Resetting the ECU

[Theothertyler]

Hey everyone-

I've come across a few posts dealing with resetting the ECU, but having driven an older car for so long I really have very little idea what it actually does.

3 questions:

What does the ECU specifically control, in terms of actual engine mechanics and observable results? I've heard that mpg can go up depending on driving style, and I just put new bigger tires on so my engine will have more to adjust to now.

Would you recommend resetting the ECU on a vehicle you just purchased used?

How do I go about resetting it on a 4th gen? I've heard of people just disconnecting the -- terminal but it seems like there has to be a more technologically-savvy way of doing it! (Like disconnecting a wire or fuse, so that you don't have to reset everything)

Thanks in advance for the input -

:cheers:

 

[eskimochaos]

Disconnecting the battery is the only way I believe, 10mins or so and your good to go. Dont be surprised if you start it and it stalls immediately - the car has to relearn basically everything.

I believe you have the 4speed transmission in your 04 V6 which does not feature intelligent shifting/artificial intelligence so there will be no change there.

 

[toto]

The truck actually has many ECU's. ECU, or electronic contol unit, is the auto industry's term for "computer". If something has automated features in it, then there's an ECU somewhere to control it.

Some of the ECU's are desgined to "learn" how you drive or to retain data about past history and alter their behavior accordingly. The two that people usually want to reset are the engine control ECU and the transmission ECU. Both of those keep data for various reasons, and resetting them by cutting the power and wiping out their memory gets them to start back at the original settings. The learning function is often intended to optimize gas mileage (for things like air/fuel ratio or trans shifting), and the engine ECU also stores diagnostic information.

It's not necessary to make a habit of resetting them, and they're really not meant to be reset regularly. That's why the only way to do it is to disconnect the battery.

 

[Annoyed]

Just don't forget that you will have to reset the power windows, tailgate window, sunroof, and other things as well.

 

[toto]

Good point! The instructions for the resets are in this thread.

 

[denzel.ahquin]

quick question

I'm about to install a cool air flow intake kit for my 1994 4runner. Am I supposed to reset the ECU at the end? If so, please explain the steps. Thanks in advance

 

[DisguisedRope]

I'm about to install a cool air flow intake kit for my 1994 4runner. Am I supposed to reset the ECU at the end? If so, please explain the steps. Thanks in advance

You might have better luck asking on this part of the forum

 

[denzel.ahquin]

thank u! much appreciated

 

[BlackWorksInc]

If you have a TIS Techstream you can erase the modules stored values without disconnecting the battery.

 

[ChucktownRunner]

The truck actually has many ECU's. ECU, or electronic contol unit, is the auto industry's term for "computer". If something has automated features in it, then there's an ECU somewhere to control it.

Some of the ECU's are desgined to "learn" how you drive or to retain data about past history and alter their behavior accordingly. The two that people usually want to reset are the engine control ECU and the transmission ECU. Both of those keep data for various reasons, and resetting them by cutting the power and wiping out their memory gets them to start back at the original settings. The learning function is often intended to optimize gas mileage (for things like air/fuel ratio or trans shifting), and the engine ECU also stores diagnostic information.

It's not necessary to make a habit of resetting them, and they're really not meant to be reset regularly. That's why the only way to do it is to disconnect the battery.

I've been doing a lot of electrical work inside my car and have been continuously disconnecting/reconnecting the battery.. Was actually going to look into a possible kill switch and quick disconnect so I don't have to constantly unbolt the terminals.. Is it bad for me to constantly disconnect my battery to work on stuff? If so, how do you get around not disconnecting the battery?

 

[BlackWorksInc]

I've been doing a lot of electrical work inside my car and have been continuously disconnecting/reconnecting the battery.. Was actually going to look into a possible kill switch and quick disconnect so I don't have to constantly unbolt the terminals.. Is it bad for me to constantly disconnect my battery to work on stuff? If so, how do you get around not disconnecting the battery?

It shouldn't hurt anything to disconnect them and reconnect them as the only thing getting erased should be the non-critical memory.

As for your second question, not really as power is supplied to multiple systems on multiple lines, you're theoretical cut-off would have to take that into account and at that point you're still better off disconnecting the battery at that point.

 

[ChucktownRunner]

It shouldn't hurt anything to disconnect them and reconnect them as the only thing getting erased should be the non-critical memory.

As for your second question, not really as power is supplied to multiple systems on multiple lines, you're theoretical cut-off would have to take that into account and at that point you're still better off disconnecting the battery at that point.

Thank you sir!

 

[ricofreako]

Which ECU would be probable cause for car not being able to start?

 

[BlackWorksInc]

Which ECU would be probable cause for car not being able to start?

What do you mean?

There's lots of reasons a vehicle could not be starting and some that could be related to the ECM/PCM (Engine Control Module/PowerTrain Control Module, depending on what functions it does).

If you mean from a security standpoint, that would be the handshake between the ECM/PCM and Immobilizer module. So in that case it could be the ECM/PCM, the Immobilizer, or both.

 

[97hb]

Which ECU would be probable cause for car not being able to start?

Any ECU that controls throttle plate or DBW. It needs to re-learn the idle speed. My idle is rock solid 700rpm, when I reset the ecu it goes down to 500rpm for a while till it re-learns. Mine has never died though. My OBD2 monitor shows about 14% open at idle normally. When I reset the ecu it goes down to 10% till it re-learns the idle speed.