Standard wisdom: disconnecting the battery overnight on a '97-'01 XJ resets the PCM.
Here's what I'm running into: either I don't have or can't find anything from Chrysler that definitively supports this assertion.
What sparked all of this: a few months back I did the 0280155917 injector upgrade, replacing spark plugs and the throttle body gasket at the same time. Took the XJ out for a short (10-15 mile) test run to let everything bed in. Came home, unplugged the battery overnight, and the PCM presumably reset itself.
Over the next couple of weeks, I saw an improvement of around 0.5mpg which has held steady since then. Definitely better, but not quite what I was expecting. Some poking around over the next few weeks turned up a flaky oxygen sensor; new ones plus a MAP sensor (being replaced due to age, not overt failure) are on their way. Once they're in, I'd like to clear the PCM and have it be learning with the full gamut of new equipment in there.
So, my question: is there any definitive reference that states that a PCM reset can be achieved by disconnecting the battery? I'm not arguing that this isn't necessarily the correct method, just that I'd be interested to know where the idea comes from. Also, if it's possible to check with an OBD-II scantool for a reset in the PCM's stored history anywhere I'd very much like to know if that's possible.
Here's what I'm running into: either I don't have or can't find anything from Chrysler that definitively supports this assertion.
What sparked all of this: a few months back I did the 0280155917 injector upgrade, replacing spark plugs and the throttle body gasket at the same time. Took the XJ out for a short (10-15 mile) test run to let everything bed in. Came home, unplugged the battery overnight, and the PCM presumably reset itself.
Over the next couple of weeks, I saw an improvement of around 0.5mpg which has held steady since then. Definitely better, but not quite what I was expecting. Some poking around over the next few weeks turned up a flaky oxygen sensor; new ones plus a MAP sensor (being replaced due to age, not overt failure) are on their way. Once they're in, I'd like to clear the PCM and have it be learning with the full gamut of new equipment in there.
So, my question: is there any definitive reference that states that a PCM reset can be achieved by disconnecting the battery? I'm not arguing that this isn't necessarily the correct method, just that I'd be interested to know where the idea comes from. Also, if it's possible to check with an OBD-II scantool for a reset in the PCM's stored history anywhere I'd very much like to know if that's possible.