Determine which transmission is installed on your Jeep.
Jeep check engine light (CEL) comes on when the On-Board Diagnostic (OBD) system detects a problem with the engine, transmission, or evaporative system.
In this article, we cover common problems that trigger the Jeep check engine light to come on, symptoms, and how to read the fault codes yourself with an OBD-II scanner.
Common symptoms that you notice when Jeep check engine light comes on:
- Check engine light always on
- Engine runs rough
- Engine misfire present
- Lack of engine power
- Poor throttle response
- Engine noise
- Smoke from exhaust
How to Diagnose Jeep Check Engine Light
The first step in the troubleshooting process is to read the fault codes from the Engine Control Unit. This is a simple procedure that you can perform yourself with an OBD-II scanner.
- Locate the OBD-II port under the dashboard and plug in your scanner.
- Turn on the ignition but do not start the vehicle.
- Turn on the scanner and allow it to communicate with the vehicle.
- Select Read Codes or Read Fault Codes depending on the scanner.
Write down the codes that show on the screen of your OBD-II scanner. For example, a fault code may show as P0301 or P0300. Research those codes to get a better understanding of the problem.
Most common causes that trigger check engine light include:
- MAF Sensor
- Oxygen Sensor
- Spark Plugs
- Ignition Coils
- Catalytic Converter
- Loose Gas Cap
In the next section, we go over some of the most problems that trigger the Jeep check engine light.
Thermostat: Engine thermostats that are stuck or not opening all the way are a fairly common problem on Jeep vehicles. Other than a check engine light, you might also experience engine overheating or high fuel consumption, depending on the failure mode. In both cases, the thermostat should be replaced without a delay. Code: P0128 - thermostat not performing properly
EGR Valve: On Jeep engines, EGR related problem is usually caused by a stuck EGR valve. If stuck open, this can even cause rough running, misfire, and stalling. In most cases, a carbon buildup within the valve prevents proper operation. If not too severe, this can be cleaned with EGR cleaner spray. Code: P0404 - EGR performance
Catalytic Convert: Higher-mileage Jeeps are likely to have issues with emission control systems. In most cases, this is caused either by a worn catalytic converter or dirty O2 sensors. Pinpoint the root of the problem before replacing expensive parts. Codes: P0420 and P0430 - Catalyst Efficiency Below Threshold
EVAP Leak: A check engine light accompanied by a strong gas odor could indicate a leak within the EVAP system. Purge solenoid is a first thing to check for leaks, along with fuel ventilation lines. Some models have a Leak Detection Pump, which can go bad. Codes: P0456 - small evap leaks, P1494 - Leak Detection Pump faulty or evap leak.
Transmission: Gearbox related problems can trigger the check engine light, as well. You may be experiencing issues such as harsh shifting or being stuck in 2nd gear, which is called a limp mode. In most cases, replacing the transmission valve body fixes the problem. Fault Code: P0740
Throttle Body: Newer Jeeps with 4-cylinder engines are quite prone to electronic throttle body problems. This will cause rough idle, loss of power, and poor throttle response. In some cases, it can even trigger extremely limiting limp home mode. Replacing the throttle body is the only way to solve the issue. Codes: P2112 and P2112 - Throttle Actuator Control System - Stuck Open
Jeep Check Engine Light Flashing
Be extra careful if Jeep check engine light is flashing, especially if accompanied by engine shaking and juddering.
This is a telltale sign of an engine misfire, which can cause damage to the catalytic converter and other engine components.
It is not recommended to drive a Jeep if the check engine light flashing.
Jeep check engine light on but no codes
If you are reading the codes on your Jeep but are not getting any stored codes, you may be using a scanner that does not work on your vehicle. Another possible issue is that the OBD-II port is damaged.
What could cause Jeep check engine light to come on?
Problems such as loose gas cap, bad mass airflow sensor, oxygen sensors, and many other problems can cause the check engine light to come on. Without reading the codes and doing further troubleshooting it is hard to know.
Which Jeeps have a check engine light?
The check engine light is present in all 1996 and newer Jeep vehicles including Jeep Cherokee, Patriot, Liberty, Wrangler, etc.