Gas Gauge Malfunction

daleharrison · 07-31-2008, 11:50 AM

I have an issue with my gas gauge that I am hoping someone can shed some light. I fill the tank up all the way-the pump shuts off automatically. The gauge shows 3/4 full for the next 50 miles and then shows full. This has happened twice-the first at dealer pick up( and the salesman filled it up with me watching) and then again on the second fill up. Can someone help??

SmarTek-TNG · 08-03-2008, 06:31 AM

I have not had any Smarts with exactly the symptoms you describe, but I can say I have replaced 4 or 5 fuel tank sending units for gas gauge related problems, over the past few months. (I am the smart tech at Germantown, MD). Generally, the cars will come in with a problem like, "my gas gauge is stuck at 3/4 and never goes down even though I have driven 200 miles". Usually I find a fuel gauge sending unit fault code, and replacing the sending unit fixes it. Sometimes just resetting the instrument cluster with the Smart laptop fixes it, but I question whether this is a band-aid that doesn't really address the root problem, so I replace the tank sending unit anyway.

hope this helps

**SmartCard** · 08-03-2008, 06:36 AM

Quote:

Originally Posted by daleharrison

I have an issue with my gas gauge that I am hoping someone can shed some light. I fill the tank up all the way-the pump shuts off automatically. The gauge shows 3/4 full for the next 50 miles and then shows full. This has happened twice-the first at dealer pick up( and the salesman filled it up with me watching) and then again on the second fill up. Can someone help??

I think one other forum member had mentioned about his/her gauge not showing fill at first upon fill up. How does the gauge behave for the rest of the tank?

mfoster · 08-03-2008, 06:39 AM

SmarTek-TNG - Nice to see someone that actually works on the smarts be a member of the forum. Your expertise will be greatly be appreciated.

Smart Enuf · 08-03-2008, 07:29 AM

This happened to me once. "Filled" it up until the nozzle shut off automatically (I always stopped at the first click at that time). As I drove off, I noticed the gas gauge was already down by 1 increment (7/8 tank). About 4 miles down the road, the indicator went back to full. However, after 22 miles, the indicator went back down again to 7/8, then at 48 miles it went down to 6/8.

Near as I can tell, my fill up didn't really fill it up at the first click. Some nozzles can be finicky if the nozzle-gas tank interface at the fill tube isn't perfect (California enhanced vapor recovery equipment), and they can click off prematurely. Thus, it apparently didn't give me a full tank. Not sure why the gauge went back up temporarily; it may have been the slight hill I went up made the fuel tank gauge think it was full temporarily. But it hasn't happened again.

jefferios · 08-03-2008, 07:34 AM

I filled up once and I knew it clicked early, so I started the pump again. I ended up 1.5 gallons more after the click. I do not use that particular pump anymore. Otherwise my gauge has been working well. I usually reach the 1/2 way mark around 210 miles

SuperGeek · 08-03-2008, 07:51 AM

SmartTek - glad to have you here. Mind if I start the cycle of Tech abuse with one more question?

I've noticed, among dozens of others here, that the fuel gauge isn't an exact 1.1-1.2 gallon per bar measurement. I tested mine after the last fillup using my ScanGauge... it went 2.04 gallons and about 60 miles before the first bar went down, another 0.5 gallons (about 15 miles) later the second bar went down. The next day the third one's down, and I don't have more than 100 miles on this tank. It's probably within a one bar range of error now, but that first 60 miles was deceptive.

Does this sound like an actual problem in need of repair? For me, the lack of an accurate gauge isn't a problem because I plan to keep it half full all the time. (I found my reserve gauge, I'm happy now) But to someone else this could be a big issue.

Bum-bling-B · 08-03-2008, 08:36 AM

Yesterday when I stopped by our new dealer I asked of common problems - this was one of the two. Gauge reads 7/8 when tank was just filled. He said in all their cases problem was fixed with the laptop.

On the ride home my first bar went down at 50 miles, next one went at about 90. I normally go about 85 miles before I drop the first bar so I was thinking the previous gas pump clicked off too early. I decided to top off again as to check everything out. Mileage came out to 45mpg - the gauge wasn't where it was supposed to be but the actual fuel in the car was. Of course in my particular case it could also of been a miscalculated pump in my favor for once too.

GoMXracing · 08-03-2008, 10:26 AM

oooh i feel sorry for that Smart tech........

he may of opened a can-o-worms

i am a tech on another line......and i dont think i would of mentioned i work on cars if i were in a forum that is about cars i work on.

SmarTek-TNG · 08-04-2008, 04:56 AM

hehe, I thought about keeping it secret, but for some reason I am drawn to this forum. I am inherantly lazy with emailing and responding to posts, so no offense if it takes me many days to respond. I also think this forum may help me with my job too.. at the least it can give me ideas of what problems people are having and how common they are.

SuperGeek: I haven't really paid too much attention to where the bars are while the tank drains (I don't drive them for long distances), but it does not sound like a problem to me.. I would be surprised if the bars represented perfectly equal amount of fuel.

I should probably say for the record that while I do work on almost every smart that comes to my dealership, the majority of my time is spent on Mercedes, so I definitely do not know everything Smart, and I'm learning all the time.