P1391 help

[Tinnitus_Z]

Hello, I am new to forums and I don't really know how these work too well so I may be asking wrong. Anyway, after replacing O2 sensor 1 (bank 1 and bank 2) today, I now got the code P1391 for the crankshaft position sensor or camshaft position sensor. I have a 2002 manual 4.0 TJ and I already replaced the crankshaft position sensor around 2 weeks ago with a brand new NTK one designated for manual transmission. I also replaced the camshaft position sensor with my dad around a year ago, but I am unsure of what brand as we got it from Autozone.

I also have P0455 for a large leak detected in the EVAP system, which I already know the cause of, but I temporarily fixed it yesterday. Now I am unsure what to do since both CKP and CMP are relatively new and appear to be working fine. There is a little rough idle and a bad throw out bearing but neither of those things are from the CKP or CMP, atleast I think so. Any help is appreciated.

 

[CharlesHS]

The P1391 can be either the CmPS or the CkPS and on some occasions a generic code for a 5V reference voltage problem.

How to test for a bad CkPS.

 

[Jerry Bransford]

Welcome to the forum! That was an NTK O2 sensor you installed today right? Bosch and most aftermarket/store brand O2 sensors are notorious for not working properly in a TJ.

 

[Tinnitus_Z]

Welcome to the forum! That was an NTK O2 sensor you installed today right? Bosch and most aftermarket/store brand O2 sensors are notorious for not working properly in a TJ.

Well I installed two different O2 sensors. My dad accidentally broke Bank 2 Sensor 1 a couple of days ago so he had to buy one immediately and got the only one remaining from Autozone, most likely Bosch since they only carry that at my location for some reason. I bought and installed the NTK 23139 for Bank 1 Sensor 1 from Rockauto. The Sensor 2 O2 sensors were replaced a couple of years ago, but I have not gotten any codes for Sensor 2 yet.

 

[Tinnitus_Z]

The P1391 can be either the CmPS or the CkPS and on some occasions a generic code for a 5V reference voltage problem.

How to test for a bad CkPS.

Thanks, I'll check those out

 

[Jerry Bransford]

Well I installed two different O2 sensors. My dad accidentally broke Bank 2 Sensor 1 a couple of days ago so he had to buy one immediately and got the only one remaining from Autozone, most likely Bosch since they only carry that at my location for some reason. I bought and installed the NTK 23139 for Bank 1 Sensor 1 from Rockauto. The Sensor 2 O2 sensors were replaced a couple of years ago, but I have not gotten any codes for Sensor 2 yet.

A Bosch O2 sensor will cause problems. They are set up for a different bias voltage than the TJ provides.

 

[Chris]

Yep, Bosch sensors are known to cause issues. This is very well documented on the forum.

 

[Tinnitus_Z]

A Bosch O2 sensor will cause problems. They are set up for a different bias voltage than the TJ provides.

Just found out it was a Walker O2 sensor, would a wrong O2 sensor cause the P1391 code? It started showing up after I replaced the O2 sensors.

 

[Jerry Bransford]

Just found out it was a Walker O2 sensor, would a wrong O2 sensor cause the P1391 code? It started showing up after I replaced the O2 sensors.

Unlikely since that's a timing problem with the camshaft position sensor.

 

[Cross-Threaded-06TJ]

I'm going to give you the answer. It won't be the answer you want.

The correct way to diagnose your issue is to use a dual pattern oscilloscope and monitor(backprobe) the cam and crank sensors while cranking and running. A guy can actually buy his own scope on amazon nowadays for not that much. Even a dual pattern

Or take the Jeep to a trustworthy shop and ask/pay them to do this. A good shop will have Mitchell or identifix etc programs that will tell the tech what the patterns should be and they can watch them and easily figure this out. Also they can verify the 5v and grounds are good.

The scope will tell you which sensor is causing the issue.

Or throw parts at it til it runs right.


Welcome to the forum BTW!