Thread: fuel gauge going crazy

Today I put 85 bucks in diesel and turned truck on and gauge dropped below E.. and info button read. --- until Empty and I did the system check and it read fuel data error.. any one know what could be wrong??

MIne did this 2 weeks ago. I was empty and after filling up the truck still showed "e." It took 3 hours and it slowly moved to "f." Got me I thought this was a ful proof system. A floater with a pot that sends a signal to the gague. Got me?

You most likely have a bad sending unit in the tank. I have gone through 2 of them in 72,000 miles both were replaced under warranty - one @ 49K the other at 70K. My first go around it just dropped to zero and never recovered. My second go around it would give me one of three scenarios:

1 - Filled up the tank, read full, within on average 15 minutes it would drop to below E and set off a CEC. It would recover to full within an 1hr and be fine until the next fill up.
2- Just dropped to E during fill up within 1hr or two it would recover until the next fill.
3- Note #1 & 2 were with the engine running - Otherwise with the engine off I could get either of the option above. I could also could clear my code P0460 (Fuel Sending Unit Circuit) it would reset and be fine until I filled up.

Pulled this from another forum I am part of hope it helps explain other things it could be too.

Fuel Gauge

The instrument cluster receives the fuel level signal from the fuel level sensor, part of the fuel tank unit. The fuel level sensor measures variable resistance in the fuel tank depending on the current fuel level. When the fuel level is low, the resistance in the unit is low (15 ohms ± 2 ohms). When the fuel level is high, the resistance in the unit is high (160 ohms ± 4 ohms).

The instrument cluster uses 4 different operating modes to calculate the fuel level:

anti-slosh (default mode)
key OFF fueling
key ON fueling
recovery
After a fuel fill up, the time for the fuel gauge to move from empty (E) to full (F) ranges from 2 seconds to 55 minutes depending on which operating mode the fuel gauge is in.

The default fuel gauge mode is called the anti-slosh mode. To prevent fuel gauge changes from fuel slosh (gauge instability due to changes in fuel sender readings caused by fuel moving around in the tank), the fuel gauge takes approximately 55 minutes to go from full (F) to empty (E).

The key OFF fueling mode (2 seconds to read empty [E] to full [F]) requires 3 conditions be met:

The key must be in the OFF position when refueling the vehicle.
At least 15 percent of the vehicle's fuel capacity must be added to the fuel tank.
The instrument cluster must receive a valid key ON fuel sender reading within 1 second of the key being put into the RUN position. The key ON sample readings are considered valid if the fuel sender reading is between 15 ohms ± 2 ohms and 160 ohms ± 4 ohms. If these conditions are not met, the fuel gauge stays in the anti-slosh mode, which results in a slow to read full (F) event.
The key ON fueling mode (approximately 90 seconds to read empty [E] to full [F]) requires 3 conditions be met:

The transmission is in park (P) (automatic transmissions), or the parking brake applied (manual transmissions).
The key is in the RUN position.
At least 15 percent of the vehicle's fuel capacity must be added to the fuel tank.
In key ON fueling mode, a 30 second timer activates after the transmission is put into the park (P) position (automatic transmissions) or when the parking brake is applied (manual transmissions). When the 30 second time has elapsed and at least 15 percent of the vehicle's fuel capacity has been added, the fuel gauge response time is 90 seconds to read from empty (E) to full (F). When the transmission is shifted out of park (P) or the parking brake is released, the fuel gauge strategy reverts to the anti-slosh mode. This mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.

Recovery mode is incorporated into the instrument cluster strategy to recover from a missing fuel level message during a refueling event. Missing fuel level messages result from intermittent opens in the fuel sender or its circuits. Recovery mode (empty [E] to full [F] approximately 20 minutes) is initiated when the following 2 conditions are met:

The instrument cluster is in the anti-slosh (default) mode.
The actual fuel level in the tank is greater than what is being displayed by the fuel gauge.

Check Engine Light on with P0460 Fuel Level Sensor Code:
This may be caused by a miscommunication of fuel level ststus between the instrument cluster and engine computer. This code is set when the engine computer does not see the fuel level dropping it expects. It may be caused by customer-installed items, such as a remote start system that does not power the dash when activated, an over-sized fuel tank or in-bed fuel tank. If these conditions do not exsist, the engine computer should be reprogrammed using WDS/IDS version 43.4 or higher. This condition can also be caused by fueling with the engine running, parking on an angle, or driving up a long grade. In some cases the fuel level sender may be faulty, or have a sulfur build up on the sender and have code P463(use Chevron Techron Plus Concentrate to correct). TSB 06-13-11

Tim

thanks to ultra low sulfer diesel, the ground wire on the sending units looses its grounding ability. I have dropped my tank twice to fix the problem. The second time the ground wire was actually broken. cheaper than buying a new sending unit.