You're better off taking your motor to a competent auto electrician, they really are good at these things when the weirdness starts

Our Citroen HDI totally conked out after an intermittent service fault bleep for about 2 weeks each time the car was started

in temper, the Mrs opened the bonnet and battered the plastic casing top covering the battery

…and the car worked perfectly after that

Now we whack it with a garden hand tool if it plays up

All the connections seem to be fine but something obviously isn't, large temperature changes seem to set it off and battering it sorts it out

With the Merc van the abs fault was actually crap software and a dealer upgrade sorted it out

There's a reasonable chance that a good auto electrical guy has already seen your fault before now

Edited By Ady1 on 14/09/2022 00:20:58

I wouldn't let a spanner monkey dig about with your electrics, even if he was the cause

Modern car electronics are a riddle wrapped in a mystery inside an enigma to me. I had, apparently, one LED fail in a rear light cluster on a Volvo V90 which brought up all sorts of intermittent and contradictory fault indications on the dashboard. The local Volvo specialist (after many years no longer an authorised Volvo dealer) had it in the workshop for a week before they found the fault and charged me £675. Obviously, I had no choice other than to smile through gritted teeth and cough up.

When my wifes car broke down the AA came out and towed it to a garage as the fitter said he could not look for electronic faults on the roadside. A full AA check on a car costs £128 for AA members (£142 for non-members),

regards

Very Much agree

Very much agree.

It is probably impossible to be sure one way or another.

Intermittent ABS light could be indication of some loose connection or other failure which just happens to get worse after MoT.

OR maybe they had a look, didn't find anything, but failed to connect the speedo wires back up solidly.

OR, in fixing the blower, they had to disconnect the speedo (not uncommon), and didn't plug it back in correctly.

I'd be slightly dissapointed with this : "'had a word' with the chap who had done the MOT and he said that the speedo/computer failure was because of the ABS fault".

Was MoT guy the same who originally noticed the fault (and implied it needed looking into)? If not, did they look into the fault? Check your bill… does it include any fee for investigation? Did they fiddle with speedo during the blower fix?

Ideally I'd want a garage that showed a little more concern.

The ABS system is also used by the speedo, Odo and the traction control if you have it.

Intermittent faults sooner or later become permanent. Reluctor rings break for no apparent reason, but these either fail or work OK there is no maybe.

It might the worth (after checking the fuse for the dead screen) checking the cables going to both front hubs for signs of scuffs in the dirt coating which may indicate interfering fingers or someone dropping the wheel on a cable when the tyre was changed.

BTW Don't go back there next year

Edited By Dave Halford on 14/09/2022 09:54:34

I had an intermittent ABS fault, eventually fixed by expensively renewing the relevant hub with rotor and sensor.

I think that the fault should result in an MOT failure.

That's probably a pretty fair application of vehicle inspection and repair experience.

Plus sometimes it's not just the nature of the fault itself but what it exposes of the skills and understanding of previous workers on the vehicle, and what other matters might have been affected.

I'd rather trust a vehicle to somebody who works like that than one working solely from a ticksheet.

Sounds to me like they "broke" the instrument cluster when changing the blower. You are correct a faulty speedo is an MOT failure.
Did they tell you about these faults when you picked it up?
The problem is proving it was them, however the speedo must have been working at the date and time recorded for the MOT. The probability of it failing overnight at worst is tiny. Any reasonable person would agree. If it did just happen to fail while the car was in their care that's just a cost of doing business. I would suggest you talk to them nicely and say that it most have been something they did and ask them to commit to fixing it, either themselves or by a specialist at their cost. If they don't agree to this tell them that you will get it fixed elswere and recover the costs from them by means of the small claims court. If they still refuse go ahead and get it repaired and open a claim. It's easy to do on line and low cost. Even if the garage does not pay up right away and it goes to a judgement if ther is any doubt in cliam aginst a business the judgement goes in favour of the consumer.

You don't say the make model or age of the car but this sort of fault can literally write off a modern car. It could need a whole new instrument cluster costing thousands. Some models of car you can't even fit a used one because they are "coded" to the car. With a used cluster you may end up with incorrect mileage which reduces the value of the car.
Technically you should get the speedo fixed ASAP as it's a safety issue. At least put a GPS with speed readout in the car so you can avoid a speeding ticket.

I had a similar issue with a trusted local garage. They changed the front spring on SWMBOs Focus and next day I noticed the headlamp levelling wasn't working. They had broken the link between the lower arm and leveling sensor. They tried to deny it initally but finally agreed to the logic. They had to replace the whole sensor. He showed me the bill for the part from Ford, it was more than we paid for the service, spring and MOT. 90% of Focus models don't have this sensory and the just let the arm and hub drop down like normal.

Robert G8RPI

Edited By Robert Atkinson 2 on 14/09/2022 17:44:50

Inoperative speedo could be as simple as not seating the connector properly when refitting the instrument cluster.

It would help to know what the car is, as the ABS fault could be relatively easy to diagnose – the Bosch ECUs used on 2000ish BMWs/Audis/Omegas/etc are known for faulty joints and can be repaired for far less than a new replacement. Losing the speedo is one of the associated faults. These systems require more than a basic OBD code reader to diagnose, but have been around long enough that any competent garage will should be able to do the work.

I've had several cars without working speedos pass the MOT.

The brake test is hardly brutal, and if a rusty pipe bursts during one then the test is serving its purpose. Far better than for it to fail in service. Additionally, I think any brake pipe that's been greased to extend its life should be an immediate fail.

The OP's garage doesn't sound very customer friendly…

.

But if Robin wants to submit the form that I linked earlier … that’s one thing he must not do.

MichaelG.