Mhau

2007 G35x, K&N drop intakes and axleback.

Car was having starting issues, start and die or idle at 1000rpm and slowly rise on cold start. Went to the dealer and they could not figure it out. I have new throttle bodies and new MAFs, new battery. I have P0300 code and P0138 code.
Scan tool is reading 14v on start up and will rise to 17v during drive then starts to misfire and put my car into OL-fault (oxygen sensor voltage stagnant 2.275v upstream and 1.2v downstream). I put my meter on the battery and it's at 14.8 volts ??? Im confused now. Looked at IPDM, no burned fused, ecu connectors are good. I thought I may need a new alternator so I ordered one, now I'm not sure if it's that or the ECU? What regulates voltage? BTW if I drive too long my car goes into Safe-mode until voltage reaches about 15.5v at the ECU, stays running but cannot go over 5mph. At idle voltage decreases very slowly. I've looked at other posts but cannot find anything like this...ANYone??? Thank you

69GTOFarm

Sorry, no help here. Any idea what the 2 codes are? Voltage regulators are sometimes built in to the alternator. 17V seems pretty high but my Cadillac does something similar and hunting on those forums seems to indicate this is normal behavior. But, hey - that's a GM and not Nissan/Infiniti.

I know how frustrating it is to turn to a forum like this and get no response. I guess a response like this at least lets you know that you are being heard. Wish I could be of some help.

slartibartfast

iTrader: (7)

At least there are 150+ views. Sadly, OP may be unique with this issue.

Mhau

I may have found the issue. Car is going into open loop and staying there because of the ECT sensor. It doesn't throw a code but on the scan tool it doesn't seem to respond correctly. So if the car thinks it's cold and in OL it will charge at 17v.

slartibartfast

iTrader: (7)

Keep us apprised, if you will.

Mhau

ECT sensor. Car didn't throw a code but was off enough on cold starts to cause either slow or no response for temperature to the ECU.no/low temperature reading=open loop, open loop requires higher voltage for cold weather at the ECU. I knew it was the sensor because at full warm-p the temp would sit around 154 degrees and would move up very slowly during drive. Didnt even bother doing a resistance test. Sensor changed out, car doesn'
Stall during startup and doesn' misfire when started. All is well.

slartibartfast

iTrader: (7)

Excellent! Thanks for sharing your finding.