Fuel tank sensor problem

S

Snetterton

CCCUK regional rep
I have just acquired a 1997 C5 from a fellow CCCUK owner. He advised me of a possible problem with fuel gauge/tank sensor.
Guess what, on the way back home although the fuel gauge read 75% and there was plenty of fuel, all of a sudden the guage went to zero and the no fuel warning came up. I stopped, waited about a minute restarted the car and the fuel gauge showed 75% again and the car ran normally for the next 20 miles home.
Anyone had this? What parts/action do I need?
Any recommendations for someone to carry out the necessary in Suffolk/Essex?
 
teamzr1

teamzr1

Supporting vendor
Your C5 has two 9 gallon gas tanks
Each has a pump and fuel sender/float

Before considering yanking them apart is most of the problem is due to the damn Ethanol in gas and older vehicles
like the C5 the fuel system was not designed to tolerate the damage from Ethanol
In most cases what happens is the Ethanol attacks the float sender card.
The float at one end slides across this card and depending on where the float rests (as the level changes) the card
outputs a resistance value that is then sent to the IPC (dash controller) and fuel gauge
The Ethanol causes the masking of the sender card to be affected and in turns produces the wrong resistance values

You could first try and use a good gas cleaner as some types clean the sender card and corrects outputting incorrect fuel levels

Tank on left side is the master and then there is a transfer tube that then goes to the right tank
As fuel is used the right tank transfers fuel back to left tank

The sender and float are attached to fuel pump, which is very long in length and a bitch to replace when doing this
with car jackstands off the ground
 
Stingray

Stingray

CCCUK Member
Back in the day the well known "C5 fuel gauge problem" was generally put down to high sulphur/sulfur in petrol. My car certainly delivered the "fuel gauge surprise" on odd occasions but it's a long time ago. I was not aware that ethanol might cause the same problem.

In either case the answer is simple - use good quality petrol.

I simply made sure I filled with Shell V-Power or Esso Synergy Supreme whenever possible and the problem went away. (I have no axe to grind against supermarket fuels but I wouldn't put them in a C5)

The added bonus for you is that these are also low ethanol fuels.
 
Stingray

Stingray

CCCUK Member
Here's a bit more information. The earlier cars, like yours and mine, were more susceptible than later cars,

"Faulty gas gauge
"The fuel sender can be affected by the high sulfur content in the fuel, and cause the gauge to read empty. They car will still operate normally, and the gas gauge will work again if you use better gas, and will usually start again when you restart the car. It's just better to use good gas. Some people have had luck with running fuel filter cleaners thru the gas tank. New fuel senders sometimes fixes this problem."

Anyway, the bottom line remains that good quality fuel should make the problem go away. Don't expect an immediate magic answer. It may take a few fills to sort it. And there's evidence that keeping the car well filled with fuel (good quality) is better than pottering around 1/4 full. It's something to do with the way the sender works and is calibrated.

By the way, does your recently acquired C5 already have a steering column lock by-pass fitted? If not - get one.
 
2vettes

2vettes

CCCUK Member
My 1999 C5 has just started doing this. I leave home with a good tank of fuel and halfway round the M25 (always just past the Clacket Lane services!) it makes me panic by suddenly coming up with a Low Fuel warning.
The first couple of times I thought perhaps it had been stuck and had been telling me there was more in when I left but then I realised that I filled it, it wasn't taking a full tank (the price of 97 would make you think it was a full tank though!).
Looks like I have the opposite situation luckily and its the Low warning that's the lie, not the level when setting off. That would be more scary.
 
teamzr1

teamzr1

Supporting vendor
You could see if your C5 or C6 have had the GM TSB PCM software update done that may help your problem
and need to use a good gas additive to keep the float electronics card clean

Operation of a typical in-tank fuel level sending unit is based on variable resistance. As
the float moves up or down according to fuel level, the resistance in the sending unit varies. This varying resistance is processed by the engine control module (ECM) and the resulting information is sent to the instrument panel cluster (IPC) for display on the fuel gauge.

In the past, the sending unit was set up so that high resistance indicated high fuel level, and low resistance indicated low fuel level.

Ethanol & Sulfur contaminants found in some of today's gasolines can form deposits on the sending unit, resulting in higher-than-intended resistance.
The high resistance from the deposits could be misinterpreted as a high fuel level, when in fact the fuel level is low.
The driver may run out of fuel, even though the fuel gauge is not indicating low or empty.

