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Old 25-05-2018   #1
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Help with understanding some ECU readings - P1171

My partners Fiat 500C 1.4 16v 2009 (35k miles) has had this engine light fault for years and no one has managed to find the issue -P1171.



I have taken it to a number of Fiat specialists who say, its an intermittent fault and the engine is running fine (fuel trims and oxygen sensors etc are reading within the parameters). MAP, spark plugs, coil packs, pre cat oxygen sensor, fuel pressure checked etc have been replaced.


I would appreciate someone with the tech know how to take a look at the freeze frame ECU readings below at the time the fault was triggered and suggest where the fault may be. I suspect a wiring or short issue.



Thanking you in advance


Soc
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Old 25-05-2018   #2
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Re: Help with understanding some ECU readings - P1171

Whilst I can't help, does the light come on and off or once on stays on? Code seems to indicate a too lean mixture

Also what(anyone) happens at mot time, now with the new regulations with a "warning light" on, on the dash, is that now classed as a fail?

Here's a Google page vacuum leak is possible but given its been to several specialists arm chair diagnosis is not a reliable source of finding the fault?
https://autoservicecosts.com/obd2-codes/p1171/
http://p1171.engine-trouble-code.com/
http://abmforum.com/fiat-punto-code-p1171.html

This is a interesting read
https://www.justanswer.co.uk/car/a2r...-2009-1-4.html
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Last edited by John202020; 25-05-2018 at 16:25. Reason: more info
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Old 25-05-2018   #3
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Re: Help with understanding some ECU readings - P1171

As John says, we can only guess and if a "specialist" can't identify it we hae little chance.
However what diagnostic software did the garage(s) use? The screenshot you show does not appear to be from Fiat specfic diagnostics.

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Old 25-05-2018   #4
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Re: Help with understanding some ECU readings - P1171

P1171 is a Fiat specific code, not a generic code that all manufacturers use (they start P0***).


It relates to a mixture correction issue.
Basically, when power demand is high the PCM enters a power enhancement mode for fueling, but due to an issue somewhere, it runs out of references stored in the PCM to work out and supply the correct mixture, it just hasn't the figures stored in the tables it uses as references to mix up the right fuel and air for the demand.


It's usually due to something throwing a sensor out, like an small air/vacuum leak, exhaust leak up stream of the O2, slow O2 switch, but can also be due to fueling issues like clogged injectors, low fuel pressure, defective evap system or incomplete combustion due to ignition or compression problems.


It'll only flag when is detects the same problem two or three times in a single drive cycle and will usually reset it's self between drive cycles, but will more than likely store is as a pending all the time.



Dealers and garages don't really know how to track faults like these down as they take a bit of skill and the code doesn't really point to one thing, but you might have better luck with a proper diagnostic specialist.
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Old 26-05-2018   #5
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Re: Help with understanding some ECU readings - P1171

The giveaway to this is I believe the voltage below threshold. I had an error that repeatedly came back. Not the same one but I changed throttle pedal, throttle body, reset the code and as soon as I pulled away it bleeped and came back.

I took the car to a local trusted garage who had it for nearly two weeks and did numerous tests. It ended up being the body computer under the bonnet which apparently had two live signals one of which was an amp under the other so threw up the potentiometer fault. It was nothing to do with the potentiometer but the low amp signal fooled it into thinking there was.
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Old 27-05-2018   #6
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Re: Help with understanding some ECU readings - P1171

Thank you all for your suggestions.


Fuel pressure, injectors, coil packs, spark plugs, throttle body, oxygen sensors, MAP sensors, vacuum pipes & leaks all checked and fine. Fuel trims including short & long are normal and fuel economy is normal - 40 + MPG.


I personally do suspect an electrical anomaly which is causing the fault and as mentioned in the posts, the usual dealership and garage has limited skills in dealing with this type of fault.


typecastboy - the ECU/Body computer throwing out a false reading (low amp signal reading) sounds possible. How was this fault detected and how was it fixed? Is it something I can do or is it a specialist job?



Thanks again,
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Old 27-05-2018   #7
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Re: Help with understanding some ECU readings - P1171

Quote Originally Posted by soc View Post
Thank you all for your suggestions.

typecastboy - the ECU/Body computer throwing out a false reading (low amp signal reading) sounds possible. How was this fault detected and how was it fixed? Is it something I can do or is it a specialist job?



Thanks again,
not something that MES could do. It was that that gave me the bum steer to it being the potentiometer. It was a process of elimination to get to that conclusion. Basically it had a electrical signal that went back and forth from sensor to ecu and there were two of them with half an amp difference. I think they eventually got someone in. I bought an ECU on eBay for £60 and it was virginised for £100. Problem fixed. I think itís a specialist job with the right electronic equipment.
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Old 28-05-2018   #8
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Re: Help with understanding some ECU readings - P1171

Quote Originally Posted by soc View Post

Fuel pressure, injectors, coil packs, spark plugs, throttle body, oxygen sensors, MAP sensors, vacuum pipes & leaks all checked and fine. Fuel trims including short & long are normal and fuel economy is normal - 40 + MPG.

Fuel trims are worked out in closed loop and this codes doesn't relate to closed loop, so trims will look normal under normal running/idle conditions.



This code is a power enhancement related code, clog the throttle suddenly and it comes out of normal closed and into PE mode, so data from wide open throttle needs checking as it's complaining it hasn't the pre set data within the PCM to adjust the mix correctly under these conditions.
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Old 29-05-2018   #9
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Re: Help with understanding some ECU readings - P1171

Goudrons - Thanks for the information, what you are saying makes sense.



You refer to :


This code is a power enhancement related code, clog the throttle suddenly and it comes out of normal closed and into PE mode, so data from wide open throttle needs checking as it's complaining it hasn't the pre set data within the PCM to adjust the mix correctly under these conditions.'


Any idea how I can start to fix this issue myself, or do I need to give it to an expert?



I would appreciate any help or guidance to finally resolve this fault after so many years.


Cheers
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Old 29-05-2018   #10
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Re: Help with understanding some ECU readings - P1171

It would probably be easier to find a decent diagnostic service.
And I don't mean a grease covered man with a generic scan tool!
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Old 26-05-2019   #11
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Re: Help with understanding some ECU readings - P1171

Hi, The issue got resolved finally? Any findings? My 1.4 GP Fire exactly behaves the same way with P1171, 72. Root cause not found yet. In case if you narrow down the root cause, kindly share
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