparison is the one at fault. On these cars that is the pressure sensor inside the ABS pump, living with the same engine-bay heat, vibration and pressure pulses that lie behind C1301. It also explains a familiar pattern: a new brake switch goes in and the code returns, because no switch can correct a pressure reading that has drifted inside the pump.

From that point C0040 is handled exactly like C1301 and C1302. Your garage removes the pump and posts it to us in Epsom, the sensor fault is confirmed on our own test equipment before any work is done, and the unit is remanufactured with our external pressure sensor in place of the internal one.

Why does the sensor inside a Mk60 unit fail when the old external ones rarely did?

Earlier ABS pumps did not have this weakness, because the brake pressure sensor lived outside them — mounted on the pump body, or near the brake master cylinder or servo. In that position it was far more reliable, and if one did fail it could be bought from a dealer or parts factor as a part in its own right.

The ATE Mk60 and the units that followed it moved the sensor inside the pump. It now shares a housing bolted to the hydraulic block in the engine bay, where it lives with engine heat, constant vibration and a pressure pulse every time the brakes are applied. It is a known manufacturing weakness, and on these units it is less a question of whether the sensor fails than when.

Building it in has two consequences. There is no longer a sensor to buy, so the dealer answer is a complete new ABS pump. And that new pump carries the same internal sensor as the one it replaces, so the same countdown starts again.

It also explains why the car reacts so strongly. The system relies on the pressure reading to judge how hard you are braking; when that reading stops making sense, it cannot trust its own stability calculations and switches ESP off. The hydraulics may be in good order, yet the dashboard behaves as though the braking system has a serious fault.

Which Citroen, Peugeot and Renault models and part numbers are affected?

These are the models we are most often contacted about with this fault. The list is not exhaustive: the Mk60 unit was fitted widely across all three makes, and across most other manufacturers too.

The model name only gets you so far. There are hundreds of part numbers across the Mk60 units fitted to these cars, and the number on your unit’s label is what identifies it. These are the numbers sent to us most often for repair or exchange, grouped by style so you can match your label quickly.

If your number is not listed, that does not mean we cannot repair it. Add it to the repair form, or ask us to check it before the unit comes off. For the rest of our ABS work on each make, see our Citroen ABS repairs, Peugeot ABS repairs and Renault ABS repairs.

New, used or remanufactured: which option ends the fault?

Once the code points at the sensor, you will normally be advised to replace the ABS pump. That advice is right about where the fault is, and less helpful about what happens next.

The refit matters as much as the design. A replacement unit, new or used, arrives knowing nothing about your car and has to be programmed or coded to it, which takes equipment able to talk to the car at manufacturer level. Our remanufactured units self-calibrate to the vehicle they are fitted to — and that includes an exchange unit, if you would rather receive one of ours than send yours in.

We do not simply renew the sensor, because that would put the weakness straight back. The remanufacture takes the internal sensor out of the job altogether, which is why we can warranty the unit for life.

How does our pressure sensor repair work by post?

The ABS pump is the only thing that travels. Your garage removes it and posts it to our workshop, and the car stays where it is.

1. Code and part number on the form

   The repair form asks for the model, what the dashboard is showing, any C0040, C1301 or C1302 reading and the number on the unit’s label. If something does not add up, we say so before the unit is removed.

2. Your garage lifts the unit out

   The ABS pump comes off the car and is posted to us, packed so the ports and connector are protected.

3. The fault is proved, not assumed

   The unit is tested before any work starts, so the sensor fault is confirmed on our equipment rather than taken from the code alone.

4. Remanufactured, calibrated, tested again

   Our external brake pressure sensor is fitted and calibrated to the unit, which then goes onto our Hardware-in-the-Loop rig to be run under simulated heat, vibration and load.

5. Back to the garage, ready to calibrate itself

   It refits without programming. The brake lines were opened to remove it, so the garage bleeds the brakes and clears the stored codes as part of the refit.

The work is carried out in a cleanroom-standard, ESD-safe workshop by our own team of electronic and hydraulic engineers.

Questions owners ask about the ESP pressure sensor fault