QOTW #55 – HELP! DSC error light on my dashboard?

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Welcome to BamfordRose and another question of the week. This week it’s “help my DSC traction control, ABS light is flashing at me on the dashboard what do I do? What’s gone wrong?”

DSC (Dynamic Stability Control), is the feature that keeps the car on the arc that you’ve requested from the steering wheel. If it thinks you’re understeering, oversteering a bit, it’s going to grab some brake depending on which corner. So, the computer forces the car to take the angle of the arc that you’ve got set on the steering wheel. So, that’s Dynamic Stability Control, ABS is obviously Anti-lock Brake System and these two features work off the same circuit, obviously, the brake circuit. Traction control that’s something completely unrelated. This is when you’re giving it too much right foot, the engine ECU backs off the throttle to stop wheel spin. So, really common on early V8 DB9 for them to flash this DSC ABS error.

It’s going to be, well, normally, one of four things. First one will be the pressure sensor and the reservoir master cylinder area about 80 quid, take about 2-3 minutes to swap over and it’s pretty common for that sensor to fail. If it’s likely to be that, it’s probably going to do that key on immediately instead of needing to go above what it is, five mile-an-hour as the system performs a sanity check. So, if you’ve got a key on, it’s probably that sensor.

Next, the likely area will be a bit of wiring harness failure, so as it comes out the main loom to each corner is susceptible to corrosion. It’s very easy for those wires to crack a bit, get a bit resistance and it might pass the continuity check but the resistance in the circuit means that the body module, break module, detects that there’s a failure going on and it’s pretty common to renew that bit of harness. Really simple, easy bit of work to do, nothing to get worried about.

The next, it’s an actual failure with the sensor itself. I don’t really ever see this too much because what is more likely and means it isn’t the sensor. It’s the last thing which is the actual wheel bearing itself. On the back of the wheel bearing, there is the speed pickup signal that the sensor detects and it’s very common especially on the older cars for some corrosion to corrupt that signal and the brake control module computes that as a failure and pops the light on. If it is that one, I think you’re more likely to get that on the move rather than key on and the problem is there to start with.

So, wheel bearings are about 286 quid, a piece hour so to fit each of the sensors whether it’s wheel speed or the master cylinder pressure sensor about 80 quid each. And the wiring harness, well, that’s more than likely just a little bit of labour. To diagnose which fault you have, you’re going to need to plug the laptop on the car, obviously the factory laptop that we’ve got is going to tell us whether it’s electrical, mechanical failure. So, mechanical is going to be the wheel bearing, electrical it’s going to be harness or a reading from the pressure sensor, if it was that.

Maybe if you’ve got one of these clever OBD scanners which look at body modules, brake control modules, it might tell you the same, I don’t know. But any scan tool which won’t read the body module, brake control module, and just reads engine ECU isn’t really going to tell you what’s at fault unfortunately. So, it will need a bit of a laptop diagnostic to figure out what’s wrong. But most cases, the fix isn’t serious because it’s one of the four reasons I just stated.

The one where it is a bit of a problem is if it is the main brake control module itself that’s failed. I think they’re about 1200 pounds, so they’re very expensive. And again, you’ll only know if it’s that fault if you plug a laptop in and there’s some error signals from the brake control module itself. But, you know, it’s got to be 9 out of 10 cars here that come in with the DSC light on. It’s one of the four relatively easy ones to fix, so I wouldn’t get worried about needing a brake control module.

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