SERV + ABS + ESP

I am experiencing what appears to be a common fault, where the SERV + ABS + ESP light comes on during a drive. It reliably comes on every time the car is driven!

Here's what I've done so far;

• Bought a new brake pedal sensor from Autodoc and fitted that.
• Inspected the front ABS sensors, saw clear damage on the driver's side sensor so replaced both front sensors.

Still getting the same issue though, so did a little more research (mostly on this forum) and realised that I needed to check whether the brake lights come on when the pedal is pressed. So, this evening I got my 8 year old stood behind the car while I operated the pedal and discovered that the brake lights do not activate until I'm applying full pressure to the pedal. You've only got to test that a couple of times before the lights ping on again.

Based on what I've read, the discrepancy between pedal actuation and brake light activation points towards brake pedal sensor being the culprit here - despite having changed the part.

Is that a fair assumption, and is it worth changing the brake pedal sensor again before doing anything else?

Have you actually plugged it in to see what fault is causing the issue?

Mine was a rear ABS sensor, but I only found that out after plugging in a code reader.

Daz... said:

Have you actually plugged it in to see what fault is causing the issue?

Mine was a rear ABS sensor, but I only found that out after plugging in a code reader.

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Yes, I did but got no faults showing. That said, the lights on the dash weren't on at that moment, but being a little new to this I assumed that codes would be stored.

The brake switch is adjustable, it's a ratcheting type plunger.

Keep adjusting it until you get the lights coming on with minimal pedal pressure.

Failing that it could be the steering angle sensor.

alexfwalker said:

Is that a fair assumption, and is it worth changing the brake pedal sensor again before doing anything else?

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Probably worth saying that there is virtually no adjustment in the sensor, but it doesn't appear to need any - it's touching the pedal and moves easily with it as the pedal is depressed.

JamesBryan said:

The brake switch is adjustable, it's a ratcheting type plunger.

Keep adjusting it until you get the lights coming on with minimal pedal pressure.

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This is partly what's mystifying me. When the pedal is not being pressed, that plunger is tight up against it. If you press the pedal, the plunger extends easily and is still touching the pedal when it's fully depressed. In other words, the sensor should be picking up if a fly landed on the pedal.

alexfwalker said:

This is partly what's mystifying me. When the pedal is not being pressed, that plunger is tight up against it. If you press the pedal, the plunger extends easily and is still touching the pedal when it's fully depressed. In other words, the sensor should be picking up if a fly landed on the pedal.

Click to expand...

Yeah I don't know why but they take more adjustment than just fitting straight from the packet.

JamesBryan said:

Yeah I don't know why but they take more adjustment than just fitting straight from the packet.

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That makes sense, but I've got nothing that I can adjust. I've played with the sensor and ratcheted the plunger out maybe a couple of clicks, but that's all there is. But as I said, it seems to be perfectly adjusted. It just doesn't seem to work the way I'd expect it to!

alexfwalker said:

That makes sense, but I've got nothing that I can adjust. I've played with the sensor and ratcheted the plunger out maybe a couple of clicks, but that's all there is. But as I said, it seems to be perfectly adjusted. It just doesn't seem to work the way I'd expect it to!

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You need to push it in a few clicks at a time to adjust, not pull it out.

JamesBryan said:

You need to push it in a few clicks at a time to adjust, not pull it out.

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Well blow me down with a feather... That plunger works exactly the opposite way to the way that I thought it did. So, I pushed it in all the way, fitted it, tweaked it a bit and got the brake lights just right. I've taken it for a brisk trot around the lanes and would've expected the lights to come on almost instantly. 15 minutes of varied braking and no sign of the lights at all. And the ABS is definitely working.

Gold star sir, thank you!

alexfwalker said:

Well blow me down with a feather... That plunger works exactly the opposite way to the way that I thought it did. So, I pushed it in all the way, fitted it, tweaked it a bit and got the brake lights just right. I've taken it for a brisk trot around the lanes and would've expected the lights to come on almost instantly. 15 minutes of varied braking and no sign of the lights at all. And the ABS is definitely working.

Gold star sir, thank you!

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Yeah it's opposite to what you'd think.

I had a similar issue past couple of weeks. SERV+ABS+ESP on. I replaced the pedal sensor and adjusted it so lights came on with tiniest press of pedal. Still no luck with lights.

Also had noisy FOS wheel bearing. Got that fixed but ABS sensor had been damaged. That got replaced as well.

Drove down the road, no cruise control. Then SERV+ESP came on (without ABS). I stopped, I knew what was wrong - brake switch set too tight. I pulled it out one click and all is good.

PaulH1971 said:

I had a similar issue past couple of weeks. SERV+ABS+ESP on. I replaced the pedal sensor and adjusted it so lights came on with tiniest press of pedal. Still no luck with lights.

Also had noisy FOS wheel bearing. Got that fixed but ABS sensor had been damaged. That got replaced as well.

Drove down the road, no cruise control. Then SERV+ESP came on (without ABS). I stopped, I knew what was wrong - brake switch set too tight. I pulled it out one click and all is good.

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I'm glad you posted this, as it occurred to me that I hadn't tested the cruise control after fixing the main problem. Sure enough, it wasn't working, but I pulled the plunger out one click and the cruise control now works perfectly and I no longer have the dash lit up like a Christmas tree. Win!