Hello,
I'm new to the forum, but have been a TJ owner for over 12 years now, and have used this forum as a reference multiple times in the past.
I have an 06 TJ with the 4.0L and automatic transmission (NGC computer)
My jeep recently encountered a hard start/no start issue and died on me a few miles away from home, the verdict was a P0340 CMP code along with a P0129 Barometric Pressure Too Low code.
I purchased a new sensor from O'Reilly (Standard Ignition brand, ~$60), however I performed some electrical testing to verify that the crank position sensor and the cam position sensor were receiving appropriate power from the PCM. I verified voltage supply, ground and signal to the connectors for both sensors. After doing so and finding no issues, I installed the new sensor, only to find that my hard start issues persisted, and the jeep was behaving the same as before.
My next thought was that perhaps the PCM needed to be reset and I needed to stop working for the day so i left it disconnected over night just to be extra sure the PCM had no more capacitance (i also made sure to touch the positive and negative terminals together). The next day i reconnected the battery, the check engine light remained, in addition to the same diagnostic codes. During this time, the jeep would drive well under low RPM, but at higher RPM it would surge. After driving it around for a bit, the issue didn't resolve itself and the jeep wouldn't start after getting up to temperature.
To verify that this wasn't a wiring harness issue, I performed resistivity tests from the CMP sensor connector to the PCM connector pin. All tests were satisfactory. I then installed another sensor from amazon (identical to the standard ignition sensor, same wire colors and everything, but it was $40 cheaper). Low and behold, my jeep started like new and the CEL disappeared. I test drove it in my neighborhood and it did fine, I'm now back to daily driving it.
MY REASON FOR THIS POST:
I saw several posts stating that with the replacement of a cam position sensor you have to perform a relearn procedure with an appropriate scanner to reestablish the relationship between the crank and cam sensors. THIS WAS NOT NECESSARY. I had the unfortunate luck of purchasing a bad sensor at first from O'Reilly, however, with purchasing a good new sensor, I DIDN'T HAVE TO DO ANYTHING other than install the sensor, no computer, no relearn. The CEL cleared itself and my jeep is driving fine. I was on the verge of buying a capable scanner (~$200) but I'm happy i didn't. If i did need to replace the OPDA then i believe this would be necessary, however, for the common sensor replacement it is not necessary.
I wanted to write this up so that anybody else encountering this issue could have a good reference point. Also so people can be aware that when buying parts from the autoparts store, you're viable to get a 'dud'. This is the second time this has happened to me, the first was with the windshield wiper, turn signal steering column assembly (i think that's what its called lol).
I also wanted to take the time to thank the community on here for pooling together all the resources such as the interactive wiring diagram, the factory service manuals, and the DTC manual. Amazing resources, you are practically unstoppable at troubleshooting and fixing your jeep as far as information goes.
If a reader has questions, i will do my best to answer.
I'm new to the forum, but have been a TJ owner for over 12 years now, and have used this forum as a reference multiple times in the past.
I have an 06 TJ with the 4.0L and automatic transmission (NGC computer)
My jeep recently encountered a hard start/no start issue and died on me a few miles away from home, the verdict was a P0340 CMP code along with a P0129 Barometric Pressure Too Low code.
I purchased a new sensor from O'Reilly (Standard Ignition brand, ~$60), however I performed some electrical testing to verify that the crank position sensor and the cam position sensor were receiving appropriate power from the PCM. I verified voltage supply, ground and signal to the connectors for both sensors. After doing so and finding no issues, I installed the new sensor, only to find that my hard start issues persisted, and the jeep was behaving the same as before.
My next thought was that perhaps the PCM needed to be reset and I needed to stop working for the day so i left it disconnected over night just to be extra sure the PCM had no more capacitance (i also made sure to touch the positive and negative terminals together). The next day i reconnected the battery, the check engine light remained, in addition to the same diagnostic codes. During this time, the jeep would drive well under low RPM, but at higher RPM it would surge. After driving it around for a bit, the issue didn't resolve itself and the jeep wouldn't start after getting up to temperature.
To verify that this wasn't a wiring harness issue, I performed resistivity tests from the CMP sensor connector to the PCM connector pin. All tests were satisfactory. I then installed another sensor from amazon (identical to the standard ignition sensor, same wire colors and everything, but it was $40 cheaper). Low and behold, my jeep started like new and the CEL disappeared. I test drove it in my neighborhood and it did fine, I'm now back to daily driving it.
MY REASON FOR THIS POST:
I saw several posts stating that with the replacement of a cam position sensor you have to perform a relearn procedure with an appropriate scanner to reestablish the relationship between the crank and cam sensors. THIS WAS NOT NECESSARY. I had the unfortunate luck of purchasing a bad sensor at first from O'Reilly, however, with purchasing a good new sensor, I DIDN'T HAVE TO DO ANYTHING other than install the sensor, no computer, no relearn. The CEL cleared itself and my jeep is driving fine. I was on the verge of buying a capable scanner (~$200) but I'm happy i didn't. If i did need to replace the OPDA then i believe this would be necessary, however, for the common sensor replacement it is not necessary.
I wanted to write this up so that anybody else encountering this issue could have a good reference point. Also so people can be aware that when buying parts from the autoparts store, you're viable to get a 'dud'. This is the second time this has happened to me, the first was with the windshield wiper, turn signal steering column assembly (i think that's what its called lol).
I also wanted to take the time to thank the community on here for pooling together all the resources such as the interactive wiring diagram, the factory service manuals, and the DTC manual. Amazing resources, you are practically unstoppable at troubleshooting and fixing your jeep as far as information goes.
If a reader has questions, i will do my best to answer.
