How to Reset Car Computer (9 Steps)

An onboard computer (a.k.a. Electronic Control Unit/Module or ECU/ECM) is a system that operates everything in your car, from cruise control to anti-lock braking systems. It makes a ‘mental note’ of everything related to the engine (including safety functions). But over time, your vehicle develops glitches, breakdowns, and performance flaws, causing your ECU/ECM to throw fault codes. At this point, knowing how to reset car computers becomes crucial.

A car computer reset entails disconnecting the battery, removing the fuse, and having your car relearn driving habits (among others). However, not all cars benefit from an ECU reset via a simple battery or fuse removal. If it is your first time, seek help from someone more experienced.

Conversely, here are nine simple steps on how to reset your Jeep computer (also applies to other vehicles) if you are feeling confident and up to the task:

1. Use a high-spec diagnostic scan tool.
2. Turn off your car battery.
3. Insulate the battery wires.
4. Do a soft reset.
5. Remove the ECU/ECM fuse from the fuse box.
6. Observe the 45-Minute Waiting Period.
7. Put the battery back in place.
8. Reset radio and clock presets.
9. Complete the Idle Relearn Procedure.

While the list in this article is non-exhaustive, it enumerates foolproof ways of going about a car computer reset. You may find some steps are inapplicable, as they would always depend on the year and type of vehicle you drive. In performing these steps, I recommend having your owner’s manual and a scan tool with you. Let’s dive into resetting your car’s ECU.

How to Reset Your Car Computer

1. Use a High-Spec Diagnostic Scan Tool.

If the reason for resetting your Jeep computer has to do with electronics glitches in your car, then this step is required. However, electrical problems can be tricky to diagnose as they stem from several things.

It would be best to use an advanced scan tool like Ancel V6 Pro Bidirectional Scan Tool (view on Amazon) to ascertain what is going on and whether the issue calls for an ECU reset or not. Plug the scan tool in your vehicle’s designated OBD-II port, typically found under the dashboard (driver’s side).

2. Turn Off Your Car Battery.

To do this, first, turn off your vehicle. Remove both terminals of the battery using a battery wrench and extract the battery from its compartment. This step is crucial as it ensures no power flow to your car’s electrical components while resetting the car computer or ECU (Electronic Control Unit). It also allows you to verify your battery’s integrity and see if the latter requires maintenance.

3. Insulate the Battery Wires.

Although you have removed the battery itself from its compartment, it is still wise to short the connected positive and negative wires since there is always residual current left in a vehicle’s capacitor circuit or airbag.

Tying the said wires with a cable or insulating tape will leave no room for accidentally getting electrocuted while working on resetting your Jeep computer (or whichever vehicle you have). Moreover, this trick helps drain the capacitors faster.

4. Do a Soft Reset.

After detaching the battery from the engine wiring, perform a soft reset. This process entails cutting off power flow to the ECU or car computer by draining any pending current left inside the capacitor circuit or some other electrical component.

Once the ECU is completely drained of power, it would lose any memory left in its system – hence the term ‘soft reset.’ In most cases, this step also resets Diagnostic Trouble Codes, making it a significant part of how to reset car computers.

5. Remove the ECU/ECM Fuse From the Fuse Box.

Long-time vehicle owners are split when it comes to performing this step. Some swear by this step alone, while others perform it alongside disconnecting the car battery (view on Amazon) from the compartment.

To add, there is a lot of discussion around how long the fuse should be out before placing it back in the fuse box. Whichever route you take, the important thing to note is that you should never leave the fuse out of the fuse box for too long – either 10 seconds or 15 minutes tops will do.

6. Observe the 45-Minute Waiting Period.

After steps 1–3, you will need to wait approximately 45 minutes before replacing the battery and its terminals in their original position in the battery compartment. Because you will have to wait 30 minutes to an hour, take this opportunity to clean your battery with baking soda, water, or a cleaning solution.

If you have a handheld vacuum like Black & Decker 20V Max Handheld Vacuum, Cordless Grey (view on Amazon), you might as well give your dashboard and upholstery a good clean.

