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Importance of Reseting Fuel Trim (LTFT).

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This topic is in the MVS Volvo Repair Database » Importance of RESETTING Fuel Trim (LTFT)
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Re: Importance of Reseting Fuel Trim (LTFT).

Post by optowalt »

Thanks for the info. So far it's working. I'll know after a week or so. You guys are great. Walt

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Post by zoomungus »

I have 3 ecu's, 2 standard and 1 remap and after having worked or fixed anything on the engine I replace the ecu, I also let the car totally get to operating temp before driving with the fresh ecu.

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Post by tom39 »

Would this or could this be the reason for a code of P0422, main catalyst efficiency for bank 1 is below threshold?
If so this would be awesome

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Post by diplomat128 »

Is this only for S70's or does this apply to other cars, let's say an S80 T6?

Would this help my car "reset" after my new MAF and ETM cleaning?

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Post by Brucebo »

diplomat128 wrote:Is this only for S70's or does this apply to other cars, let's say an S80 T6?

Would this help my car "reset" after my new MAF and ETM cleaning?
It applies to all electronically controlled fuel injection vehicles, although the means of resetting the adaptive fuel trim is vehicle specific. As to these means, I can only speak for the S70.


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Post by volvoheader79295 »

OK. I just disconnected the battery to work on something else for over an hour. I reconnected it. Should I do this again, turn the start key to on, re-connect the battery after several minutes, then turn the key off? A little confused by that. ~ John

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Post by jblackburn »

Nah, should be alright, it's forgotten everything already and will have to re-learn anyway :mrgreen:
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A learning experience is one of those things that says, "You know that thing you just did? Don't do that."

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Post by flintash »

Sorry for pulling old tread back, but ....
The procedure doesn't work on my S40 T4 2001. It resets diagnostic tests, but not Fuel Trims. I'm quite in hurry cause of emmision test in next few days, so begging you to help me.

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Post by jimmy57 »

Wait guys! DO not immediately conjure up vast improvements in your car's performance from sending fuel trims back to default values. I am in no way discounting the benefits of this procedure for SOME issues. Depending on the part replaced and how biased it was before being replaced the reset to defaults can have the same effects. You may have a car that needs LTFT factors in the 1.12-1.16 range and they have gone to 1.20 +/- range. If you reset to 1.00 then you can have the same effects of improper fuel trim and momentary poor performance when you find those load/rpm windows not yet updated. If your have a lower miles and stage 0 car whose LTFT adapted will be 1.02 to 1.05 and you reset from a previous 1.20 then you will see more positive effects.
If you go outside and dance around your car thinking it will cast a spell and you then go drive expecting a change then you will see one. Especially since the weather has cooled and cars run better in cooler air with higher oxygen concentration, something they haven't had when temps were near 100F.
What is absolutely true is that any issue causing fuel trims to go down to .80-.85 can cause hesitation and "dead" spots for a time since low factors lean the mixture until corrected for.

I am not poo-pooing on Bruce's post, I just want you to have real expectations. Good techs usually clear fuel trims on purpose after repairs. What also has happened in a LOT of instances is that battery gets disconnected as part of a repair and the owner drives off and comes back and complains car runs worse after you replaced my starter, etc., that has no bearing on the fuel system. Clearing fuel trim via batt disconnect in these cases set an adapted car back to default values and until a seasoned car runs for a time in various speed/load ranges it suffers consequences.

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Post by flintash »

Well, I kinda agree with you, but I had a car running for VERY long time with vacuum leak,so i fixed this and on top of that I cleaned MAF and replaced O2 sensor. I believe car is in need of LTFT reset. So please, tell me how, cause disconecting battery, pressing brakes, draining through starter doesn't work on Volvo S40 T4 2001 !

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