Why does my car feel more responsive after a fault code reset?

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kpm

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Hi

I've read this phenomenon is fairly well-known, but what causes it and - perhaps more importantly - how do I keep it?

Even with no fault codes recorded, clicking on 'clear fault codes' still triggers a more responsive car - for about two days. Whether it's a fuelling reset or the car 'learning', how do I get it to learn that this is how I always want it to behave?

Thanks, Kristian
 
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kpm

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I don't know how to fix trims. No observations yet. I was considering earlier today what values/sensors I should look at for comparing the less responsive car and then immediately after a reset, but apart from the obvious like turbo and A/F ratio I would need to ask here what data I should be looking at.
 
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kpm

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My initial question was about a "phenomenon", it would not occur to me that I should include a complete auto-scan and read the self-help guides and "do my part and self-educate". There are no fault codes, and nothing is inherently wrong with the car. Indeed, my question was not technical so I did not think it would require a technical answer. Not every question requires a full auto-scan and the reading of all the self-help guides, as is evidenced by my other thread I posted tonight that required neither, and was helpful, and is fully resolved, for which I am very grateful.

As you have suggested in your last post that I need to read the technical help, do I understand that maybe there is a technical answer to be had and it is actually possible to fix this phenomenon?
 
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kpm: I definitely don't have the answer to your interesting question - if indeed there is an answer (it's not a phenomenon that I've ever experienced).

But, assuming that the "effect" is not psychosomatic (no offense intended, but it is possible, perhaps even probable after clearing DTCs and thinking all is fixed) - I wonder whether it happened in this particular case because of nature of your particular DTC.

If the car in question is the vehicle in your other thread, the DTC related to the Oxygen (Lambda) Sensor and more importantly the fault status was reported as "Intermittent - Not Confirmed".

This being so, a reasonable working hypothesis might be that the sensor simply flipped-back into operational mode after resetting the errors (coincidentally - not related to the error reset) and the vehicle response felt better - maybe, I'm guessing of course?

Don
 
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Jack@European_Parts

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We could query the Ouiji board instead and try to figure it out?�� :p

So still no auto-scan, new member wants to argue, WHY?


Did you know that even though a fault code is not present it doesn't mean that something is operationally parmount?

Ever look up FOD?
 
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kpm

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We could query the Ouiji board instead and try to figure it out?�� :p

So still no auto-scan, new member wants to argue, WHY?


Did you know that even though a fault code is not present it doesn't mean that something is operationally parmount?

Ever look up FOD?
It was 11pm, will post auto scan when it’s daylight. My friend I do not wish to argue, I know better than to bite the hand that feeds! Your use of words, you come across short, sharp and belittling - I don’t know if intentional and I have done something to upset you?

I did not know that no fault code meant that there could still be an issue, clearly I am under-utilising the VCDS here.

I do intend to read all of your links and post a full auto-scan today, for I am grateful for the assistance and the more I can teach myself the better for all.
 
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kpm

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kpm: I definitely don't have the answer to your interesting question - if indeed there is an answer (it's not a phenomenon that I've ever experienced).

But, assuming that the "effect" is not psychosomatic (no offense intended, but it is possible, perhaps even probable after clearing DTCs and thinking all is fixed) - I wonder whether it happened in this particular case because of nature of your particular DTC.

If the car in question is the vehicle in your other thread, the DTC related to the Oxygen (Lambda) Sensor and more importantly the fault status was reported as "Intermittent - Not Confirmed".

This being so, a reasonable working hypothesis might be that the sensor simply flipped-back into operational mode after resetting the errors (coincidentally - not related to the error reset) and the vehicle response felt better - maybe, I'm guessing of course?

Don
Hi Don, no it’s not related to the sensor. Even when there have been no fault codes for a week and you clear the fault codes, there is definite improvement. I did wonder if it was psycho, but from lots of googling it seems quite regular, so not just me!

Thanks, Kris
 
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Uwe

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Simple answer to the OP question: When you clear fault codes, your ECU resets the fuel trims to 0.

-Uwe-
 
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Jack@European_Parts

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Simple answer to the OP question: When you clear fault codes, your ECU resets the fuel trims to 0.

-Uwe-
Did you know that isn't always the case though & why sometimes several resets or manual clear of adaption or even rebooted ECU is required?

Granted the OP is in the UK, however, this what I see here, so I have to question the intent of madness!

Did you know resetting the fault memory is not a qualified repair and why auto-parts stores or service centers were fined heavy across Country when people did it to keep a car driving when it did not comport, same for NYS inspection before a DCY achieved for readiness?