7. Put the Battery Back in Place.

While at it, inspect the battery terminals for corrosion and looseness. These flaws should have already been addressed when cleaning your battery during the 45-minute wait.

8. Reset Radio and Clock Presets.

Do not forget to reset the clock and radio presets after completion of the ECU reset. Additionally, you will need to do these resets in order, with the radio being booted first. If your vehicle has a digital platform similar to Uconnect® in Jeeps, Rams, or Chryslers, you only need to deactivate GPS and remove the SD card from it. After which, press the recessed “Reset” button on the side of the LCD display and allow the unit to fully reboot.

Reactivate GPS next, and verify if the clock is correctly displayed. Depending on the vehicle or Jeep label owned, removing the multimedia fuse from the smart junction box may be warranted.

9. Complete the Idle Relearn Procedure.

For most four-wheelers, the steps below should suffice:

• (Optional) Disconnect the battery or remove your vehicle’s ECU fuse. Then let the car sit for 15 minutes to give it time to fully reset. After the period has elapsed, put back the ECU fuse or reconnect the battery.
• Make sure all electrical components are off.
• Start the car while in Neutral or Park and hold the speed at 3,000 RPM. Wait for the engine coolant temperature to reach 194° F (90° C) or for the radiator fan to come on.
• Let the vehicle reach normal operating temperature (about 5–10 minutes) with the throttle closed and all electrical components still off. Note that the time spent in doing this step should not include radiator fan run time.
• Turn the car off and on. Then, drive around for about 200 miles to allow the vehicle to relearn all the fuel maps, shift points, and conversions and complete the relearn process.

Jeeps

Jeeps, however, require a few more steps than most vehicles. Below is an example of the Idle Relearn Procedure for a Jeep Renegade (2.4-L automatic):

• Turn off all accessories.
• Turn the ignition to “ON” (Not Start).
• Wait for the “DING” before fully depressing the accelerator or throttle. Do this step until the Check Engine Light flashes.
• Hold this position until the Check Engine Light stops flashing.
• Turn the ignition key to “OFF.”
• Release the throttle.
• Wait for two minutes before starting up the vehicle.

Ford

The same goes for Ford vehicles (source: More Power Tuning):

• Coming from a complete stop, set the vehicle’s parking brake.
• Put the gear shifter in ‘Park’ before turning off all accessories.
• Reach normal operating temperature by letting the engine run.
• After which, allow the mill to idle for at least one minute.
• Turn the A/C on, and allow the engine to idle for another minute. 
• Next, release the parking brake.
• While pressing the brake pedal and the A/C still on, put the car in ‘Drive’ and idle the engine for another minute.
• Drive the vehicle for approximately 100–200 miles to complete the Relearn Procedure. Just make sure not to go ham when driving for the first 30 miles. Otherwise, the ECU/ECM may have difficulty relearning and adapting to your driving style.

In some cases, disconnecting the battery when resetting the ECU may no longer be necessary. Some cars have a “Clear KAM” (Keep Alive Memory) command in the “Special Functions” menu of their SCT device. This command enables vehicle owners to clear KAM codes without disconnecting the battery.

How to Reset the ECU/ECM Without Disconnecting the Battery:

• Pop the hood and locate the fuse box.
• Remove the fuse cover, then the ECU/ECM fuse.
• Leave the fuses for at least 10 seconds or up to 15 minutes.
• Reinstall the car computer fuse and replace the fuse cover.
• Take out your vehicle for a test drive.

When resetting car computers with a diagnostic scan tool, it is sadly not what OBD-II/DRB-III scanners are designed for. Because the interface of these scan tools “can implement several different data buses with different voltage levels,” it could potentially damage something in the ECU/ECM if the latter is electrically damaged and the bus lines connect to +12V.

Furthermore, these scanners cannot (and MUST NOT) operate if the vehicle is not running. The most that diagnostic scan tools can do is clear specific error codes. However, an ECU/ECM reset will have to be done differently.

