Fuel Guage Value "flipping"

jim429 · May 31, 2011

i have a 2005 chevy silverado. the low fuel level light is on no matter what. the sending unit shows 168 ohms. can't get tags due to this. they expire today. help?

jim429 · June 1, 2011

i have a 2005 chevy silverado. the low fuel level light is on no matter what. the sending unit shows 168 ohms. can't get tags due to this. they expire today. help?

i put 11.5 gl of gas in and the ohm value changed to 81 as i believe it should. check e light still on dealer says come in now what?

jim429 · June 24, 2011

went to the dealer for diagnostics. they tell me the 5 volt reference is showing 6 volts to the guage causing the check engine light to be on due to a high input on the low fuel sensor. the man in the back spent 3.5 hours on this and said to replace the pump and sending unit. i spent $400 dollars on the delphi pump replaced as told and no difference. 8 gallons of fuel put in and low fuel light still on, guage reads empty, and the check engine light is also on. still can't get tags. need help and a job.

rgv · June 24, 2011

went to the dealer for diagnostics. they tell me the 5 volt reference is showing 6 volts to the guage causing the check engine light to be on due to a high input on the low fuel sensor. the man in the back spent 3.5 hours on this and said to replace the pump and sending unit. i spent $400 dollars on the delphi pump replaced as told and no difference. 8 gallons of fuel put in and low fuel light still on, guage reads empty, and the check engine light is also on. still can't get tags. need help and a job.

that sounds a lot like a bad ground.

what does the dealer say about giving you a bill and not fixing the problem you brought it in for?

jim429 · June 24, 2011

went back today and the tech (john) is on vacation they want him to be the one to look into problem. bet they charge me again. as far as a bad ground. my limited understanding is the pcm? sends a 5 volt signal to the variable resistor ( sending unit) resistor values change with fuel level changing the voltage returning to the secondary coil in the guage. this changes the current in this coil. there are two other coils in the guage that get the same 5 volt reference signal (without going through sending unit resistor) that produce another current. the difference in these two currents causes the degree of needle deflection on guage? i don't know,but i also don't think they do either and were assuming it was in the tank. suspect if i would have been willing to pay when asked they would have changed pump&sending unit then found that it didn't fix low fuel sensor high in put they would have billed that and whatever else was their next best GUESS . maybe the pcm is bad sending a 6 volt reference instead of 5 volts ??? bought a 30 day temp tag today.help

ChevyTech77 · June 24, 2011

What does the pcm data say for a fuel level? If it's the same as what's in the tank then you need a cluster. If it's not, then you need to fix the wiring issue between the tank and the pcm. Pretty simple stuff.

jim429 · June 26, 2011

thanks chevy tech 77 ,i don't know that answer. going to dealer on monday and will ask them how and if they can pull the information out.

jim429 · June 28, 2011

no charge @ dealer on monday kept the truck 3 hrs no results still wanting to pull the tank for 300 bucks after i already put neww pump and sending unit in. went to andy's napa in west nashville the used a snap on something made guage function told me a ground problem between tank and pcm probably gave me schematic here we go spent 3 hrs looking and removing all grnds found cleaning and replaceing no luck.