Started 29th October 2021
Starting a long drive home (Vauxhall (Opel) Insignia 1.4 T 2016, 20K miles) I came to going down a big hill, in 4th gear, taking my foot off the accelerator and expecting the car to roll smoothly along using engine braking. Instead it started to speed up and slow down, shortly afterwards the ABS (anti-lock braking system) and ESC (electronic stability control) lights came on along with a warning message "ESC Service".
I stopped, and then restarted, this got me more warnings, brake clutch fluid light, power steering service message ("Drive with care!"), parking assistant not working message (at 60 MPH?), along with both speedometers showing zero and when I stopped again, failure of the electric hand brake.
At this point I diagnosed car computer failure and called the AA. The person who came connected a computer to the car and said the problem was the drivers side wheel speed sensor, he cleared the error and I was able to drive home with the car behaving normally.
Cars know how fast the wheels are rotating and can then apply braking to individual wheels to allow for the wheels slipping. This is ESC or traction control. ABS observes wheels slipping when braking and reduces the braking.
The problem did not happen again until I repeated the long journey on the return leg of which it occurred the first time (and it went wrong in the same place). The next week I took the car to a local garage who could not reproduce the problem, eventually they replaced the drivers side ABS cable and returned the car saying it was not right "it speeds up on its own".
The speeding up thing sounds odd, I interpret it as ESC erroneously applying the brakes whilst the car is accelerating and then when the acceleration reduces, releasing them and causing the car to speed up.
I carried on repeating the long journey and having the car give the ABS/ESC warnings. Once those warnings appear the car goes into what is called "safety mode" or less properly "limp mode" with restricted acceleration. It is not a happy situation to be in and it would persist all the 50 miles home. The next day after a restart and reaching 30 MPH the warnings would clear.
I took the car to the main Vauxhall dealer, they said they could not make it go wrong, but the number of different stored error codes made it impossible to decide where the problem was. Like the first garage they had looked at the drivers side sensor/wheel and found nothing.
I carried on. More problems appeared - the "check engine" aka "malfunction" light. Being told to change into the gear I was already in. ABS activity - ticking (from the ABS pump), pressure on the brake pedal, and variations in braking effect. A warning about running out of fuel when going around a roundabout. There were more episodes of no speedometers/power steering warnings, thankfully fixed by stopping and starting. Sometimes the indicated speed changed instantly by 10 MPH - with no apparent acceleration. It would have been interesting to compare the speed shown with a GPS speed indicator.
Throughout I was trying to work out how to make the car go wrong or how to make it go right. There was a large random component, it would have good days and bad. On a bad day it would be showing subtle symptoms like the ABS pump ticking before I got half a mile from home, driving around town at 30 MPH such symptoms would go away. For the full ABS/ESC/limp effect a long trip including 70 MPH travel was needed. Keeping the speed below 60 it was possible to avoid it.
My guess is that a bit of real wheel slippage added to the error would be enough for the computer to mark the wheel sensor as bad. Or maybe it was just a case of speed making the problem worse.
It came to pass that the car was to go to the dealer again. On the day, it set off misbehaving and I took it via the Motorway allowing me to go at 70 MPH and get it into the ABS/ESC/limp mode. The result was:
"Carried out diagnostic checks for ABS, ESC and traction control warning light- Found code stored for erratic signal of right front wheel. Removed right front wheel, removed driveshaft, removed speed sensor and found marks on sensor. Further checks found ABS pick up ring has come out of wheel bearing. Supplied and replaced OSF wheel bearing assembly."
A text book fix - but only after 11 weeks.
And the moral is, don't assume the stored error code is going to solve things, the resolution needed the problem to be actually present. For much of the time I assumed there was some rare fault - which is a possibility - yet at the end it was a common problem.
In the above I have glossed over the difference between traction control and ESC (I know no better). There's a button on the dashboard to turn off one or both. Turning them off would have stopped some of the effects, like speeding up and slowing down, but turning them off did not prevent going into the ABS/ESC/limp mode.
Started 29th October 2021