I have a 2008 Dodge Grand Caravan with the 3.8 liter engine that has a stubborn P0172 code. I had changed the O2 sensors (both) a few months ago (NGK ? four-wire, not five wire), as well as the injectors. I also cleaned the MAP and MAF sensors and the throttle body, replaced the PCV valve, EGR valve, and coil (#1 cylinder had no spark -dead coil). After I did all that, I cleared the counters and relearned the throttle position (I use AlfaOBD). The odd thing is that it actually runs pretty good. Only a slight roughness to it ? which I attributed to it having 260,000 miles on it. I also did run a can of CataClean through it. So I disconnected the upstream O2 sensor and probing the heater wires returns 4 ohms ? within spec so the heater wire is likely intact and the sensor is probably good. I pulled the fuel rail and pressurized it and no injectors were leaking. Reassembled it ? still had P0172. Sprayed some starting fluid around the injectors and it made no difference. Once the engine reaches temp, the short term adaptive bank 1 jumps to -25% and stays there. I checked the purge solenoid and it checks out good. The MAP sensor reads 1.2v at idle ? well within spec. I also checked the exhaust manifold to rule out sucking in air ahead of the O2 sensor. No leaks. The 1/1 O2 sensor fluctuates around 3.3v +- .2v when idling. With the key on/engine off and the O2 sensor unplugged, when I probe the harness side, I?m getting 4.2v where I expected to see 12v (the heater power line) and a constant 2.5v where I expected to see the 5v reference (signal line). So I unplugged the pedal sensor, MAP sensor, and MAF sensor and still have 4.2v. I also unplugged the C1 and C2 connectors on the PCM and still had 4.2v so that probably rules out a failing PCM. If failing, the voltage should have gone to zero. I have the NGC4 PCM and so tested resistance on C2 pin 3 to C1 pin1, C2 pin 32 to C1 pin 1, and C2 pin 3 to C1 pin 11, C2 pin 3 to C2 pin 32, and C2 pin 3 to C2 pin 33 and all were open, which further validates that the PCM is probably not the issue. I even pulled the M19 O2 heater fuse and still had 4.2v on the O2 heater line. I do still have to unplug the cam and crank sensors just to verify that they aren?t bleeding voltage to the O2 heater line but it was getting too dark to continue. I?m about at my wits end and running out of things to check. Any ideas would be greatly appreciated.