Reseting VN-VP ECU

[VN_chris]

I have searched the forum and asked the question a couple of times but no one seems to agree on how to reset/ clear the memory of a VN-VP ECU. whats the right way?

[needwork2-4fillhabbit]

Warm your car up to running temps, then pull the leads off your battery. Wait for a few minutes while you drink a beer, replace the leads and start your car, hold revs at 2-2500k then its all reset and redone. 1500k revs might be be all that is needed but i usually do 2500 cos i like the sound.

[Not_An_Abba_Fan]

It's not really necessary to warm the car up. Just the positive battery terminal disconnected for 10 seconds will reset the ECU. The revving to 2000 rpm resets the TPS.

[azzfox]

Just pull the main engine fuse. Saves losing radio presets.etc and you dont have to reach for your trusty 10mm spanner. Then just hold it at throttle until the revs stabilise.

[Karsten]

It's not really necessary to warm the car up. Just the positive battery terminal disconnected for 10 seconds will reset the ECU. The revving to 2000 rpm resets the TPS.

what does TPS stand for? and isnt it better not to give the car any acceleration and just let it idle for 5 minutes? because its telling the computer to put to much fuel in when holding it a 2K Revs?

[HICOMPVN]

dude, tps stands for "throttle position switch", no cos if you have changed anything it needs to be recalibrated, it recognises that your holding the trottle at 2k and resets it'self (tps)from there!!!!

[Cheap6]

The ECM memory is continually overwritten - aka self learning - so really you have to do nothing other than drive the car to "reset" the ECM. Even fault codes will clear after 20 engine starts - actually ECM power ups i.e. key on to "reds" - if the conditions to trigger one are no longer present.

Disconnecting battery power from the ECM for greater than 10 seconds will clear the ECM memory and revert the "learned" values to the factory defaults. Removing a battery terminal can achieve this as can removing the "ENG COMP" fusible link. The fusible link is under the bonnet in front of the relay box (behind the battery) with its position labelled on the cover over the fusible links.

If power to the ECM is removed the ECM will have to relearn the position of the Idle Air Control (IAC) motor. This happens when engine revs first go above 2000rpm after a key off of > 10 seconds (subsequent to power being disconnected from the ECM). When this occurs the ECM will drive the IAC motor "closed" for long enough to be sure that it will in fact be closed, regardless of its starting position. This gives an IAC reference position for the ECM to use. The > 2000 rpm requirement can be achieved just as easily during normal driving as it can by revving the engine in neutral.

The ECM will also need to learn "first guess" positions for the IAC at idle in the two or four combinations available with A/C on/off and in drive/neutral (if applicable). This will be completed with the engine up to operating temp. and may result in some variation in idle speed as it occurs.

In summary, a forced ECM reset is not often necessary. About the only reason to do so being a quick confirmation that a repair causing a fault code to occur has been successful. Otherwise, just drive the car, especially since some parts of the fuel mixture map are seldom seen in normal driving and take ages to relearn if they are cleared.

The (closed) TPS position is "learned" by the ECM at each start.

[91vn]

Take the terminals oof the battery wait 1 hr then re connect. should doi it worked for my vy

[jdodd]

Take the terminals oof the battery wait 1 hr then re connect. should doi it worked for my vy

a minute is all it needs

[Doctor Bob]

get the engine to operating temperature
remove the engine fuse for 20 seconds,
restart & hold the revs above 2500 for 10 seconds to reset the IAC

the TPS zero reset is only from VT & later

[Cheap6]

get the engine to operating temperature
remove the engine fuse for 20 seconds,
restart & hold the revs above 2500 for 10 seconds to reset the IAC

the TPS zero reset is only from VT & later

That's a very practical way of achieving the greater than 10 seconds and 2000rpm requirements. It's still questionable as to why it is necessary at all.

Yes, VT- will relearn TPS idle position any time that idle occurs. Where no adjustment for TPS position is present, as for VN- , the TPS 0% position will be learned by the ECM/PCM at least on start up.

[Doctor Bob]

That's a very practical way of achieving the greater than 10 seconds and 2000rpm requirements. It's still questionable as to why it is necessary at all.

Yes, VT- will relearn TPS idle position any time that idle occurs. Where no adjustment for TPS position is present, as for VN- , the TPS 0% position will be learned by the ECM/PCM at least on start up.

The 20 seconds is to allow the ECM to power down completely
the revs need to be held up until the IACV resets
VT relearns the TPS at ignition on
VN- does not at any time

[Cheap6]

VT relearns the TPS at ignition on
VN- does not at any time

I went back to the engine management workshop manuals for a couple of models using the 1227808 to be sure I wasn't misremembering something. In the TPS output check and under the two fault codes for the TPS is: "The TPS is not adjustable. The ECM uses the reading at idle as "0% throttle", so no adjustment is necessary."

From a VT series mass air flow manual: "The PCM will learn what the closed throttle value is every time the throttle comes back to closed throttle.". I can't say with the same certainty what VR and VS do but they should do what VN/VP and VT do respectively. GM is not lone in non-adjustable TPS, self-learning ECM either.

The learning makes sense as, apart from manufacturing variation between TPS's and throttle bodies, base idle speed adjustment will alter the TPS signal voltage at idle. I suspect the learning each time the throttle is closed, as distinct from only on key on/start, is to avoid stalling caused by intermittent sticking of the throttle varying the apparent base idle speed and the corresponding IAC motor steps needed to reach the desired idle speed prior to feedback correction.

Fair comment re. having the revs above 2000rpm for long enough for the IAC valve to close. I still say just drive the car.

Interestingly, in looking up the TPS info., I also found that an IAC reset can also be forced on the 1227808 (VN-VP) by inserting a 10k ohm resistor across terminals 'A' and 'B' on the ALDL connector. These are the same terminals that are shorted with a jumper wire to extract the codes by flashing the check engine light on the dash - a 10k ohm resistance is what Tech 1 uses to indicate to the ECM that it is connected to the ALDL. The > 2000rpm bit is still required.

[immortality]

yes cheap6, driving the car will eventually cause it to re-learn the idle, however doing the tried and tested method of dis-connecting the ecu for 20 seconds and then holding the revs @ 2000rpm forces the ecu into a reset and you know it's then set.

on occasion when i've been in a hurry after re-fitting the the TB and haven't done a full reset and just driven off i've encountered stalling/high revs at idle issues as the PCM tries to relearn. doing a forced reset negates these problems.

[Doctor Bob]

From a VT series mass air flow manual: "The PCM will learn what the closed throttle value is every time the throttle comes back to closed throttle.". I can't say with the same certainty what VR and VS do but they should do what VN/VP and VT do respectively. GM is not lone in non-adjustable TPS, self-learning ECM either..

The VT system will learn the MAF value at 0% TPS, the TPS value is done at power down

[PietroChocko]

I think cheap6 nailed it.