Hard reset of fuel trims

[EddieRiff]

Resetting of fuel trims:

I did all of the regular tricks, to no avail I unplugged battery, discharged, reset dtc's, touched unplugged battery terminals and still my ltft still show 13% when urban driving and as soon as I get on the motorway, especially uphill it rises to about 19% I back of and take it easy so-to-speak and it drips down to 15/16% again. Stft fluctuates -6+/-4+ all from zero.
I'm still none-the-wiser. Any ideas?

Volvo 2003 S40 1.8: B4184S2 engine petrol.

[solo99]

Hi Eddie. I'm in the same boat. Not replies to your topic, so it must be not an easy one. Did you ever figured it out?

[Vova585]

Have you considered that your fuel trims might actually be correct? Any chance you suspect vacuum leak in your car? Would be great to perform "smoke" test on it. In the recent past, any new parts or services? Have you checked coolant temp info, info from Maf?

[Struikrover]

I was able to reset my trim adaptions with the 850 OBD-II app + an ELM327. Vida with a full Dice chip (sadly Mongoose/J2534 doesn't work for us) would be another option.

That said, if trims are acting weird (outside of -10 to 10%) and it's not fixing itself then there should be a cause that requires fixing.
You can ignore it but as soon as you reset the adaptations it would in theory move (gradually) towards the problematic trims again.
Running either lean or rich both cause a variety of problems/preconditions you would rather avoid.

So long as the trims are moving and drivability is good I would, as Vova585 suggests, try to figure out what's up.
Fix the underlying problem and the trims should adapt and fix itself.


If you wonder why I did a reset on the adaptations; the LTFT of my car was stuck on 19% from the moment I bought it.
With stuck I mean the LTFT was permanently at this 19% and never registered another value.

The previous owner had ignored a P0171 (too lean) DTC for a long time - he mentioned in his notes that the DTC could show up (was pretty much permanent at this point), stating it "didn't hurt performance or was harmful", based on him driving to Poland and France without any problems.

Cause for the condition was a leak at the flex/downpipe before the o2 sensor, meaning the sensor would always register excess oxygen, resulting in the ECU interpreting a constant lean condition when there really wasn't. Something which can't be fixed by adapting the fuel/air mixture or any time passed as long as the leak is present.


Thread about the Android App:
viewtopic.php?t=83145
It's geared mostly towards other Volvo platforms but the EMS2000 is (partially) supported.