How often do garages mis-diagnose faults?

[/\ndy]

So your car wouldnt start, you took it to him, he started your car.
Doesnt sound like a misdiagnosis to me?

Car would likely start with a knackered gasket (as you say, it was running like that for a while before the puddle incident), so once he has figured out that there was no spark and cleaned out the rotor cap to fix this, the car starts and there's no reason for him to go any further.

How wouldn't this be a misdiagnosis? Ultimately they never found the real problem.

 

[touch]

How wouldn't this be a misdiagnosis? Ultimately they never found the real problem.

edit: explained far better below

 

[p1RATE]

How wouldn't this be a misdiagnosis? Ultimately they never found the real problem.

When a car doesn't start there are three things to check fuel, compression or spark. In this case you have told the mechanic that you went into a deep puddle so the first thing to check is water interfering with the electric components in some way. Which is exactly what he has done, gone for the dizzy cap and cleaned it up to ensure the spark is being sent correctly. This appeared to have been the fault as the car functioned afterwards. It was not a misdiagnosis as the mechanic had no information that would require any further investigation.

Mechanic B knew that this did not resolve the problem so delved further as he had better information to go on.

 

[-Mike-]

So you guessed yourself and got lucky?

No, I was on the line of thought that my rev counter behaved the same in my 306 and that was the issue. My guess cost him absolutely nothing. The garage guessing cost him £50 diagnosis and a £1000 bill for a fuel pump if he went ahead.

He didn't guess, he looked on the database ( internet ) and saw what other dealers ( people ) had and found the cause.

The internet is a wonderful source of information, especially when its a common fault.

It could have been the wiring rather than the sensor, I doubt any actual testing took place.

Who, testing what? Actually we did test the resistance of it, it was fine when cold, when hot its readings were out of range.

 

[MatteH Oxford]

O.K. congrats, you actually did a test which is more than most would have done.

What would you have done if the sensor was in range i.e. appeared good?

 

[-Mike-]

If the sensor had been good - I would have traced the wire back to the ECU and checked continuity of that. After that - checked the ECU plug to ensure no corrosion.

After that - who knows we didn't get that far!

 

[Tute]

Not car related but I recently took pity on a friend of my Mum's. She was having internet trouble with poor connection speeds and dropouts and she paid "Purple Shirts" nearly £200 to fix it.

I say fix it, but apparently they came around, spent hours looking at it all, said they didn't know what was wrong, billed her for it and left.

I went in there, noticed immediately it was an old house with phone extensions a-plenty. Started unplugging them one by one and testing the speed. It took me 20 minutes to find the faulty connection.

I wouldn't accept any payment for it as I felt she had paid enough.

It's about time legislation is passed to stop companies charging for not actually fixing problems. I expect it would shake them into action and make them start training their staff properly, rather than relying on "computer says no" all the time.

 

[lordrobs]

I've had;

A faulty secondary air pump diagnosed as a faulty alternator.
A rattling piece of vent trim diagnosed as a faulty instrument cluster.
A wiring fault diagnosed as a faulty climate unit.

The second two I can understand as the wiring was related to the climate and tracing a rattle is often tricky but the first really wound me up as I specifically asked them to check the secondary air pump and they said it was fine.

 

[Fuzz]

So lets see..

The garages "font of all knowledge" was a box that spat out some possible causes..
The OP's "font of all knowledge" was the internet forums which spat out some possible causes.

Neither of you ACTUALLY investigated the symptoms any further than what the box said.
THIS IS THE PROBLEM!
You got lucky that is all.

 

[[TW]Fox]

So lets see..

The garages "font of all knowledge" was a box that spat out some possible causes..
The OP's "font of all knowledge" was the internet forums which spat out some possible causes.

Neither of you ACTUALLY investigated the symptoms any further than what the box said.
THIS IS THE PROBLEM!
You got lucky that is all.

The garage are 'experts'. They charge for 'expert advice' which they gave after using whatever tools they wanted to use to help them diagnose the problem.

 

[Fuzz]

clearly some level of "experts" are better than others

 

[[TW]Fox]

clearly some level of "experts" are better than others

They are, but if you encounter a rubbish one, you just end up paying loads more money for the extra time they take...

 

[-Mike-]

So lets see..

The garages "font of all knowledge" was a box that spat out some possible causes..
The OP's "font of all knowledge" was the internet forums which spat out some possible causes.

Neither of you ACTUALLY investigated the symptoms any further than what the box said.
THIS IS THE PROBLEM!
You got lucky that is all.

Sorry but what? I am NOT a mechanic.

The garage read the code and said 'fuel pumps dead, need new one £££££" charged for time reading code and taking the car for a test drive.

I read the code, listened to what he said and tallied the rev counter dropping to 0 (with my own previous experience), with the speed error relating to the fuel pump. Figured that the two may well be linked, looked online and found many others.

So I tested the values of the sensor, which as stated above were fine when cold, but when warm out of range. This points to a faulty sensor, does it not? So despite it not being my job I (as you put it...) DID investigate the symptoms and drew a conclusion that the part was faulty.

I'd also like to add, me looking, testing resistance and fitting the part cost my boss a whopping £38 for the part.

