Need help with new to me 2002 TJ 4.0

[jdunbar497]

Hello,
First time owner of a Jeep Wrangler TJ. It has a 4.0L. Im in Indiana and we have had some really cold weather got into the negative temps a few weeks ago and this is when my problem started. Any thing below 40 degrees out I get a Camshaft position sensor code and p1391 code. I can clear the codes and when the jeep is at operating temp it wont have any codes. Even about 40 degrees out. I have changes sensors and Im still getting the same codes. It was above 50 degrees out on February the 3rd 2025. It had no problems starting or codes. It got down into the 26s and it threw codes this morning of February the 4th 2025. They cleared the codes and test drove it on and off and no codes came up after them being cleared.

What can I look at with with is goin on? This has the shop and myself stumped.

 

[Chris]

Hello,
First time owner of a Jeep Wrangler TJ. It has a 4.0L. Im in Indiana and we have had some really cold weather got into the negative temps a few weeks ago and this is when my problem started. Any thing below 40 degrees out I get a Camshaft position sensor code and p1391 code. I can clear the codes and when the jeep is at operating temp it wont have any codes. Even about 40 degrees out. I have changes sensors and Im still getting the same codes. It was above 50 degrees out on February the 3rd 2025. It had no problems starting or codes. It got down into the 26s and it threw codes this morning of February the 4th 2025. They cleared the codes and test drove it on and off and no codes came up after them being cleared.

What can I look at with with is goin on? This has the shop and myself stumped.

Inspect the wiring and connectors for the camshaft position sensor. Look for signs of corrosion, fraying, or any loose connections that could be affected by temperature fluctuations.

Ensure that your grounding points are clean and secure. Poor grounding can cause various electrical issues, particularly in cold weather.

Since codes P1390 and P1391 can also be related to the crankshaft position sensor, consider checking it as well. It's often wise to replace it if it hasn't been changed recently.

The issue may stem from incorrect readings from the engine temperature sensor (ECT). If it's giving inaccurate readings in cold temperatures, it could lead to problems.

With the vehicle running, use a multimeter to check for voltage at the sensor connector. Make sure you’re getting the correct voltage, which could help diagnose any electrical issues.

If the problem persists, there might be an issue with the Powertrain Control Module (PCM) itself. If it has a glitch, it may need reprogramming or replacement. I'd talk to the forum PCM expert about this, @Wranglerfix.

Sometimes, cold start conditions can make existing problems more severe. Assessing the fuel system and ignition components (like spark plugs, coil packs, etc.) to ensure they're functioning correctly during those frigid starts could be useful.

Cold weather can lead to condensation in connectors or components. Making sure everything is dry and sealed can also help.

Since the shop is stumped, it might help to get a second opinion from another mechanic, especially one who has experience with Jeep TJs. Sometimes a fresh pair of eyes can spot something that’s been overlooked.

Good luck, and I hope you get to enjoy your Jeep worry-free! If any new developments come up, keep us posted!

 

[Wranglerfix]

@jdunbar497 What is the camshaft position code?

 

[jdunbar497]

@jdunbar497 What is the camshaft position code?

I think it was p0340. I had a picture of it on my phone but my kids got to it and must have deleted it. I remember also something about bank one or A in the code reading. Im goin to have to stop at the shop and pull the code again to be sure.

 

[Wranglerfix]

The P0340 code is usually the Pcm and P0344 is usually the sensor.

 

[jdunbar497]

It is P0340 for stored code and pending code it the P1391. I can't figure out how to post pictures.

 

[Chris]

It is P0340 for stored code and pending code it the P1391. I can't figure out how to post pictures.

Bottom left of the reply box where it says, "Attach files".

 

[jdunbar497]

It is P0340 for stored code and pending code it the P1391. I can't figure out how to post pictures.

Figured the pictures.

 

[DuckNut]

Two maybe three weeks ago there was an identical thread. Search it up and it might give you additional insight.

 

[Wranglerfix]

Sorry for the late reply. Both of those DTC‘s lead back to a faulty computer. You can call me to discuss in further detail if you’d like.

Thanks,

Mark

 

[Cooper Smith]

Figured the pictures.

View attachment 591103

View attachment 591104

We had an intermittent fault with a crank sensor on a Polaris Ranger where I work. One of the CANBUS wires were shorting to ground whenever it was wet, especially in the cold. It won't hurt to ring the wires out from the sensors to the PCM. We spent next to $5000 at a shop that threw the parts cannon at it (even had the motor apart at one point dealing with Polaris tech support). Eventually I said fuck it, and took the wiring harness apart. Low and behold, when I moved the harness a certain way, a few relays would kick out. A CANBUS wire had frayed and was shorting to ground whenever water got into the mesh tape binding the harness tightly, which allowed the wires to break under tension over time. A DMM/ohmmeter may be the ticket if there's a intermittent short/open somewhere. Freeze spray may help too, if you suspect this is a temperature depending int. fault.

 

[jdunbar497]

Sorry for the late reply. Both of those DTC‘s lead back to a faulty computer. You can call me to discuss in further detail if you’d like.

Thanks,

Mark

That's what I was thinking what would be said. Not what I wanted but had a feeling it's what would be said.

 

[jdunbar497]

What all sensors are in line with the cam and crank? Are the injectors in wire with them?

 

[tnjeepguy]

https://wranglertjforum.com/threads/p0340-p0344.82880/

 

[jdunbar497]

https://wranglertjforum.com/threads/p0340-p0344.82880/

I have read this post and I have replaced both the cam and crank sensors and with the ones from napa. The shop is rechecking wires for me. I looked at it today and found an injector wire that is opened to the elements and was wounding if they were in lime with the crank and cam sensors. I think I also had read somewhere the oil pressure sensor might be in line with the 2 also. Not sure on it tho.

 

[jdunbar497]

So I got a wrangler fix computer on Wednesday in the mail. Plugged it in today 27th and I'm still getting the codes thrown. Talked to a tech at wrangler fix and he said it may have to to a relearn on the cam and crank sensors. Where can I find a wiring digram for the sensors so I can see what colors they are and start looking at my wiring. 2002 4.0 Auto wrangler x

 

[jdunbar497]

Would the map sensor or throttle sensor mess with the cam and crank sensors since they share the same 5v power wire?

 

[Mac57]

So I got a wrangler fix computer on Wednesday in the mail. Plugged it in today 27th and I'm still getting the codes thrown. Talked to a tech at wrangler fix and he said it may have to to a relearn on the cam and crank sensors. Where can I find a wiring digram for the sensors so I can see what colors they are and start looking at my wiring. 2002 4.0 Auto wrangler x

Go to the TJ Resources section on this forum. You'll find the factory service manual for your Jeep there. It contains all the wiring diagrams.

 

[jdunbar497]

Go to the TJ Resources section on this forum. You'll find the factory service manual for your Jeep there. It contains all the wiring diagrams.

Thanks I had found that last night...... I had it before saved but lost it somewhere or it would not load anything at all

 

[tnjeepguy]

@Chris maybe too new ?