These notes are to help me track a P0107 CEL code that I got on my 97 Jeep Wrangler.
Also see: 97 Wrangler P0740 (potentially related to root cause oof “bad” PCM)
I purchased the Jeep in September, have worked through several other CEL codes and steadily increased the performance of the Jeep. The Jeep has also been on numerous wheeling trips since I purchased it. On 24 November 2024, I took the Jeep on a trip to Storm Mountain and Bear Gulch. At the beginning of the trip (just after leaving the house), I got a P0740 code, which I had on the vehicle previously. I’ll probably start another post on my notes for that code. It’s relevant here for context and timing, but I’m not claiming that it is directly related to the P0107 code. The relevance is that I checked the code at the beginning of the wheeling trip with a scanner, and did not clear the code until the end of the trip. At the end of the trip, I scanned the vehicle again and saw the additional code, P0107. So, unfortunately I do not know the precise moment that the P0107 code was reported since the CEL light was already illuminated from the P0740.
At first, I researched potential common causes for both codes, leading to closer inspection of the Powertrain Control Module (PCM). I removed the PCM and inspected it for damage, including the wiring harnesses and attached wires. The PCM itself appeared to be in good physical condition (no visible damage of any sort). Of the three wiring harnesses attached to the PCM, the harness to the left has broken clips that are intended to hold it securely to the PCM.
However, the harness still appeared to be firmly attached. The wires are wrapped in protective tape and tubing, which I did not remove. From looking at other original wires on the vehicle, I am aware that the the wire shielding in general is beginning to decompose. I will inspect this closer depending on if/how there are additional issues in the future. I wanted to disassemble the PCM for closer inspection of the circuit board, but stopped short when I couldn’t slide the metal casing off (after removing the screws). Without knowing how the harness adapter is connected to the PCM board(s), I didn’t want to risk damage to the PCM by forcing anything before understanding the PCM assembly better.
PCM replacement boards (remanufactured and/or emulated to some extent), range from approximately $300 to $600, but I am not certain yet if there is an issue with the PCM.
After some additional research, I learned about Technical Service Bulletin (TSB) 18-08-00. I’m trying to find a more official source for these TSBs, but copies of them are scattered around the Internet (e.g., https://www.jeepforum.com/posts/1402337/). The TSB reads “Erroneous MIL illumination with DTC P0107 – MAP SENSOR VOLTAGE TOO LOW. This may occur during downhill decelerations at altitude or when performing off-road maneuvers when the engine is operating over 1500 rpm. The MIL illuminates due to the monitor running during incorrect parameters.“. While I can’t be certain yet that my DTC P0107 is related to the condition reported in TSB 18-08-00, there are some clues that it might be related.
From my research, I read other posts where people got this code after being at higher altitudes, and we got the code after doing the Storm Mountain and Bear Gulch ride (“at altitude or when performing off-road maneuvers“). Also, we certainly slowed ourselves down while going downhill on numerous occasions – using combinations of low gearing and brakes. Using low gears would put the engine RPMs over 1500 easily at times.
The technical service bulletin (TSB) 18-08-00 implies that the Powertrain Control Module (PCM) could/should be flashed with an update to resolve this issue. I’m not too concerned about this code, but wanted to make some notes about it. I cleared the code. If/when it comes back, we’ll see if the conditions are consistent again with the TSB. If the code is persistent and consistent with the TSB, I’ll try to find a Jeep dealership that might be able to help me update the PCM.
My message to a local Jeep dealership:
I have a P0107 CEL code on my 1997 Jeep Wrangler that I think is related to an old technical service bulletin (TSB), 18-08-00. The “fix” for this involves updating the software on the PCM. Do you still service old/1997 Jeeps and and [have the] the equipment to update its PCM?
Sent similar messages to a couple local 4×4 shops. I’ll wait and see if anyone responds. It’s worth a shot I figure.
Part of my “concern” is just ensuring the PCM has whatever the latest updates were that were provided by Jeep. I’m assuming this works like other electronics with flashable memory, but I suppose I could be way off base. Getting the PCM updated will at least eliminate that as the cause (I think).
All three places got back to me. The 4×4 specialty shops don’t have the right equipment. The Jeep dealership does, but its old, not serviced anymore, and they don’t know if it will work. It sounds like they are willing to give it a shot though. I might schedule an appointment.
I talked with the dealership. If they are able to successfully flash the PCM (which they are willing to try), it would cost me about $214. I’m not scheduling the service at this time because a new PCM will cost between $300 and $600 from my initial research. I might be better off just putting the $214 towards a new PCM. I also have only seen this code once, so I’m not in a big hurry to get this done. Just keeping notes for now.
I’m leaning toward the PCMs at wranglerfix.com, but I reached out to ask if/how the TSB I’m concerned with effects their PCMs.
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