To offset this effect, engineering has begun "flipping" fuel senders, reversing the circuitry.
This means that high resistance now indicates low fuel level and low resistance indicates high fuel level.
So, if deposit build-up adds to sender resistance, the gauge will err in the direction of indicating less fuel than is actually in the tank.

The "flipping" process began in the 2004 model year, continued through model years 2005-06.
The remaining vehicles will have their fuel level sending units "flipped" for the 2007 model year.

TIP:
When diagnosing fuel sender operation, it's critical to refer to the appropriate model year information in SI, to be sure which resistance specifications apply.

TIP:
GMSPO offers GM Fuel System Treatment PLUS p/n 88861011 (88861012 in Canada) which helps protect fuel sending units from contaminating deposits.
 
teamzr1

teamzr1

Supporting vendor
The PCM has 8 software code segments for the engine and the auto tranny (as C5s the PCM controlled both)
If using the Tech-II or a tuning tool and connecting to the PCM would show you as I example here for a 2003 Z06,
what each code segments as to their part number and CVN
You compare those with as example below what GM fixes/TSBs history were for that vehicle


calid.jpg

Using that and then comparing with GM's database
As you see for the fuel segment, there was a fix for erratic fuel gauge with part # 16264703

IF yours also has that part number and CVN than your C5 has that fix,
If yours shows ta different part # than the TSB was not done and using the Tech-II or a tuning tool could install
the newest TSBs to update the PCM with the newest code segments

If you supply to me your VIN # I can show you what oldest to newest TSBs were for your C5

If you compare the fuel code segment above and what GM database shows match meaning the fuel gauge fix was done for that Z06
tisid.jpg
 
teamzr1

teamzr1

Supporting vendor
If not having access to fully functional Tech-II
I have mentioned I do custom tuning for GM vehicles for Keith of Eurovettes in the UK
He has the tuning tools I use and with this method I can replace the fuel segment with a newer one that has
the fuel gauge TSB applied and Keith flashes that into the PCM

swapsegs.jpg
 
teamzr1

teamzr1

Supporting vendor
Pete, I replied to your PM

Here again as to your VIN #, is what PCM code segments your PCM of your C5 should have to be up-to-date of all TSBs for your VIN #
Assure PCM has that TSB part number IDs update for fuel gauge
These are all the updated software TSBs related to the PCM only I see on GM database

I see there was 2 TSBs for gas gauge issue shown
If using a Tech-II I'd have all those newer code segments flashed in or with a tuning tool to be up to date


Summary​

IDSelected#Description
112593359New software to correct fuel disable feature not functioning after a battery disconnect or BCM loss of communication. Per Product Safety Campaign 04006A. Replaces all previous software.
29358681New calibration to address customer complaints of erratic fuel gauge, DTC P1431 and spark knock. Replaces all previous calibrations.
39357956Engine diagnostic calibration
416264196Transmission Calibration
516264350Transmission Diagnostic
612586127New calibration to address customer complaints of erratic fuel gauge, DTC P1431 and spark knock. Replaces all previous calibrations.
716264761System calibration
89359153Speedometer calibration
 
teamzr1

teamzr1

Supporting vendor

Chevrolet TSB 02-06-04-010A​

Make: Chevrolet Number: 02-06-04-010A Date: 6/27/2003 Title: Erratic Fuel Gauge Reading (Reprogram the PCM) Models:
  • 1999-2004 Corvette
  • 2001-2004 Corvette Z06
Summary:
Some owners may comment about the fuel gauge intermittently indicating an empty reading and then return to the correct fuel level indication.
This condition may result when fuel blends containing aggressive sulfur compounds & Ethanol react with the fuel sender assembly, which may result in voltage spikes being induced on the fuel level signal to the PCM.
Use of another fuel blend may reverse this reaction and return the system to normal operation.
Reprogram the PCM with the new service calibration which is available in the June 2003, Techline TIS release sent to the dealers on 6/28/03.
Use the TIS Version 7 or later data update.
 
DeeGee

DeeGee

CCCUK Member
In 20 years with the C5 mine has only done this once.
Back in the US, owners swore by "Techron", a fuel additive that cleaned the sulphur deposits on the senders. I've not managed to find it here but Redex do a similar product. I never allow the tank to drop below 1/4 full so that the senders are always submerged. I also use 99 octane whenever I can. It's worked thus far touch wood.
 
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