I fail to see your point to be honest Fuzz. I also don't think we 'got lucky'. The error code was relating to a speed reading, and the rev counter didn't work which would suggest the ECU was having issues with knowing what speed the engine was running at. The two kind of tie nicely together, no?

 

[Fuzz]

You said none of that in your OP.

 

[MatteH Oxford]

The first two things that I would have done (seeing as the fault occurs with the engine running), is to test the condition of the battery & connections & to do an alternator ripple test. This is what's known as an initial check, and it should be carried out before any electrical work commences on ECU circuits to rule both potential problems out. Modern computer controlled systems are highly sensitive to relatively minor faults in the battery and charging system, either a too high/low supply voltage or too much AC current in the DC supply.

O.K. you did "get lucky" so to speak and found the fault without having carried either test , potential faults found during these tests could have caused the issue(s) described. My sisters very own Zafira with a rev counter problem being a case in point (a bad alternator diode).

BTW, resistance testing components is pretty old school and rather hit and miss, I remember condemning a slightly out of range cam sensor on a Vauxhall as faulty when in fact it shared the same 5v reference circuit as the crank sensor. This was not apparent from the diagram I had, there was an intermittent short to ground problem with the crank sensor causing the issue (signal drop out, car stalling). If I had known the circuits were linked I would have checked both, shared ECM sensor circuits are notorious on some Vauxhalls/GM and a lot of people aren't aware of this. I wasn't at the time.

Another thing is that I used to hate testing/condeming MAF sensors on a vehicle where I didn't have a new one to easily swap out, because you can have one show out of range but still function perfectly o.k., it's difficult to test one fully using a ordinary multimeter.

Dynamic (live circuit) testing where the fault can be seen clearly in real time (or logged/recorded) is by far the best method of condemning the wiring or sensor (not for obvious short circuits though, check them first with the battery disconnected! ). Wiring can be checked via voltage loss & drop methods which are easily performed with a normal multimeter.

Lab scopes are a fantastic piece of kit for condemning sensors (especially MAFs) although not many technicians seem to either know how to use one or to have access to one.

 

[Jester*]

While being relatively ok with basic mechanics I am pretty OCD when it comes to finding a specialist garage relative to the make of car I currently own.

The Renault specialist I used to use, was absolutely fantastic and if I had any issues, apart from doing some research myself, they would always find the issue as it had appeared many times before without costing me an absolute fortune in a miss diagnoses.

So go hunting for a specialist you trust and it could save you a fortune

 

[lordrobs]

While being relatively ok with basic mechanics I am pretty OCD when it comes to finding a specialist garage relative to the make of car I currently own.

The Renault specialist I used to use, was absolutely fantastic and if I had any issues, apart from doing some research myself, they would always find the issue as it had appeared many times before without costing me an absolute fortune in a miss diagnoses.

So go hunting for a specialist you trust and it could save you a fortune

I've only tried two specialists but my conclusion was... I'd rather take it to the main dealers.

The first gave me a ring stinger of a quote for a full service and when I wanted to confirm exactly what that included they got very funny. I mentioned spark plugs (an obvious one I'd have thought) and he starts to go off on one. "Hang on a minute, this is the first time you've brought it to us, I don't know what its going to need. I need to see what has been done before." Ummm... yet you just gave me a very specific (and expensive) quote. I think I'll pass.

The second was the one that identified and fitted a new alternator for the faulty secondary air pump. They also gave me a selection of faulty or dangerous courtesy cars. For the slight saving over the main dealer they weren't worth it.

Both had a good reputation. I know this isn't always the case but it is a lottery, main dealers aren't perfect but when things do go wrong they tend to resolve them with the minimum of fuss and at no extra cost. At least that is my experience of Fiat and Skoda.

 

[Dogbreath]

So lets see..

The garages "font of all knowledge" was a box that spat out some possible causes..
The OP's "font of all knowledge" was the internet forums which spat out some possible causes.

Neither of you ACTUALLY investigated the symptoms any further than what the box said.
THIS IS THE PROBLEM!
You got lucky that is all.

Why are certain people criticising the OP? He did some research online, discovered the symptoms pointed to a common fault with an inexpensive sensor which he'd already experienced on his own car and this ultimately proved to be the cause of the problem. Obviously it could have been another problem, but the balance of probabilities means it was more likely to fix the fault than not, and it was a very cheap option. Replacing a perfectly good high pressure fuel pump would have cost the owner a ridiculous amount of money and not fixed the problem.

Garages misdiagnose problems all the time. Every single day hundreds of people will be given incorrect advice and will end up spending far more than they need to.

 

[OpenToSuggestions]

That's all they ever do now. Read codes, replace 'diagnosed' item, read more codes when it's not fixed.

This.

I visited an MX5 garage that did lots of work on MK1s.
Broadspeed I think it is called, in the middle of a roundabout opposite Asda in Stafford.

The bloke in there must be about 70 years old and said we don't have mechanics anymore, we have fitters. A mechanic takes a gearbox apart and repairs it. A fitter takes the old one off 'lol it is ****ed' and replaces the entire unit.
I do see his point.

 

[[TW]Fox]

Are there any other industries where incompetence is more profitable than competence?

Just randomly replace stuff and blag your way through, the more work you do, however much of its totally pointless, the more you can bill the customer for.