Technical Check Engine Light on but no Error Codes Stored when read

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Technical Check Engine Light on but no Error Codes Stored when read

emskibaba

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Hi All!

First post so go easy on me :) There's a bit of a story to this one so please bear with me, but it relates to the check engine light coming on but the diagnostics check not finding any error codes.

(y)

Back in April, my check engine light came on and the code suggested an issue with the accelerator sensor. I was told it could be 6 days-6 months before it needed replacing, and sure enough, 4 months later, the light came on again.

I was on a long motorway drove so pulled over, turned the engine on and off a few times to clear the light, and carried on. The light came on again about 20 mins later, so I did the same again. On both ocassions I was driving in excess of 65mph.

I did the rest of the long drive home at under 60mph and didn't see anything then for a couple of weeks.

The light came on again after driving approx half an hour at approx 70mph. I cleared it, but it came on again (twice) so I resorted to getting RAC out and they found 2 codes - one was the throttle sensor, the other unknown. I got it to my usual garage, they replaced the pedal and cleared the faults.

A week later - again, after driving approx 20-30 minutes and at 65-70mph the light came on again. I cleared it, then the same happened on the return journey after driving about 45 minutes at 60mph. So, I got it back to the garage but they couldn't find a record of the light coming on/there were no codes stored. This is where I need your help guys!

Why would this happen? What could it be? Could it be the 'unknown' error code from a couple of weeks ago? Something completely different? The car 're-learning' (I've read about this but in all honesty, don't fully understand it).

Bizarrely, a colleague had the same thing happen with his Fiat 500X - the light had come on (unsure about length of drive or speed). It went off of it's own accord, then when taken to the garage, there was no record of a fault.

I am now feeling totally anxious when driving, daren't go any speed or distance, and subsequently spending a fortune on public transport, so any suggestions that you lovely lot could give me would be hugely appreciated!

It's a 59 plate Grande Punto (1.4) with approx 49,000 miles.
 
If you experience any problem, get it sorted within a week or so. Not weeks (or months).
Accelerator pedal and throttle sensor? One is done, second one not (ignored). Check it.
What else...bad earth connections, bad battery, bad alternator, faulty ECU.
Try different garage (previous guys are "part changers").
 
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100% agree with GP-PL, throttle and accelerator signals can be monitored with MES, why wouldn't you start from the beginning ?? What kind of diagnosis "scanner" was used by the garage ??

Cheers, bernie
 
Thanks all.

I was advised by several mechanics to only replace the pedal when the light came on again and I got it sorted quickly when it did.

I'm a complete amateur but desperate for advice so please forgive me asking - but what's MES? In terms of starting from the beginning, I thought I had :(

I don't know what kind of scanner they used, but I am considering going to a different garage if I have any further issues with it.

When the lights came on last time (and this is why I'm worried) there was no fault recorded/stored, even though the light had come on twice. The fact that this had happened with a colleagues Fiat made me wonder if this is a common Fiat issue - hence reaching out the the Fiat community! I've never come across it with other [non-Fiat] cars in the past.
 
Sorry, another question...

Is there any reason why the light would only come on when I've been driving for at least half an hour and/or at a certain speed?

ps I didn't mean to quote throttle sensor - it's just the accelerator sensor, which has been replaced.
 
MES is the dedicated FIAT software/diagnostic kit...most garages use SNAP ON etc,which tbh are good, but generic code readers.
If you want an accurate diagnosis then go to a Fiat garage or Fiat specialist.Most charge £40 but its money,and time well spent.

If your feeling your original 'diagnosis' was wrong/hasn't cured 'it' you could try going back and asking for a refund,or further free diagnosis ..being told 'no' aint gonna hurt none and at the least you'd know to avoid that garage in the future...imho that is..;)

So in conclusion...buy a version of MES or go pay a dedicated Fiat place.
 
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Sorry, another question...

Is there any reason why the light would only come on when I've been driving for at least half an hour and/or at a certain speed?

ps I didn't mean to quote throttle sensor - it's just the accelerator sensor, which has been replaced.

There is a possibility that one of the potentiometer built in the accelerator sensor is going wrong, as the ECU expects to read the same values on both potis (safety request)it would report any discrepancy as an error; But MAYBE it needs to "see" a certain amount of those discrepancies to throw the error message (to avoid fake detections). That would explain the time you need to drive before the error occurs. Also the poti MAY be deffective in a specific position, let's say 80% throttle, if you stay BELLOW this threshold you won't trigger the error. That would explain the speed you need to drive at before the error occurs...

MES would tell you what are the values for each poti.

BRs, Bernie

If someone here helped You fix -or better, understand- your issue, hit the thanks icon @ bottom right corner, it's free and makes us feel helpy ;-)
 
Thanks Nikrox - i had 3 different readers all tell me the same thing (in relation to the accelerator sensor) so I'm pretty confident with that. But I had the same thought about a Fiat dealership next time round...

Bernie, thank you - this is now starting to make sense.

Another question, if you don't mind (you've all been very patient with me!). I might have put 2 and 2 together and got 7 here, but could length of time driving be an issue due to the engine getting warmer and dirt expanding and affecting a sensor somewhere?! This was a suggestion someone else made....
 
"A week later - again, after driving approx 20-30 minutes and at 65-70mph the light came on again. I cleared it, then the same happened on the return journey after driving about 45 minutes at 60mph. So, I got it back to the garage but they couldn't find a record of the light coming on/there were no codes stored."

If you cleared it, then this should explain why the garage couldn't find any record.
You effectively erased it.
Before erasing it, consider taking a note of any P0 numbers first.
 
Keat63 - I thought that if the light just went off the error was still stored? Or have I been misinformed by a number of mechanics?

i know you can properly delete the codes but I wouldn't even know how to do that!
 
I've see EML lights extinguish and then there be no code stored.

I assumed when you said 'I cleared it' you did so with a code reader ?
In which case, you erased it.

If you don't have one, then code readers can be had for peanuts, and is worth having one for when the light comes back on again.
You should then potentially be able to grab the codes while they are still fresh in memory along with any pending codes.
 
Hi Keat63 - I don't have a reader, I literally turned the engine on and off a few times (believe it or not, as instructed by an RAC mechanic!) so it wasn't fully erased.

I am tempted to get a reader - recommendations welcome - but not sure it'll help with these errors that are ghosting me!
 
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