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  #1  
Old 08-19-2010, 10:04 PM
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Question Fuel Gauge Problems

02, F150 4.6L Supercab

Today I stopped to fill up. The gauge read just below 1/4 tank. It held about 22 gallons. I left the key in the accessory position while I filled up so my son could listen to the radio. (Its possible I turned the key back to the on position after I turned it off...) I topped the tank off and reset the trip odometer to check my mileage. When I restarted my truck, the fuel gauge needle fell below empty and the low fuel light came on. I drove home, about 20 minutes and the needle never moved. I ran a couple of errands also later, about 10 - 15 minutes total drive time and it still showed no fuel.

I just went out and checked it noticed that the needle moves up to E when the truck is off, but when I start it, the falls slightly below E.

Any ideas???
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  #2  
Old 08-20-2010, 03:02 PM
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YouR dash is micro processor controlled.
The fuel tank sender is an analog circuit for level indication.
The dash processor converts from analog to digital.
The dash gage is updated 'every so often' so does not follow the level full time.
Seems the dash program has gotten out of register from the ignition switch actions.
Give it more time or power down the truck battery to see if it rests the dash functions. If not you have an issue to be found.
The dash also has a diagnostic program you could check but how to do it and the output info is a bit much to present on this board.
Basicly, you use the trip button to enter diagnostics, then step through the functions to see what they read and go from there.
The readout info is a combination of hex, binary, octal and base 10 , so you would need the info to see what they mean as well as code definitions.
Good luck..
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  #3  
Old 08-20-2010, 03:25 PM
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When I had this problem, it turned out I had a bad connection under my truck.
Like yours, mine came all of a sudden. They ended up replacing one of the pig tails on the sensor.
Possibility for you, but who knows.
That alone was about a $250 fix.
The only thing I could really say is to pull off your battery cables and see if that does anything. If it doesn't, it needs Diagnosis from another source.
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  #4  
Old 08-21-2010, 01:47 PM
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Not sure what happened...

I pulled the negative cable off the battery and left it all night. I reconnected it this morning and also tightened the positive cable.

Cranked the truck and still fuel gauge did not register. I drove the truck about 12-15 miles, stopped to pick up my daughter. When I restarted the truck, the fuel gauge was working, showing completely full.

I had driven the truck close to 1 hour total since the problem first occurred. I read one post that stated it could take up to 55 minutes for the gauge to register a change in the amount of fuel (slosh mode?).

Is this possible? I've had a 99 F150 SC 5.4 4x4, and a 2001 Screw 4x4 5.4L and never had a problem like this.

Thanks!
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  #5  
Old 08-21-2010, 03:11 PM
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Unless there is an intermittant issue, the dash looks at the level signal in time intervals, and changes the display to reflect the new value for each time segment. This also takes care to guard against a slosh reading that would make the gage jump around in level.
It is possible you got this sample process out of register by powering the ignition switch to run as the fill was going on, then to Access postion.
Most of the time there is a built-in reset that also uses a time element to get back to the analog input value and register it on the dash..
It just shows that the software was not taken to lengths to correct everything instantly but on a time basis. In this interval, you might assume there is an issue until is takes care of it'self.
Notice that the gage does not usually climb while refueling like a full time analog system in older vehichles did.
Good luck.
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  #6  
Old 08-21-2010, 05:59 PM
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You need to leave the key OFF when fueling, or you will have problems like this. EVERY time I don't leave it off, the gauge doesn't work for at least 15 minutes.
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  #7  
Old 04-29-2011, 05:45 AM
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Still having problems with the fuel gauge... EVERYTIME, I fill up, the gauge falls to below 'E', and the low fuel light comes on. After driving about 50 miles, the gauge will finally start registering as full. However, I have ran out of gas twice now when the gauge gets down to about 1/4 tank. I've been using the trip odometer to judge when to fill up.

I need to diagnose this issue... Gauge, sending unit, or connection somewhere in between?

Can I access the connections to the sending unit without dropping the tank?
What should the electrical readings bet at the sending unit? Are the voltages/ohms different when it is full versus nearing empty? Can I check the electrical readings at the gauge to narrow this down? Anyone know what these electrical readings should be?

HELP!!!
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  #8  
Old 04-30-2011, 12:33 PM
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Help, anyone???
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  #9  
Old 04-30-2011, 12:50 PM
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Usually a gauge issue is GEM related. Iduno about this one tho. Are you having any other electronic issues, like wipers or maybe your 4x4 SOF switch ?

If not, yea iduno, still could be the GEM. These trucks are known for leaking water on the modules thru a windshield leak. This corrodes the GEM terminals and the gas gauge is one of the problems on the list that can occur.

Could be a bad sender or a bad wire, IF that's all your having problems with. You'll have to chase the wires and test connections to determine.

The old types use to rust in the tank, but not these. So pulling the pump would be last on the list.

What they look like on the pump -

Click the image to open in full size.
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  #10  
Old 04-30-2011, 01:18 PM
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usually easier to pull the bed off then drop the tank on most trucks.

I can't remember where the fuel pump sits in relation to the tank, but if you have a screw, the cab may be too far back and youll have to drop the tank.
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  #11  
Old 04-30-2011, 04:10 PM
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Quote:
Originally Posted by glc View Post
You need to leave the key OFF when fueling, or you will have problems like this. EVERY time I don't leave it off, the gauge doesn't work for at least 15 minutes.
same here
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  #12  
Old 04-30-2011, 09:29 PM
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More info...

Fuel gauge is the only thing giving me problems. I haven't pulled the instrument cluster to check any voltages yet, but I will before I drop the tank. Anyone know what the reading should be at the gauge when the tank is full and when it is empty?
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  #13  
Old 05-06-2011, 10:01 AM
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DTC Code

OK, I located last night where I could enter diagnostic mode on the odometer by holding down the reset button and turning the key to run...

All of the gauges cycle fine...

I'm getting a DTC code - 9202 "Fuel sending unit open?". My local dealer has no info on this code. His main electrical technician was off today.

The fuel sending unit output was 255 on the readout.

The tank is completely full of fuel.

Any ideas or help would be appreciated!
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  #14  
Old 05-06-2011, 03:56 PM
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Here is what I can tell you about the dash code.
It is called a HEC code.
The code is the same as a body code = B1202 and is the same in discription.
Your dealer tech may not know this or forgot. I'm sure they have the info somewhere.
The 255 and all values are an 'octal' number derived from a calculating (analog to digital converter) circuit to keep the fuel gage stable and to be able to light the low fuel lamp when value of 54 is present as well as present diagnostic value assistance.

For your info, here is some fuel level values in a normal working system.
Values:
0-18 = a short ckt.
41 = E mark.
54 = low fuel and light.
93 = 1/4.
138 = 1/2.
178 = 3/4.
215 = full mark.
232 = full stop.
255 = open sender ckt.
Octal numbering system can be converted to Binary or Decimal and is used in digital systems.
The vehichle systems use a mix of all these numbering systems including Hexidecimal.
The dash diagnostics can yield a lot of other info about input and output signals to the dash processor, as you have found.
Good luck.
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  #15  
Old 05-06-2011, 10:12 PM
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255 hec

Bluegrass, does the 255 indicate a problem or is that the "normal" reading when the tank is full?

I've read about the sender harness connectors deteriorating and giving bad readings. The truck came from PA, but it only has 28K miles on it... I'm wondering if there's a bad connection. Is there anyway to check the connectors and the wiring harness without dropping the tank or lifting the bed?

thanks!
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Old 05-06-2011, 10:12 PM


 
 
 
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