This article applies to the Jeep Grand Cherokee WJ (1999-2004).
The check engine light (CEL) doesn’t give you much information, but the five most common reasons why the light comes on in most vehicles include a faulty oxygen sensor, loose or faulty gas cap, faulty catalytic converter, faulty mass airflow sensor, or failing spark plugs and/or wires. Running a diagnostic will give you more information about why the light is on. This diagnostic tool, known as a code reader or scan tool, can also turn off the light, but unless you address and resolve the underlying issue, the light will come on again after you’ve driven between 25 and 50 miles. Using the tool is relatively simple and if you don’t have one, you can get one at most auto parts stores.
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Method 1 – Using an OBD scanner
Step 1 – Find the data link connector
The data link connector (DLC) allows you to connect the OBD scanner to your Jeep’s ECU.
- Make sure your Jeep is off before starting.
- Open driver’s side door and reach under the dashboard. The DLC is located on the far left side, toward the front and slightly diagonal to the steering wheel.
Step 2 – Connect the diagnostic scanner
- Plug the scanner into DLC and then turn on your Jeep Cherokee.
Step 3 – Run the diagnostic scan
- Turn on the scanner and go to the appropriate screen for diagnosing why your Cherokee’s CEL is on. The diagnosis may take a few minutes to fully run.
- When the diagnosis is complete, your scanner will generate a list of codes specific to what’s causing the light to come on. If you’re not familiar with the codes and what they mean, your owner’s manual may include this information. Write down the list of codes that your scanner generated after completing the diagnostic scan.
Step 4 – Reset the check engine light
- Leave the scanner connected to the DLC. The scanner will ask if you want to erase all diagnostic results and codes. Select “YES.”
- Put your key in the ignition and turn it to the “ON” position. Do not start the engine.
- Press enter on the scanner once you’ve done this. The scanner will communicate with your Cherokee and tell it to turn off the CEL.
- Start the engine. The CEL should now be off.
Method 2 – Without using an OBD scanner
Step 1 – Reset your check engine light
- Disconnect the positive (red) battery cable.
- Ground the positive battery cable to negative (black) battery cable for around 30 seconds.
- Reconnect the positive battery cable.
- Turn your key into the “ON” position, but do not turn on the engine.
- Turn headlights on, and leave them on for 10 to 20 seconds.
- Then turn the headlights off.
- Turn your key into the “OFF” position, and let the car sit for about one minute.
- Turn your key into the “ON” position, and then start your engine. The CEL should now be off.
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