DP Dave

Yesterday strange things began to happen immediately after filling the car with fuel.
1. Filled the car with 91 octane (live in CA and this is the highest available).
2. The fuel nozzle automatically shut off so I thought the car was full. I don't like to "top off" and after reading I learned not to overfill.

Then thing began to happen

The gauge would drop to "empty" and the DIC would read "Service Fuel System". I shut down the car and removed and replaced the gas cap. No help, same thing!

Drove the car to burn off some gas, filled up and then realized I had not previously filled the car. Perhaps 3/4 full.

Stopped and then filled the car. Gauge went to "full", thought all was okay then it started again!

Owners manual says "check engine" light will stay on for the duration of a full tank of gas to burn off before the light will go off.

A couple of questions/thoughts

1. Got bad gas when I filled up.
2. Drive to burn off gas to make room for #3
3. Add Octane Boost from local auto parts?
4. Drive to deplete Octane Boost gas.

Thanks

JUST DROVE THE CAR AND EVERYTHING SEEMS TO BE BACK TO NORMAL. My guess is that it was some "bad" gas" and that the fill up may have diluted it. I will keep my fingers crossed.



UPDATE
Took car to the dealer
1. Bad sending unit, will have to order from Lansing as none are to be found in So. CA.
2. Okay to drive car, just keep fuel in it!

cam30era

Same thing happened to me in September, when my car had 1100 miles on it. After doing everything that you did, and adding a couple of bottles of Techron, the problem persisted. Took it to the dealer. They read the trouble codes and diagnosed a defective fuel sending unit (FSU). After replacement, car has been trouble free.

James Shearer

DP Dave This has been a huge problem with the C5 (mine included). Mine went whacky several times, then would work fine for awhile. Some have blamed the gas-I don't buy that theory. The dealer will replace the sending unit-but that's no long term fix. Can't imagine its the same problem with the C6!! I've learned to always reset the trip odometer so I can monitor the miles after each fill up--geez, why should we have to worry about the gas gauge?!?

DP Dave

Thanks,
I will take it to the dealer in the morning!

vetteship

Please don't tell me the C6 is also plagued with gas gage reading problems like my C5, I was looking forward owning a C6 without this irritation

Mark S.

Once I switched from Amoco/BP to Shell/Texaco, the fuel gauge problems went away in my C5...

andreas g.

same thing happed to my C6. trouble code said sending unit bad. Need to replace it

andy G

DP Dave

Just dropped the car off at the dealer! Now to wait and see!

cam30era

Good luck! In spite of the negative experience of some forum members, I must say that it has been 4 months and 3,000 miles of trouble free motoring since the repair.

sdvetter

You're not alone, it happened to me too at 700 miles. FSU is being replaced as we speak. I hope it does the trick. Obviously a problem. See the General discussion forum for other posts on this matter. Service manager told me replacement FSU had gold tipped sensors. Don't know if that is true and if true whether is should make a difference. I asked about the gas and he said the gas only makes a difference to performance. If you use generic 91 octane like from Costco or Arco you'd likely loose performance at the high end, but it should have no impact on the FSU sensors. He did say it would not be a bad idea to fuel every few tanks with branded gas like Chevron to help keep the injectors clean.

JFTaylor

Ensure that you tighten the gas cap. 3-5 clicks should do it.

andreas g.

just talked to my tech that's going to do my car. He said that it's basicly contaminated gas,and that they see alot of it in the western U.S. I use chevron and shell and still have the problem. Interesting though I didn't have the problem with my C5, and I buy my gas at the same place. Also mine seems to go bad after I've driven it for more than an hour.

Andy G.

DP Dave

Well,
I picked up the car and to my surprise everything is okay. I will drive it until Monday when I have an appointment for the sending unit to be replaced. By then I will have a chance to see if it acts up again.

AS TO THE Forum Member who suggested the gas be tightened to 3 clicks - thanks however I tried that a couple of times, no help.

