Any follow up on why the vehicle ran better after clearing codes (maybe learned values too) ?
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I don't know , After I changed the accelerator position sensor and cleared the codes the APP sensor 1 registered voltage change fine ,It started and ran fine and after an hour stalled and after clearing codes with scan tool started up. I referred to power supply cleaned ground E15 and bunch of grounds in the engine compartment , unplugged and re-seated throttle body connector, drove it around for entire entire day without issue other than Air conditioning would intermittently stop working at times. Customer did not want me to go into that issue. Customer drove for 3 days before it quit and had to tow it. I went back into it and could see no APP sensor1 (Accelerator Pedal Position Sensor 1)voltage change. Due to the hooded hinge and lever design of the PCM connectors and small gauge wires I had to use small diameter sewing pins in the connector terminals themselves to test continuity and load tested APP sensor 1 wires from one end to another with a bulbed test light which lit up just fine yet no 5 volt reference was available to the APP sensor1 wire that should of had it . All fuses tested good. I figured I would go back to basics and test fuel pressure and spark before condemning the ECM,No fuel pressure test port but could hear fuel pump relay clicking inside the Intelligent Power Distribution Module, but no fuel pump sound in back when activating with my scanner and back probed brown wires of connector at IPDM and found the fuel pump power feed wire was indeed powering up.Threw all the garbage into the hatch area and removed rear seat, accessed fuel pump connector and verified good power and ground , but fuel pump was dead. Told the customer the fuel pump needs to be changed and car will start , but don't think ECM 5Volt feed to APP sensor 1 suddenly is mysteriously going to fix itself and turn back on with a new fuel pump installed , unless the IPDM is selectively cutting one of the power feeds to ECM or something.
...and yes I did install a new Nissan APP sensor , not a salvage yard one. Surprised it was less than $50