From a P0344 to a P0340 CMP Code
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JK Newbie
Joined: Oct 2023
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From: Griffin, GA
From a P0344 to a P0340 CMP Code
Hey, new to the forum and I'm hoping someone can help shed some light on an issue I'm having.
I have a 2008 Jeep Wrangler 2 door and had been suffering from a dying battery the last week or so. Last week, I parked and could no longer get the jeep to start - showing all the usual "your battery has died" signs and I had to have a friend come and jump me. Got the jeep started and was just letting it idle to get the battery up enough to get home and about 15 min later, the jeep just shut off. I started it again and it was missing like crazy and went into limp mode. Pulled my code reader out and found a P0344 stored so, I already new what this was so I went ahead and limped the jeep back to the house. Went to autozone and ordered a new CMP which I got the next day and a new battery as my other tested bad, which is what I figured with the random electrical glitches I had been having the whole week or so.
After swapping out the CMP, the jeep started but was idling rough but, smoothed out around 1000 rpms where the ECU kept it after a few failed tries at letting the rpms come down... but after it warmed up, it had more and more trouble keeping the rpms steady, can't get over 2700 or so with out it reving back and forth (limp mode), still no peddle, etc.. basically the same issues as before but with a new CMP. Pulled codes again and found the P0344 had been replaced with P0340 circuit code. Tested the circuit and the 5v ref was at 4.83v, grnd tested good and the signal wire solid at 5.01v. Ok, so good there.... started looking at the sensor again, took it back to autozone and had them order a replacement. installed the new CMP and same issues but, the jeep was acting a lot more erratic with the same P0340 code being thrown. Decided to test the circuit again and this time, the 5v ref wire was testing at 4.2v. Everything else stayed the same.
Anyway, this is getting a bit long winded so basically, replaced coil, wires, and plugs (needed the tune up anyway) and the issue is unchanged. My concern focused on the 5v ref wire.... decided to test it again, this time it tested out at 3.77v (?) ECU?? Short?? both?? today, that same line is testing out at a solid 2.56v. I found a good schem for the wiring to the ECU/PCM, pulled C1 and removed the cover, found my wire and it's testing out at 2.34v straight out of the ECU so now I'm thinking bad ECU, right?? BATT V to the ECU on both pins in C1 is a solid 12.6v, so good supply and both grounds test good but, with C1 disconnected, checking my 5v wire for a short confirms it is shorted to ground somewhere so, I pulled the plugs on all 5 sensors the schem says are connected to that one 5v wire, the CMP, MAP, EGR, Gas Peddle, and the Line Pressure Sensor on the tranny figuring maybe another sensor on the 5v wire was causing the issue. Short is still present so, deeper in the harness... still trying to work out where it's at.
I guess my question is: Could it be the short that is causing the ECU to produce the lower voltage (i.e. find and fix the short and problem solved, ECU is good to go) or is it just a bad ECU along with a shorted 5v line?
Thanks for any help!
I have a 2008 Jeep Wrangler 2 door and had been suffering from a dying battery the last week or so. Last week, I parked and could no longer get the jeep to start - showing all the usual "your battery has died" signs and I had to have a friend come and jump me. Got the jeep started and was just letting it idle to get the battery up enough to get home and about 15 min later, the jeep just shut off. I started it again and it was missing like crazy and went into limp mode. Pulled my code reader out and found a P0344 stored so, I already new what this was so I went ahead and limped the jeep back to the house. Went to autozone and ordered a new CMP which I got the next day and a new battery as my other tested bad, which is what I figured with the random electrical glitches I had been having the whole week or so.
After swapping out the CMP, the jeep started but was idling rough but, smoothed out around 1000 rpms where the ECU kept it after a few failed tries at letting the rpms come down... but after it warmed up, it had more and more trouble keeping the rpms steady, can't get over 2700 or so with out it reving back and forth (limp mode), still no peddle, etc.. basically the same issues as before but with a new CMP. Pulled codes again and found the P0344 had been replaced with P0340 circuit code. Tested the circuit and the 5v ref was at 4.83v, grnd tested good and the signal wire solid at 5.01v. Ok, so good there.... started looking at the sensor again, took it back to autozone and had them order a replacement. installed the new CMP and same issues but, the jeep was acting a lot more erratic with the same P0340 code being thrown. Decided to test the circuit again and this time, the 5v ref wire was testing at 4.2v. Everything else stayed the same.
Anyway, this is getting a bit long winded so basically, replaced coil, wires, and plugs (needed the tune up anyway) and the issue is unchanged. My concern focused on the 5v ref wire.... decided to test it again, this time it tested out at 3.77v (?) ECU?? Short?? both?? today, that same line is testing out at a solid 2.56v. I found a good schem for the wiring to the ECU/PCM, pulled C1 and removed the cover, found my wire and it's testing out at 2.34v straight out of the ECU so now I'm thinking bad ECU, right?? BATT V to the ECU on both pins in C1 is a solid 12.6v, so good supply and both grounds test good but, with C1 disconnected, checking my 5v wire for a short confirms it is shorted to ground somewhere so, I pulled the plugs on all 5 sensors the schem says are connected to that one 5v wire, the CMP, MAP, EGR, Gas Peddle, and the Line Pressure Sensor on the tranny figuring maybe another sensor on the 5v wire was causing the issue. Short is still present so, deeper in the harness... still trying to work out where it's at.
I guess my question is: Could it be the short that is causing the ECU to produce the lower voltage (i.e. find and fix the short and problem solved, ECU is good to go) or is it just a bad ECU along with a shorted 5v line?
Thanks for any help!