How to Reset a Jeep Grand Cherokee Computer 

Resetting the ECU or ECM of your Jeep Grand Cherokee entails six steps, which are pretty similar to the lists above. The only exception is that you do not need to take out your OBD-II/DRB-III scan tool and can go straight to performing the steps below:

1. Prep Your Cherokee

First, you will need to prep your Cherokee for ECU reset by letting it sit for an hour prior. It is important to start an ECU reset with a cold engine. Otherwise, you risk incurring burns. Once the engine is cold enough, insert your key into the ignition without turning it to the “ON” position. Pop the hood and find the battery (usually found in the front of the engine compartment or to the left of the engine).

2. Disconnect the Battery

Next, you will need to disconnect the battery. Do this by removing the positive battery cable (red color) from the positive battery terminal. It should be easy to identify the positive cable as it comes with a plus sign (+). Conversely, the negative battery cable has a minus sign (-). If you do not show these indicators or are unsure where to look, refer to the wiring diagram in your owner’s manual.

3. Ground the Cables

Ground the positive and negative cables by connecting them and leaving them like that for at least half a minute. As established earlier, this step releases any remaining electric charge in the airbag system and capacitors.

4. Let the Vehicle Rest

Once power has completely drained from the capacitors, let the vehicle rest. You may or may not observe the 45-minute waiting period at this point. After which, remove the grounding of the positive and negative battery cables and reconnect these to the battery.

For guidance on appropriate steps, though, refer to Cherokee-dedicated forums or your owner’s manual. Do not forget to close the hood once the battery is back in its compartment.

5. Test the Lighting System

Test your lighting system by switching the headlights on and off. However, you will need to do this test with your ignition key turned to the “ON” position but without starting the engine. Furthermore, there should be a 10-to-20-second interval between turning the headlamps on and then off afterward.

6. Drive

You have successfully reset your Jeep Grand Cherokee computer, wiped out its stored memory, and restored it to factory settings. The next stage is to allow your vehicle to relearn your engine and driving habits, which you will accomplish over the next hundred miles or so of driving.

When Should You Reset Your ECU?

Here are common symptoms and situations that indicate a failing ECU and call for a car computer reset:

• Intermittent and long-standing Check Engine Light
• Unstable or erratic engine behavior
• Sensor/engine issues
• Burning smell
• Noticeable problems with electronics such as a frozen touchscreen, non-working audio, or inoperable switches and climate controls
• Wanting to restore your vehicle to factory settings

Some telltale signs may be caused by other triggers like severe wear and tear or physical damage to specific vehicle components. If so, you may need to do more than an ECU reset. When in doubt, seek assistance from a professional mechanic to get your car computer or problematic car parts properly diagnosed and configured.

Conclusion – How to Reset a Car Computer

In summary, here are nine simple steps on how to reset car computers:

1. Use a high-spec diagnostic scan tool.
2. Turn off your car battery.
3. Insulate the battery wires.
4. Do a soft reset.
5. Remove the ECU/ECM fuse from the fuse box.
6. Observe the 45-Minute Waiting Period.
7. Put the battery back in place.
8. Reset radio and clock presets.
9. Complete the Idle Relearn Procedure.

Following the steps in this guide will prove beneficial, even if you are not a car mechanic. They should help you save up on unwanted tech fees since you can now do simple ECU resets by yourself and need not visit your local repair shop each time. Ultimately, some steps may differ depending on your car’s make and model. That said, have your manual handy when doing this procedure.

Resetting the ECU usually follows an unsuccessful attempt at clearing the Check Engine Light and should never be used as a shortcut to pass emissions testing. The latter is one of the biggest myths regarding computer resets.

While an ECU reset can get rid of a flashing CEL, the emissions team will still be able to pick up on existing issues with your vehicle or its onboard computer as they conduct electronic diagnostics beyond your car’s OBD-II port (among other tests). And lastly, you need to have driven at least 100 miles from when the last DTC was cleared for you to get a “pass” from the emissions technicians.