How often do garages mis-diagnose faults?

-Mike-

-Mike-

-Mike-

Soldato
Joined
22 Dec 2002
Posts
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Location
Minehead
Hey,

The assistant GM at work had a problem with his Zafira - symptoms included rev counter dropping to nothing, erratic idle and when the rev counter stopped working it would throw up two fault lights.

He took it to a local garage who read the fault codes and immediately said it needs a new fuel pump. He took it to Vauxhall, who said exactly the same thing. While the fault code mentioned the fuel pump surely alarm bells would ring with the rev counter dropping to 0 whilst the engine was running?

Typical lunch time conversation starts with everyone laughing as he's tight and didn't want to buy a new car. He tells us all the fault and everyone else laughs on. I had a thought, my 306 turbo screwmod tractor had an issue with the rev counter dropping off when it warmed up and it was a sensor. Quick - to the internet. Sure enough, many many threads about people with the same issues, being told the same by garages and even Vaux garages.

So, three days ago he picked up a CPS, we fitted it and guess what - the car is perfect. We suggested a double annual salary bonus for fixing his car but he didn't go for it ;)

Sorry if I've put you to sleep reading that but I wonder : How many garages carry out needless work due to a fault code and fail to think outside the box?
 
one garage fixed my dads car 3 times before he went to another garage and got it properly fixed lol..

dunno why he kept going back to his local one
 
Had the same with my Mazda - Common fault, mentioned by loads of posts on owners club forums, there was even a Mazda service bulletin which I printed out and took to the garage which basically said exactly what was wrong with it and what needed replacing. Unfortunately the only official sources I could find were from the US, so the SB had a different range of chassis numbers to UK cars.

Garage took one look at the SB, one look at my chassis no, and decided it couldn't possibly be the same fault, and they'd have to strip down the whole engine to diagnose it. Needless to say I declined, and took it back to where I'd bought it - they got their local guy to look at it. 20 mins labour + £15 part, exactly what it said on the SB...
 
I had national tyres misdiagnose mine only this past week, car wouldn't start after driving through big puddle any they said something like the dizzy rotor arm or something was damp and it wouldn't spark the ignition (no idea what he was talking about), so he said he cleared it out and applied some wd40, worked for a day then next morning same problem. Had a mobile mechanic come out, he found that the oil cap was all gungy, and basically water had got into the engine (would have been way before he puddle incident). He did a compression test and established the head gasket was totalled and needed replacing! I tell you, finding a reliable mechanic is an absolute nightmare!
 
/\ndy said:
I had national tyres misdiagnose mine only this past week
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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.
 
As cars become more complex and systems struggle to keep up, I'm not convinced it's getting any easier to diagnose some problems. If the issue is clear and shows up on a computer screen then all good, but those niggly issues that you know exist, but don't show up on a computer screen can be a real pain. It does become tiresome when a service manager trots out "we could see nothing wrong, so we have reset the big box and see how you go" only to drive 10 miles down the road and have the issue arise again.

I've even had complete brain farts of the on-board electrics that haven't even shown themselves come garage time. I had one a few months ago that I still can't fathom. Driving normally, car shuddered like a bucking bronco, everything lit up. Parked it, turned it off and back on and all was fine. Took it to the nearest BMW dealer and they found nothing, not even a syntax error!
 
touch said:
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.
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When i first read it the non start and HG failure sound like two separate issues.

Even if the HG causes the car not to start there must have been other symptoms before this like a loss of coolant. If that had been mentioned im sure there would have been cause for the mechanic to investigate further. As mentioned diagnosing a non start issue would not lead you directly to checking for HG failure.
 
Welcome to the motor trade. Why would they bother to become skilled in diagnoses, they just bill the customer for any wasted time or misdiagnosis.

If it takes them 5 hours to find a fault that's 5 hours of pay for them.
 
The big issue is that it's only going to get worse!

OBD can only tell you roughly what direction to look at, but without somebody that actually knows the system in and out, it often will be just trial and expensive error.
 
A lot of the time, the customer can send a mechanic on the wrong train of thought. Often a customer will try and tell the mechanic what the fix is.

Most of the time, the customer is just wrong.

See it all the time when repairing pc's/laptops etc
 
bledd. said:
A lot of the time, the customer can send a mechanic on the wrong train of thought. Often a customer will try and tell the mechanic what the fix is.

Most of the time, the customer is just wrong.

See it all the time when repairing pc's/laptops etc
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I'm nearly always correct when I put across my suspicions of what is wrong.

you have to word it carefully though with some people and make them think they have came to that conclusion by themselves ;)
 
I have to laugh how the sensors that are designed to alert the ECU to any problems are generally the item that has the problem!
 
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