How to Perform a Throttle Relearn on Your Lexus Vehicle

If you’ve recently disconnected the battery, cleaned the throttle body, or replaced the throttle position sensor on your Lexus, you may need to perform a throttle relearn procedure. This process allows the engine control module (ECM) to relearn the idle and throttle settings.

Performing a throttle relearn is important to ensure your Lexus idles smoothly and accelerates properly. Without doing this, you may experience rough idling, stalling, hesitation on acceleration, or a check engine light.

Lexus Models That Require a Throttle Relearn

The throttle relearn procedure applies to many Lexus models from the early 2000s through today, including:

Lexus IS 250/350 (2006-2013)
Lexus ES 330/350 (2004-2012)
Lexus GS 300/350/430/460 (2006-2011)
Lexus LS 430/460 (2001-2012)
Lexus RX 330/350/400h (2004-2009)
Lexus GX 470 (2003-2009)
Lexus LX 470/570 (2008-2011)

If you have one of these Lexus models and have recently disconnected the battery or cleaned the throttle body, follow the steps below to perform a throttle relearn.

Throttle Relearn Procedure for Lexus Vehicles

Before starting, make sure the vehicle is parked on a level surface, the parking brake is engaged, and the gear selector is in Park or Neutral. Do not press the accelerator pedal during this process.

Step 1: Warm Up the Engine

Start the engine and let it idle until it reaches normal operating temperature. You can check this by looking at the temperature gauge on the instrument cluster – it should be in the middle.

Step 2: Turn Off All Accessories

Turn off the air conditioning, radio, headlights, and any other accessories that may be on. This ensures there is no extra load on the engine during the relearn process.

Step 3: Turn the Key to the On Position

Turn the ignition key to the “On” position but do not start the engine. Wait a few seconds until you hear the fuel pump prime (a faint humming noise).

Step 4: Turn the Key Off

Turn the key back to the “Off” position. Wait 10 seconds.

Step 5: Repeat Key Cycles

Repeat steps 3 and 4 one more time. This means turning the key to “On”, waiting a few seconds, then turning it “Off” and waiting 10 seconds.

Step 6: Start the Engine

After the second key cycle, start the engine. It should start up and run normally. If the check engine light was on before, it should turn off after a few drive cycles if the relearn was successful.

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Step 7: Let the Engine Idle in Drive

With your foot on the brake pedal, shift the transmission into Drive. Continue holding the brake and let the engine idle for about 5 minutes. You may notice the idle speed change as the ECM relearns the idle settings.

Step 8: Shift to Park and Turn Off Engine

After 5 minutes, shift the transmission back into Park and turn off the engine. The throttle relearn procedure is now complete.

Tips for a Successful Throttle Relearn

Make sure the battery is fully charged before starting. A weak battery can cause issues during the relearn process.
Do not touch the accelerator pedal at all during the relearn. Any throttle input can confuse the ECM.
If the engine stalls or runs roughly during the 5-minute idle period, turn it off and start the procedure over from the beginning. It may take a couple of tries to get it right.
In some cases, you may need a scan tool to fully complete the relearn process. If the steps above don’t work, consult a professional mechanic who has a compatible scan tool for your Lexus model.
After performing a throttle relearn, it’s a good idea to take your Lexus for a test drive. Drive it gently at first, then try some light acceleration and deceleration. The ECM will continue to fine-tune the settings as you drive.

Why is a Throttle Relearn Necessary?

The throttle body is the part of the engine that controls the amount of air entering the intake manifold. It contains a throttle plate that opens and closes to regulate airflow. The throttle position sensor (TPS) monitors the position of the throttle plate and sends a signal to the ECM.

Over time, carbon deposits can build up on the throttle plate and affect its operation. Cleaning the throttle body periodically helps remove these deposits and maintain proper airflow. However, disconnecting the throttle body or TPS during cleaning causes the ECM to lose its learned settings.