Did you know here it is illegal to just hook up and clear codes if a consumer asks this?
 
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Uwe

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Did you know here it is illegal to just hook up and clear codes if a consumer asks this?
Maybe for a shop, in Nazi York State?

If you're claiming this is illegal on the federal level, or where the OP is (in the UK), please provide evidence in the form of a link to the relevant laws or regulations.

-Uwe-
 
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Jack@European_Parts

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Maybe for a shop, in Nazi York State?

If you're claiming this is illegal on the federal level, or where the OP is (in the UK), please provide evidence in the form of a link to the relevant laws or regulations.

-Uwe-


Did you know it is on a Federal level and why EPA and CARB fined auto part stores for it under Title CFR 40 CAA ?

Example: Autozone

In the UK I'm unsure, probably easy to tell if it is a violation of MOT right or most likely is by searching UK reg?
 
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Uwe

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That's not a citation of the actual law or regulation. I'd like to read the exact working, 'cause if it exists at all, I'm confident it applies to workshops, not to individuals working on their own cars, and I'd like to know under what conditions it applies to workshops.

But we digress. The OP asked why his engine runs differently after he clears faults, and the answer is: Clearing faults resets the fuel trims.

-Uwe-
 
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kpm

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Simple answer to the OP question: When you clear fault codes, your ECU resets the fuel trims to 0.

-Uwe-
Thanks! So with no fuel trim my car will run factory map and it might run a little too rich or a little too lean. If my car runs better on factory map, the assumption is that somewhere a sensor is contributing to an erroneous fuel trim as the car “learns”. I’ll sort out the auto scan, read the guides and start looking at measuring blocks.
 
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Jack@European_Parts

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That's not a citation of the actual law or regulation. I'd like to read the exact working, 'cause if it exists at all, I'm confident it applies to workshops, not to individuals working on their own cars, and I'd like to know under what conditions it applies to workshops.

But we digress. The OP asked why his engine runs differently after he clears faults, and the answer is: Clearing faults resets the fuel trims.

-Uwe-
Okay okay did you know you compel me to look it up when I get a chance? :p

Not quite there yet.......searching final rules but fun reading anyway.

https://www.govinfo.gov/content/pkg/FR-2001-04-05/pdf/01-8276.pdf

However, the Agencyadvises areas adopting back-up testingto address the readiness issue that theyneed to monitor the frequency of suchback-up testing to ensure that motoristsare not purposefully clearing codesprior to testing in an attempt to avoidthe OBD–I/M inspection.
https://nepis.epa.gov/Exe/ZyPDF.cgi/P1002KRN.PDF?Dockey=P1002KRN.PDF

A fraudulent attempt to avoid I/M program requirements by clearing OBD codes justprior to OBD-I/M testing (by, for example, temporarily disconnecting the battery).
 
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kpm

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I know in the U.K. that if the CEL is illuminated it is an automatic MOT failure. I had a google check for if it’s illegal for a trader to just reset but could not find an answer. I did see that one of our high street service centres suggests it can just carry out a fault code clear.

“ Please Note: Kwik Fit Plus offers a free diagnostics check when you book online. Additional charges may apply in centre for extra items & services including, but not limited to, service light reset, clearing fault codes or providing a fault code report.”
 
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Uwe

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I know in the U.K. that if the CEL is illuminated it is an automatic MOT failure. I had a google check for if it’s illegal for a trader to just reset but could not find an answer.
This is why Readiness is also checked during an I/M test in the US (in those places where such testing is required). If you clear engine faults, Readiness bits should read "Failed or Incomplete" until the ECU has had a chance to run the relevant tests.

-Uwe-
 
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Jack@European_Parts

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This is why Readiness is also checked during an I/M test in the US (in those places where such testing is required). If you clear engine faults, Readiness bits should read "Failed or Incomplete" until the ECU has had a chance to run the relevant tests.

-Uwe-
And when shows ready after such aforementioned reset, implications of FOD are suspected for tests which are impossible without a DCY required!
 
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Jack@European_Parts

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Does RTFB instruct to clear codes before a diagnosis and repair?

https://www.law.cornell.edu/cfr/text/40/86.010-38


Based on aforementioned link, does it indeed mean the OEM is on hook for decarbonization of every vehicle, unless they have approval as a maintenance requirement to comport and on file with administrator? :p

Looks like more useful life fun to come to a theater near you!
 
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