Jeep Wrangler P0138 – Engine Code Solution – O2 Sensor Circuit High Voltage

What does the Jeep code P0138 mean?

The P0138 engine code stands for “O2 Sensor Circuit High Voltage” which means there’s a problem with the oxygen and fuel output of your catalytic converter. While not dangerous for your engine, driving like this could damage the catalytic converter over time.

Jeep Code P0138

  • O2 Sensor Circuit High Voltage

Symptoms of code P0138

  • Engine light is on
  • Rough idle
  • Strong fumes coming from your car
  • Poor fuel economy

Causes of code P0138

  • Faulty O2 sensor
  • Shorted battery in O2 sensor
  • High fuel pressure

Fixes for code P0138

  • Replace the O2 sensor or repair its battery
  • Replace the fuel pressure regulator

Cars are incredible. They do all sorts of amazing things – sometimes, things that we don’t even notice. How the O2 sensor monitors oxygen output is one of those things.

These sensors generate electricity for the car’s computer to know whether the oxygen and fuel output are balanced or not.

When the O2 sensor generates high voltage, there’s too much fuel in the mix; when the O2 sensor generates low voltage, there’s too much oxygen in there.

So, you can probably guess the P0138 code is caused by having too much fuel (or little oxygen) in your catalytic converter output.

Because, yes, the O2 sensors work with the catalytic converter to make sure your car isn’t polluting the environment.

When the P0138 happens, you either have an issue with your catalytic converter or your O2 sensor.

Can I drive with a P0138 engine code?

You can drive around for a couple of days after you get a code P0138 – but you shouldn’t delay repairs any more than necessary. While a broken sensor is nothing to be afraid of, you don’t want to mess with your catalytic converter.

The code P0138 can go one of two ways: you have a broken O2 sensor or something is up with your fuel pressure.

The first one is not that bad (but still a problem), while the second one can get you in trouble down the road.

Because of that, it’s better to diagnose and start working to repair or replace whatever stopped working properly.

Although you shouldn’t worry too much about faulty sensors, there are times when even they can cause a lot of trouble, though. I’ll talk a little bit more about it down below.

Can a bad O2 sensor cause a misfire?

On rare occasions, a malfunctioning sensor can give a bad enough reading for your engine to start misfiring and cause a lot of trouble in the process. If you suspect your O2 sensor is causing an engine misfire, you need to fix that issue right away.

A faulty sensor will always give a bad reading. That can cause your car to go crazy.

Most of the time, it’s nothing but a manageable problem – but, sometimes, you can experience a worst-case scenario.

Your O2 sensor affects your engine combustion and timing, among other things. That means that it can make your engine misfire and overheat (if you’re unlucky enough).

Let me remind you that’s on rare occasions!

You shouldn’t start to panic when you see the code P0138 and think your engine is about to break – but you should keep an eye on things, just in case.

How much does it cost to replace an O2 sensor?

An O2 sensor can cost anywhere from $25 to $100 on its own. If you have to take labor costs into account, the price for the entire thing shoots up from $100 to $500 depending on your car model and what you need.

I know, I know. Replacing an O2 sensor gets drastically expensive when you go to a repair shop.

It’s worth it, though! You know how important this sensor is – and what could happen if you drive around with one that doesn’t work properly.

And look, I get it. You probably researched online and most people are saying that changing an O2 sensor is easy – well, that’s not entirely true.

You need plenty of tools that you probably don’t have (like an oxygen sensor socket) for this job.

At the end of the day, you’ll end up spending more money on tools than you would at the repair shop – and you still need to replace the sensor after spending that money!

If I were you, I’d drive to the mechanic and pay for both the sensor and peace of mind.

If the O2 sensor is working properly, you have problems with your fuel pressure.

How can I test my fuel pressure?

The easiest way to test your fuel pressure is by using a fuel pressure tester. That’s the fireproof way of doing it. You can also do manual and visual tests and get a more or less accurate reading of things.

If you have a tester, you can manage to test your fuel pressure on your own. What if you don’t have one, though? You need to pay attention to the three signs of low fuel pressure.

The three signs of low fuel pressure:

  1. Shaky Engine Start
  2. Engine Power Loss
  3. Engine Sputters at High Speeds

If you recognize any of these three signs, you need to take things further and check the fuel pressure. Ideally, you’d have a fuel pressure tester – but if you’re down here, you probably don’t.

How to test fuel pressure without a tester

Hearing Test

Look for the fuel pump. Turn your car off and wait for a couple of seconds. Then, turn the car on and see (or rather, try to hear) if the pump fuel starts to buzz.

No buzz? You may have fuel pressure issues. If your O2 sensor is working fine but you hear no buzz, your fuel regulator probably caused the entire thing.

Visual Test

This one is a bit of an obvious sign, but you still need to look for it. And if you happen to spot this one, you definitely have a faulty fuel regulator.

I’m talking about black smoke!

If you find dense black smoke coming out of your exhaust, your fuel regulator is broken – and probably causing the code P0138.

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