The battery provides power to the ECM to maintain its memory. If the battery dies or is disconnected, the ECM will also lose its memory and revert to default settings. This can cause drivability issues until the proper settings are relearned.

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Performing a throttle relearn procedure communicates to the ECM that the throttle body and TPS have been reinstalled or that power has been restored. It allows the ECM to recalibrate the idle speed and throttle response to the current conditions.

Common Symptoms of a Throttle Relearn Issue

If your Lexus is experiencing any of the following symptoms, it may need a throttle relearn:

Rough idle: The engine may idle too low, too high, or fluctuate rapidly. You may also feel vibrations inside the cabin.
Stalling: The engine may stall when coming to a stop or when the throttle is quickly pressed and released. This is often accompanied by rough idling.
Hesitation on acceleration: When you press the accelerator pedal, there may be a long pause before the engine responds and begins to accelerate. It may feel like the car is “thinking” before it moves.
Surging: The engine speed may suddenly increase and decrease for no apparent reason, especially when cruising at a steady speed. This can feel like the car is lurching forward and backward.
Check Engine Light: The check engine light may come on and store a trouble code related to the throttle system. Common codes include P0120 (Throttle Position Sensor Circuit Malfunction) and P0121 (Throttle Position Sensor Range/Performance Problem).

If you notice any of these issues after disconnecting the battery or cleaning the throttle body, perform a throttle relearn procedure as described above. In most cases, this will resolve the problem and restore normal operation.

Preventing Throttle Relearn Issues

To avoid the need for a throttle relearn in the future, follow these tips:

Disconnect the negative battery cable before servicing the throttle body or TPS. This will prevent the ECM from losing its memory and settings.
Clean the throttle body regularly. Over time, carbon deposits can build up on the throttle plate and affect airflow. Cleaning the throttle body every 50,000 miles or as needed can help maintain optimal performance.
Use a memory saver when disconnecting the battery. If you need to disconnect the battery for any reason, use a memory saver device to maintain power to the ECM. This will prevent it from losing its learned settings.
Address any check engine lights promptly. If the check engine light comes on and stores a code related to the throttle system, have it diagnosed and repaired as soon as possible. Ignoring the problem can lead to further damage and more expensive repairs down the road.

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When to See a Professional

While the throttle relearn procedure is relatively simple and can be done at home, there are some cases where it’s best to see a professional mechanic:

- The relearn procedure doesn’t work after multiple attempts. If you’ve followed the steps carefully and the engine still runs poorly, there may be an underlying issue that needs to be addressed.
- You don’t feel comfortable working on your own vehicle. If you’re not familiar with basic automotive maintenance or don’t have the proper tools, it’s best to leave the job to a trained technician.
- Your Lexus is still under warranty. If your vehicle is covered by a factory or extended warranty, it’s best to have any repairs or maintenance done at an authorized Lexus dealership. Attempting repairs yourself could void the warranty.

You suspect there may be other issues besides the throttle system. If your Lexus is experiencing problems that seem unrelated to the throttle, such as misfires, poor fuel economy, or strange noises, a professional diagnosis is recommended. There could be multiple issues at play.

Conclusion

Performing a throttle relearn procedure is an important step after disconnecting the battery, cleaning the throttle body, or replacing the throttle position sensor on your Lexus. It allows the engine control module to recalibrate the idle speed and throttle response for optimal performance.

Key Takeaways

A throttle relearn procedure is necessary after disconnecting the battery, cleaning the throttle body, or replacing the throttle position sensor on a Lexus vehicle.
The procedure allows the engine control module (ECM) to recalibrate the idle speed and throttle response.
Symptoms of a throttle relearn issue include rough idle, stalling, hesitation on acceleration, surging, and a check engine light.
The throttle relearn procedure can be done at home using the ignition key and following a specific sequence of steps.
Regular maintenance and using a memory saver when disconnecting the battery can help prevent the need for a throttle relearn.
If the procedure doesn’t work after multiple attempts or there are other suspected issues, it’s best to consult a professional Lexus technician.