I recently acquired a 2002 C5 base M6 with 3800 miles and it has 2 issues I do not know much about. First, it started throwing P1431 code, sending fuel gage to empty and lighting up the check gages light. I reset the code and the fuel gage drops to whatever amount of fuel the tank has at the moment but doesn't move after that until I reset the code again when it reappears. Next it also has a hard time starting, requiring cranking for at least 4-5 seconds and even then it still does not start sometimes. When it finally does start, it sometimes holds the revs at about 500 rpm for 2-3 seconds and then idles like normal. Car does not stall, seems to have no issues once running and is only throwing P1431. I have driven it about 1000 miles since I got it a couple days ago and have been filling up with Shell gas. I have also used two doses of Techron. Any help is appreciated.

 

3800 miles ??…looks like the car was only driven to church on Sundays !!…I don’t know what part of the country you’re in but I would fill up with “non ethanol” fuel if you can find it and wait till the fuel tank is running on fumes or at least a 1/4 tank before adding some Techron…the DTC is your right tank so if you add it to the fuel when you are more than 1/2 tank it’s not going to make it to that right tank !!…as far as the hard starting it may be a failing cam sensor…also when the fuel tank feed line loses its prime due to a leaky injector or a few other things the car may take longer to start….usually if it sits overnight…if is it hard to start after it sits cycle the key on and off a few times on that initial startup to prime the fuel system….every time you turn the key on you should hear the pump turn on for 2 seconds then shut off…if you can buy a fuel pressure gauge that may help…the starting issue may be a little harder to diagnose correctly than the P1431. Also a TSB was issued in 2003 regarding the fuel gauge…a PCM update would be required but I would try the other thing first based on the low mileage of the car. Also a good idea to fill out your profile with model year, mods, tune etc…this is especially true with electrical issues since there are slight differences year to year with wiring !!