JoesC5

Welcome to the world of owning a C5---- sorry, I mean a C6. Blaming the problem on bad gas is BS. The problem was (is) with the sorry engineering design of the fuel tank(s) sensor(s). That was the problem with the C5 and it appears it may continue to haunt the C6. If it was bad gas, every owner of every make and model of car would be screaming bloody murder. One instance of bad gas in Flordia does not make it a nationwide problem as some seem to think. It's a design problem, plain and simple. Had it repaired twice on my C5, but never a problem with my Buick, or my 56 or my 64 vettes with original gas tank sensors, or with any car Iv'e ever owned. Only with my C5. If it takes the use of an aftermarket gas treatment or the use of only one brand of gas to avoid the problem then GM should supply the owners with a lifetime supply, at no cost, of such. And while I'm on a rant, steering wheel column locks have been on every car since 1969, but only with the C5, and I've heard reports with some C6's, have the y been a problem that would leave you stranded. And the only instance that I'm aware of that a manufactor has had to have a full recall to correct the problem was with the C5. Well, not completely corrected, the poor owners of 6-speeds can still experience the problem.

I remember when the owners of C5's were having the leather seat covers showing wear after only a couple of thousand miles. GM blaimed it on the owners, saying they were entering and exiting their cars improperly, plus the wearing of jeans was the problem. After enough bitchin' they did replace the covers under warranty, including mine, with covers made of vinyl in the area showing the wear. Purchase leather, end up with plastic. Typical GM.

Lerxst2112

Ditto, except that I don't think the ROFL smiley is the one I'm looking for. More along the lines of "smash the head of the engineer who didn't fix this @#$!#% thing".

Where's that one?

I also do the trip B reset every fill-up. And shouldn't have to!!!!!!

LS WON

The pump will click before tank is full then I have to hand pump it.
I also notice that after the low fuel warning light comes on in the DIC that I have about 5 gallons left. I find that when I top off the gas after the pump stops and clicks I can get another 3 gallons in there.

shopdog

Your older cars used a mechanical moving float assembly attached to an arm which rotated a potentiometer. It didn't care what liquid was in the tank, gas, water, alcohol, all the same to it. The C5/C6 use a pair of stationary silver electrodes to measure the electrical resistance of the fuel. The more of the electrodes the fuel covers, the lower the resistance.

The newer system has no moving parts to wear out, no float to fill with fuel and sink, and can measure the amount of alcohol or MTBE in your fuel (something the ECU wants to know so it can make adjustments for these oxygenates in the fuel) by pulsing the current through the electrodes in a certain way and noting the changes in resistance. This is actually pretty slick, but requires a microprocessor to control it and interpret the readings.

The new system's electrodes can become contaminated, same principle as the catalyst becoming contaminated in the cat converters. When that happens, the system quits working, or works erratically. Also like the catalyst, this contamination is a fuel problem. In the case of the catalyst, it was lead in the fuel. In the case of these fuel sensors, it is sulfur in the gas. This is one of the reasons GM worked to set up the Top Tier fuel supplier rating system. To be Top Tier certified, a supplier has to guarantee the sulfur content of the fuel falls below a certain percentage (there's more to Top Tier than that, but that is one of the requirements).

But, you are right that it is a design issue too. GM chose to use silver electrodes instead of gold or platinum. The latter don't react with sulfur, but they require a higher voltage to work correctly to detect the percentage of oxygenates in the fuel. So not only would it have cost GM more to use the more expensive metals for the electrodes, but GM would also have had to add a DC to DC step up module to provide the higher voltage required to operate those electrodes, and a higher voltage A/D converter to interface to the microprocessor. That would raise costs too, and possibly create a safety hazard as well. So they depended on the fuel suppliers to get the sulfur out instead.

GM's decision was not too unreasonable considering that the EPA is also telling the fuel suppliers to get the sulfur out for other reasons, ie to reduce SO2 emissions. But a lot of the fuel we consume today comes from foreign refineries who may not adhere very closely to the low sulfur mandate. (Can't build new refineries here because environmental laws have become too strict, so gasoline refining is moving more and more off shore, and outside of the direct control of our regulatory bodies.) The result is we don't always get gas that's of the quality required to operate correctly with the silver sensors.

jimman

High sulfur content, although still a pain when it happens. Been through 5 systems on my C5's before I changed gas. This is what it looks like:

C5 CU

problem is GM sending unit and /or programing ... not contaminated gas. If that was the case Tech would be draining fuel system.