Check Engine Codes P0031, P0051, P0138, P1494, & P0136

[Colben_22]

I bought my Jeep a few months ago and shortly after I got home with it some check engine lights came on. I haven't had much time to work on it yet, but I am trying to diagnose the main problem first.

The codes it is throwing are P0031 (Oxygen (A/F) Sensor Heater Control Circuit Low Bank 1 Sensor 1), P0051 (Oxygen (A/F) Sensor Heater Control Circuit Low Bank 2 Sensor 1), P0138(O2 Oxygen Sensor Circuit High B1S2), P1494 (EVAP Leak Detection Pump Pressure Switch Condition), and P0136(Sensor Circuit Low Voltage B1S2).

I also have had a cylinder 3 misfire code pop up and the engine had been running hotter than it should be.

Does anyone have a suggestion on what to check first?

 

[Chris]

I bought my Jeep a few months ago and shortly after I got home with it some check engine lights came on. I haven't had much time to work on it yet, but I am trying to diagnose the main problem first.

The codes it is throwing are 0031 (Oxygen (A/F) Sensor Heater Control Circuit Low Bank 1 Sensor 1), 0051 (Oxygen (A/F) Sensor Heater Control Circuit Low Bank 2 Sensor 1), 0138(O2 Oxygen Sensor Circuit High B1S2),1494 (EVAP Leak Detection Pump Pressure Switch Condition), and 0136(Sensor Circuit Low Voltage B1S2).

I also have had a cylinder 3 misfire code pop up and the engine had been running hotter than it should be.

Does anyone have a suggestion on what to check first?

Your codes and symptoms are indicative of bad O2 sensors. Consider that O2 sensors area preventative maintenance part and should all typically be replaced around 80k or so. If you don't know when the last time the O2 sensors were changed, I strongly suggest you change all of them, especially since those codes you're getting are suggesting that all of them are bad.

O2 sensors for these things are cheap, easy to change, and will last you around 80k miles.

I suggest checking out this thread as it's very informative and helpful. It also shows you where each O2 sensor is located:
The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

The O2 sensors you'll want for your 2004 4.0 are as follows:

NGK #23137 - Bank 1, Sensor 1 (Upstream)
NGK #23135 - Bank 2, Sensor 1 (Upstream)
NGK #23132 - Bank 1, Sensor 2 (Downstream)
NGK #23531 - Bank 2, Sensor 2 (Downstream)

Make 100% certain you buy those NGK sensors. If you use ANY other brand other than NGK, your check engine lights typically will not go away. It's very well known in the TJ community that for whatever reason or another, they reject any O2 sensor that isn't NGK.

 

[Colben_22]

Your codes and symptoms are indicative of bad O2 sensors. Consider that O2 sensors area preventative maintenance part and should all typically be replaced around 80k or so. If you don't know when the last time the O2 sensors were changed, I strongly suggest you change all of them, especially since those codes you're getting are suggesting that all of them are bad.

O2 sensors for these things are cheap, easy to change, and will last you around 80k miles.

I suggest checking out this thread as it's very informative and helpful. It also shows you where each O2 sensor is located:
The Official Jeep Wrangler TJ Oxygen (O2) Sensor Thread

The O2 sensors you'll want for your 2004 4.0 are as follows:

NGK #23137 - Bank 1, Sensor 1 (Upstream)
NGK #23135 - Bank 2, Sensor 1 (Upstream)
NGK #23132 - Bank 1, Sensor 2 (Downstream)
NGK #23531 - Bank 2, Sensor 2 (Downstream)

Make 100% certain you buy those NGK sensors. If you use ANY other brand other than NGK, your check engine lights typically will not go away. It's very well known in the TJ community that for whatever reason or another, they reject any O2 sensor that isn't NGK.

That was going to be the first thing I did replace. I just wasn't sure if that misfire could be causing the o2 sensor codes. Thanks for the help

 

[Chris]

That was going to be the first thing I did replace. I just wasn't sure if that misfire could be causing the o2 sensor codes. Thanks for the help

I suspect that misfire is a result of bad O2 sensors.