P0340 Code (Complete loss of power and dash codes 12, 54, and 55)

Sorry for the long post, but please feel free to jump to problem statement directly.

Background:
I have been having this weird issue on my 97 TJ 4.0L (since last 2 years I have owned it now at 130k) which is a weekend warrior. It will have this burnt obnoxious smell coming from engine bay through the vents which will happen only after being restarted after a 30-40 min break like after a short non-highway city trip of 5 miles or less (like driving back after a short lunch/dinner/errand). Never used Heat/AC and often times it will just dissipate away after 5 more minutes of driving - No CEL or anything. I have taken it to the mechanic but couldn’t replicate it and he suspects it is the coolant or engine oil (I have a RMS leak) burning off of the hot exhaust. Luckily I never had this issue with any off-roading or highway trips of 1hr or more each way- but then I may have never restarted within 30 min or let the engine cool off.

Issue:/Problem Statement:
Yesterday night the same burnt smell came up after dinner and went away in like 5 minutes and I proceeded with kids for some drive through Christmas lights - 1st gear 5mph driving with clutch/break 20 minutes . On the way back home the smell came back again but kept on increasing and ended up of with high RPMs & complete loss of power. The RPMs kept going up but no power and the vehicle won’t buzz in any gear. Luckily I was within 1/2 mile from home and after several cranking and cool off I was able to crawl it home on 4low only with lot of persuasion.

Came home and used the OBD scanner and got P0340. Then read through the forums here and got the following codes with ignition key on/off 3 times - not sure if it is relevant.
12
54
55

Just got the CPS & OPDA from Napa, will start replacing stuff. What do you guys suggest? Please advise, totally clueless here.

The video for the Dash Codes, not sure if it got attached to the original post.

imahnu17 said:

Hello @jeep2fun

On the 05-06 Jeeps I was able to find the AIP electronics CPS which has worked flawlessly for me since I swapped it in.

After some searching, it was the closest to factory specs I could find which I believe to be the reason it has worked for me. That being said it hasn’t worked for everybody.

If I’m not mistaken they have a CPS for the earlier jeeps as well, might be worth looking into.

Click to expand...

I finally found this on eBay it’s says it’s for 97 4.0. It’s the one that goes below the distributor cap. Will know after it arrives.

https://www.ebay.com/p/84097828

CharlesHS said:

The code P0340 can indicate the CKPS or CMPS, but can also be a generic code for other system problems.
The code P0054 and 0055 indicate problems with the O2 sensor heating element or circuit.

Since these are sensors and communicate with the ECU; I would first start with looking at the ECU wiring harness that is routed between the firewall and valve cover. The harness is near the threaded head stud (drivers side rear corner of valve cover) and is known to come in contact and rub thru the split wire loom and wiring insulation shorting to ground. This interrupts the communications between the ECU and sensors causing engine problems.
A close inspection of the wiring loom can either confirm this is the problem or rule this out and only takes a few minutes.

Click to expand...

I am sorry for not being clear the the 54 code is the dash code the one you get on 3 times key on-off and not a OBD Code. Heading down to garage to check for the ECU wiring harness.

On a side note - what is the 1st thing to look for if the vehicle starts fine won’t buzz in forward or reverse in any gear 2h/4h but will only move ever so hesitantly only in 4low.

Update: just to get back on the road changed the Distributor, connector and plate (surely not using the right words) from NAPA but no change. Cleared the code - so no codes now either.

@Wranglerfix Do you think this can be a PCM issue ? If we can do some troubleshooting I can go ahead and order one. Please advise.

imahnu17 said:

Hello @jeep2fun

On the 05-06 Jeeps I was able to find the AIP electronics CPS which has worked flawlessly for me since I swapped it in.

After some searching, it was the closest to factory specs I could find which I believe to be the reason it has worked for me. That being said it hasn’t worked for everybody.

If I’m not mistaken they have a CPS for the earlier jeeps as well, might be worth looking into.

Click to expand...

What is an AIP CPS? Do you have an Amazon or any online link for it? I know 97 has a weired setup like the below .

https://www.morris4x4center.com/distributor-switch-plate-56027023.html

CharlesHS said:

The code P0340 can indicate the CKPS or CMPS, but can also be a generic code for other system problems.
The code P0054 and 0055 indicate problems with the O2 sensor heating element or circuit.

Since these are sensors and communicate with the ECU; I would first start with looking at the ECU wiring harness that is routed between the firewall and valve cover. The harness is near the threaded head stud (drivers side rear corner of valve cover) and is known to come in contact and rub thru the split wire loom and wiring insulation shorting to ground. This interrupts the communications between the ECU and sensors causing engine problems.
A close inspection of the wiring loom can either confirm this is the problem or rule this out and only takes a few minutes.

Click to expand...

Still trying to inspect the ECU wiring harness. Where exactly is the below area- sorry only 2 year with TJ and learning every day—

“The harness is near the threaded head stud (drivers side rear corner of valve cover)”

Is this the place (pic attached) where ECU harness enters firewall on the Driver side?

Wranglerfix said:

The 0340 leads back to:

a wire or connector in the circuit could be grounded/shorted/broken

the camshaft position sensor may have failed

the PCM may have failed

there exists an open circuit

the crankshaft position sensor may have failed

I would check every power ground and the entire harness. Double check anything you have wired in after market.

The 0340 could be a faulty pcm. I can test it for you if you would like to send it in.

Posted at 4:20.

Click to expand...

Thanks for your inputs. But do any of these codes match with the symptoms- vehicle starts fine and revs well. Doesn’t move at all in 2h/4h in any gear — but moves ever so hesitantly in 4lo with very less torque.

CharlesHS said:

This is the area I was referring to ...

View attachment 293112

Click to expand...

Thanks for the detailed pic. Mine has some space around the valve cover - I would say wiggle room. Do any of my symptoms point to a bad clutch?

CharlesHS said:

The burning smell that you reported could be a slipping clutch and the fact that the smell increased, the lack of power and high engine RPMs could certainly indicate that the clutch is totally gone....
To know for certain... you will need to remove the inspection plate in the back towards the bottom (some manual transmissions have this) or remove the starter and look inside for clutch disc dust or the odor of a burnt clutch disc.
IF you determine the clutch is in fact bad.... LUK is the preferred clutch assembly. I would recommend replacing the clutch, pressure plate, throw out bearing, flywheel and pilot bearing.

Click to expand...

CharlesHS thanks for your inputs on the clutch failure. I am also leaning towards the same conclusion now — after attributing the burnt smell and loss of power. I just think but will find out after inspecting/replacing the clutch if the P0234 or dash code 54 — was a coincidence or if it has anything to do with my issue .

Solved—
Thank you everyone for all your information and help. Finally back on the road with a brand new LUK clutch and flywheel. I must admit driving with a new clutch is a relearning process.