Did a hard reset after installing a new fuel rail pressure sensor and found the long term fuel trims defaulting to a steady 19.4 while the short terms are falling down to a 5 to 8 range after being high at first. I have only driven a short distance but the long term trims are not budging. How long should it take for them to come down to an acceptable level, assuming there are no issues. If they don't budge, then I guess I have either a vacuum leak or fuel supply issue.

 

If they're like that maybe they aren't wanting to go lower... go fault finding.

 

Can somebody explain to me how a so called "hard reset" changes any adaptive values in a non volatile memory.
l don't believe it does despite what now seems to be folk law.

 

“hard reset” is the lazy way to reset the KAM in the ECM. mixture adaptation is one of the things that get cleared

long terms off idle aren’t changing because he didn’t fix anything

 

DTC's and adaptive values are stored in non-volatile memory since the change to AJ27 so how does power cut clear them?
l don't think it does, that's why there is no change.

 

Thanks for the input. I did go fault finding which is why I replaced the fuel rail pressure regulator (originally had a P0193) only to have the fuel trims suddenly go up whereas they were pretty normal before replacing the fuel pressure sensor, as were the short terms. TBH, the car runs like a champ, starts right up and pulls like a train with no hesitation or stumbles now, as well as idles nicely. I tried to clear the ECU of stored fault codes as the car is running well so I thought it was just spewing up old stored fault codes. My guess is there's a vacuum leak somewhere. Will look into it further.

 

You are mis-quoting it. "DTC's and system adaptions" values, these refer to the options fitted to the vehicle such as power mirrors/seat memory/navigation/security etc.that must not be lost.
The fuel trims and other variable configurations/values are stil stored in volatile memory. I have a 2004 XKR and if I do a hard reset my fuel trims are also reset.

Interestingly if the battery is removed for a period of time the 6HP26 transmission adaptions are also reset.

If you still don't believe it and want to prove it, just do a hard reset and see what happens.

 

Hi Stumpy, my experience with a hard reset is just as you said. My fuel trims were reset to zero but jumped up to 19 after a few runs around the neighborhood. The other settings such as seat settings were not lost. I fixed the original problem (faulty fuel rail pressure sensor) only to be faced with some lean codes (both banks). Time for more troubleshooting!

 

These screen shots are from jaguar training literature, they seem to disagree. AJ26 volatile, AJ27 non volatile.
ECM's, nothing to do with seats and mirrors etc.

 

As stated by dogsoup post #8 above his trims are reset !

OK you carry on believing the training manual and ignore the people who have actual experience of these sytems and are trying to inform others of what actually happens. END

 

Regardless of those screen shots, whether misleading or wrong, fuel trims (& other things) are reset with a "hard reset" (battery disconnection) precisely as already posted because they're in KAM (keep-alive memory i.e. needs power).

 

op doesn’t have an aj27 he has a 34 🤷‍♂️🤷‍♂️🤷‍♂️ mixture adapts reset when you leave the battery out dtcs don’t

 

As l have discovered after some further research. It appears AJ27 is odd one out, might be helpful to have that known re hard reset info.