The reset procedure is billed as a ‘cheap fix’. It does often give good
immediate results, however if there is something wrong with your car then over a 2-8 week period the
car will likely return to its original state.
The reset procedure
removes all mean values stored by your onboard computer that control
engine timing, fuel use etc. As you continue to drive the car, the
stored values ‘average out’ to best suit the engine condition.
your car has for example a leaking intake manifold gasket or broken O2
sensors, the readings are quickly going to become ‘corrupted’ with
This can lead to the engine running too rich or
too lean (check your sparks for evidence). Within a short period of
time the car will return to rough idle as the underlying problem has
not been fixed.
That said – the reset procedure can reset values that
are no longer applicable. You may have replaced something on the car
(e.g. Catalytic Converters) thus causing a sudden change in normal
engine running. The readings stored over 10-20 years will suddenly not
suit you recently modified car. The car will however read new values in
and average out over time. The Reset procedure simply speeds that
The long and short of it is that this procedure can
sometimes fix rough idle and transmission timing and seems to improve
the cars performance. However with existing underlying issues as
outlined above – it won’t be long before the problems return. Perhaps
this procedure could be used if you’re trying to sell your E32 ;-)
1. Disconnect battery cables, first negative, then positive.
2. Cover and protect the battery posts! Leave no potential of a battery short circuit.
3. Turn ignition to position II.
Connect both battery cables ("SHORT") for at least 10 minutes. This
step drains a capacitor in the ECU/TCU. (Covered the battery with a
thick, dry shop towel to prevent actually shorting the battery! –
careful of arc welding the back seat! As the battery is still in place,
and the cables aren't that long, you could use a very long Craftsman
screwdriver and two small vice-grips to actually clamp the negative and
positive cables to the metal shank of the screwdriver.
5. Wait 10 minutes - then ignition off, key out.
6. Reconnect battery positive, then negative.
7. OBC says "PPPP", reset time.
Start and idle the engine for 5 minutes, then off for five, then out for a drive.
Now, with the car in lowest gear (one or two depending on your make),
accelerate until at least 5000 rpm is reached. Allow the car to slow to
idle, and then repeat two more times. Let the car idle for 5 minutes.
9. Idle should smooth out over 10-12 miles; shifts should be immediately smoother.
Thanks, Shogun... I would have never thought...
something as simple as a "reboot" would have fixed my
problems, but I gotta tell you - black magic or not - the "full
reset"-procedure worked wonders for my car!
I pulled the battery
cables, - then +, ignition to pos II, 'shorted' the battery cables
(using a loooong Craftsman screwdriver and 2 sets of vice-grips - yes,
battery posts were well isolated. No arc welding in my back seat!). Ten
minutes later, ignition off, reconnect + then -, PPPP on OBC, reset
clock. Ran the car 5 minutes, then shut down for 5.
I can't find
the words to explain the difference. I don't know if this simple act
could have made this big of a difference. But first, some anecdotal
My car always ran well. It had a bit of a lumpy idle, but
pulled smoothly and strongly off idle, and had good power. The shifts
were another story - at light throttle applications, the shifts would
seem to be a bit 'jerky'; with hesitation on downshifts (unless I
stepped down hard on the pedal) and a definitely noticable 'light
thump' after 1-2 seconds at 50-52 mph (torque converter lockup?).
Oh yeah, no stored fault codes via stomp test.
nothing unnerving - just aggravating. Trans fluid level good, color and
fluid visual quality good. I cleaned the trans selector switch (it
wasn't too bad), I had considered a full tranny flush (I've heard all
of the banter on the board, pro and con); I had checked the intake
system for air leaks (none), and I thought about changing out the
oxygen sensors just to see if they were the cause of the lumpy idle...
I know that we're all exceptionally sensitive to the daily behavior of
our E32s; I attributed a lot of these 'issues' to the fact that it is a
14-year old car, and I forced myself to just enjoy it. It was tough at
times; I knew that this car should run exquisitely, not just well.
- I changed NOTHING between Monday evening and Tuesday morning, other
than the 'reset'. Temp was nearly the same (maybe five degrees F
cooler), clear, moderate humidity. Fuel level the same.
the 1st drive, post-reset. After an immediate start, the idle seemed to
be improved - just a bit. Still a lump or two... but it could be
smoother - maybe? Peak-to-peak amplitude of the 'lumps' seemed to be
reduced. Selected reverse, waited for the light clunk - none! Ok, this
Released the brake, backed out of the garage. Is
the throttle more progressive? Seems that the driveline is tighter; am
I imagining this? Out into the street; drove my daughter to the high
school, four miles down the road. Pulled onto a 4 lane, 50mph section
of road and stepped down. Oh, man - what a difference - 1-2 shift was
not perceptible, 2-3 shift was silent. 3-4 shift was... did it happen?
I guess - the tach was at 1900, speed 52. What shifts?
I didn't feel any shifts!
took it easy the rest of the way in to work - mostly city driving with
an average speed of 40-45mph. Pulled into the garage at work, selected
park, opened the door and stepped out with the engine running... or,
Rock solid, smooth idle. No lumps, no bumps. The car
downright SOUNDS different at all speeds, including idle! I shut it off
and restarted. Instant start, rock solid idle. I mean ROCK SOLID - one
of those is-it-running? idles. This car has NEVER done this before.
I'm amazed - but I'm also frustrated...
a mechanical engineer working for 20 years in the software business, I
appreciate the value of a well-earned reboot - but, is it possible that
this simple action could have made this much of a difference in the
I understand that the Motronic ECU is adaptive -
but, of course, not near as adaptive as today's OBC II+ technologies.
What's more interesting is the transmission's behavior. I thought for
sure that I was going to be hailing Kurt K soon - and now, my trans has
miracuously healed itself (!) - it has never been this smooth in the
two years I've owned this car.
Is the trans control unit also adaptive? Could this actually be real?
I still in bed, dreaming? I've had the battery disconnected a dozen
times before, often for longer than an hour - but I never did the
'short' thing with the battery cables... Shogun, somebody's on to
something - believe it or not!
Whatever. Try it. Could be the best 10 minutes you ever spent.
I'd love to hear from anyone who can concur as to the efficacy of this simple 'reset'.
-Mr. Smooth Idle!
Don Strimbu -
Bartlett, IL USA - BMWCCA #311395
1990 735i - 69,800 miles
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