How to: Reset Your ECU After Any Performance Modification

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BigJ

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While the manual doesn't specifically say you should do this after any mod you make, its probably a good idea. Your ECU (Electronic Control Unit, sometimes called a PCM or Program Control Module... basically the thing that controls how your engine runs) is smart; it learns over time how to adjust itself to get best performance and economy, taking into account lots of things, including your driving style, habits, specific environment, fuel type and quality etc etc. It does all this by watching and tweaking itself, then watching again for new to see how the motor is running. All this is based on input and feedback from several sensors all over the truck and drivetrain.

Sometimes when you change something (be it a new CAI, exhaust, fuel types, even environments), your ECU sees dramatically different input and feedback... aka 'stuff', for lack of a better term. It therefore needs to unlearn what its already learned about the old 'stuff', to then be able to relearn all about the new 'stuff'. You can speed this process along by resetting your ECU back to how it came from the factory. It can then start with a fresh slate, and learn your new 'stuff' right away.

NOTE: If your mod did not involve disconnecting the battery, disconnect it for 45 minutes before performing the relearn process listed below.

(If you don't clear the ECU by disconnecting the battery, I doubt the relearn would accomplish anything)
From page 372 of the 2010 F150 Owners manual:

Battery relearn
Because your vehicle’s engine is electronically controlled by a computer, some control conditions are maintained by power from the battery. When the battery is disconnected or a new battery is installed, the engine must relearn its idle and fuel trim strategy for optimum driveability and performance. Flexible fuel vehicles (FFV) must also relearn the ethanol content of the fuel for optimum driveability and performance. To begin this process:

1. With the vehicle at a complete stop, set the parking brake.

2. Put the gearshift in P (Park), turn off all accessories and start the engine.

3. Run the engine until it reaches normal operating temperature.

4. Allow the engine to idle for at least one minute.

5. Turn the A/C on and allow the engine to idle for at least one minute.

6. Release the parking brake. With your foot on the brake pedal and with the A/C on, put the vehicle in D (Drive) and allow the engine to idle for at least one minute.

7. Drive the vehicle to complete the relearning process.

• The vehicle may need to be driven 10 miles (16 km) or more to relearn the idle and fuel trim strategy along with the ethanol content for flexible fuel vehicles.

• If you do not allow the engine to relearn its idle trim, the idle quality of your vehicle may be adversely affected until the idle trim is eventually relearned.

• For flexible fuel vehicles, if you are operating on E85, you may experience poor starts or an inability to start the engine anddriveability problems
 

MarkT

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I would add a very important additional step... if your mod did not involve disconnecting the battery, disconnect it for several minutes before performing the relearn process.

(If you don't clear the ECU by disconnecting the battery, I doubt the relearn would accomplish anything)
 
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BigJ

BigJ

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I would add a very important additional step... if your mod did not involve disconnecting the battery, disconnect it for several minutes before performing the relearn process.

(If you don't clear the ECU by disconnecting the battery, I doubt the relearn would accomplish anything)
So noted in the original post. Thanks Mark!
 

FSM06

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It will take more than several minutes fellas. The KAM (or Keep Alive Memory) incorporated within the PCM (Powertrain Control Module) is where the the stored or "learned" data is stored. We have tried the battery disconnect a few times and it will take up to 45 minutes to clear the KAM. Our scan tools can accomplish this in a few seconds. If you use the battery disconnect method, I would suggest you wait at least 45 min to one hour before reconnecting the battery.

FSM
 

pat'sRAPTOR

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So I'm assuming this is for guys not running a tune like the ones from 5star? Or would this work on that too. But if the computer dumps what is learned does it dump the tune as well? Will you he to reload the tune?
 

Cleave

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I would like to know if anyone has done this and the truck actually adapted faster to any modifications other than internal engine components, since the intake air charge is not a learned parameter but one that is monitored constantly and adapted for instantaneously
 
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