jeep check engine light

Why Is My Jeep Check Engine Light On? 8 Reasons Why

You’re driving along when you notice that orange, engine-shaped icon lights up on your instrument cluster.


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Once you determine it’s your Jeep check engine light, you might feel alarmed. Or maybe you already know that’s what it is.

And if your car continues to handle just fine, you might be tempted to not worry about it and just see it as a nuisance.

It’s not.

If that light has come on, that means there’s a problem. And it could be serious.

Don’t Ignore Your Jeep Check Engine Light

It might be a minor problem. But do you really want to take that gamble?

After all, if it’s something more serious, you could be left stranded. You might also end up having to spend thousands of dollars later for ignoring the repair now.

So we’ll go over eight common problems that could be causing that light to come on:

1. Loose or Defective Gas Cap

If you’re lucky, a loose or defective gas cap is the culprit. This is the cheapest and easiest fix.

But why would this cause the check engine light to come on?

It’s the gas cap that keeps fumes from leaving the fuel tank and keeps the whole system under correct pressure. So this small and inexpensive plastic part is actually a crucial part of your car’s fuel delivery system.

If you notice your check engine light turned on immediately after filling your tank, pull over and check first to see if the cap is loose. If so, simply tighten it.

If that doesn’t do the trick, then buy a replacement gas cap at an auto parts store.

Taking these two measures will save you the expense of running a diagnostic on your Jeep. But if the light remains on after these two steps, it’s time to take it in.

2. Oxygen Sensor

A failing oxygen sensor, also known as an O2 sensor, is one of the most common reasons for that Jeep check engine light to come on. And the tricky thing with the O2 sensor is that the car will continue to drive well so you might want to dismiss the light.

But an O2 sensor code will surely show up in a diagnostic test. And you’ll want to address this.

The O2 sensor measures the amount of unburnt oxygen in a car’s exhaust system. It works with the car’s on-board computer to create the fuel-to-air ratio. A malfunction in this sensor could mean as much as a 40 percent drop in fuel economy.

In other words, your car will be burning far more gas than it needs to burn. And if you continue to drive with a bad O2 sensor, you could damage your spark plugs or catalytic converter.

3. Spark Plug Wires

Unlike with the O2 sensor, you’ll usually notice a rougher idle and a drop in the engine performance when the problem is with your spark plug wires.

That’s because the spark plug wire is responsible for transferring electricity from the ignition coil to the spark plug. If the wire is faulty, then the fuel and air mixture in its respective cylinder can’t ignite. This causes the rough idling.

So even though your Jeep may still be running with a faulty wire, long-term use of it could cause serious damage to your catalytic converter.

4. Catalytic Converter

If your catalytic converter is failing, it’s going to wreak havoc on your vehicle’s exhaust system. The catalytic converter takes the carbon monoxide generated during combustion and changes it into carbon dioxide.

Replacing this part can be expensive, so it’s important to keep it in working order. This is most easily accomplished by performing regular maintenance and oil changes, as well as getting your car out onto the freeway occasionally to open it up and let it breathe!

5. Ignition Coil

When the ignition coil is the issue, you’ll know it.

Because along with your Jeep check engine light coming on, other signs of ignition coil failure include rough idle, engine misfiring, poor emissions, a reduction in power or the car simply not starting.

The ignition coil functions as an induction coil. It converts your Jeep’s 12 volts into the several thousand volts required to jump the spark plug gap and ignite the engine’s air-fuel mixture.

In other words, the ignition coil is responsible for generating the engine spark, so any problems are going to lead to performance issues.

6. Evaporative Emissions (EVAP) Purge Control Valve and/or Solenoid

They probably won’t both be defective. But just the valve or the solenoid can activate your Jeep check engine light.

The EVAP valve prevents vapors from the gas tank from being released into the atmosphere by steering them into a canister to be burned in the engine. This valve can get sticky over time and need replacement.

Like the valve, the solenoid is also key in controlling how much fuel vapor escapes into the atmosphere. It’s controlled by the engine control module or powertrain control module.

The solenoid usually needs replacing when it starts to fail and is left partially open.

7. Mass Air Flow Sensor

If you’ve been reading through this article, you’re probably recognizing a theme by now. Obviously, there has to be right air/fuel mixture to keep your engine happy.

Your mass air flow sensor, or MAF, plays into this too.

The MAF detects the volume of air as it enters your engine. It does this by heating up a thin wire or resistor.

Your Jeep’s computer then measures the electrical resistance through the MAF, while air flowing through the sensor cools its components down. The computer needs these measurements so it can direct the fuel injectors to add more or less gasoline to the air/fuel mixture.

8. Aftermarket Alarm

Just as you were starting to notice a pattern, we’re throwing a wrench into it.

If none of the above seem to be your issue, it could be that your Jeep check engine light is on as a result of an aftermarket alarm that was not installed properly.

Believe it or not, this can trigger the check engine light.

So be sure that your alarm system is up to snuff.

Give Your Jeep the Attention It Needs

If your Jeep repair is on the elaborate side, then you’ll want to head to your local Jeep dealer. Professional Jeep mechanics can best assist you because they’re the most familiar with your make and model.

But if your Jeep check engine light doesn’t require a serious repair and you have the expertise to handle the job yourself, check out our Jeep Repair Manuals. They’ll provide you with some extra guidance.

It’s almost like having a mechanic by your side!