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Fuel gauge may be the problem, but may also be a short in wires going to fuel gauge Battery power goes to gauge in dash then to resistor in tank to ground. If the wire going to tank is shorted to frame it will always read full. Test this by disconnecting the wire going to the tank. If it goes to empty then you know the reason, either resistor in tank is bad or wire shorted. .
sending unit on fuel pump is bad, the sending unit shorts out gauge will go to empty or full, never read right, turn on switch ,it goes to full or empty, ,check the pump,hope this helps,thanks robert b.
This is a normal concern.
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 empty (E) to full (F).
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 throughout the entire refueling of the vehicle. At least 15% 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). The key is in the RUN position. At least 15% 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). When the 30-second time has elapsed and at least 15% 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), the fuel gauge strategy reverts to the anti-slosh mode. The key on refueling 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 input during a refueling event. Missing fuel level inputs 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
You don;t say whether the fuel gauge is reading accurately, or whether it's always on empty. If the gauge is always showing empty, it's most likely a problem with the sending unit in the fuel tank. Check the resistance across the two terminals of the sending unit.
On a C900, the fuel sender level unit is separate from the fuel pump
and located on the right side top of the tank, accessible by removing
the trunk floor lift up panel (the pump is located on the left side top
of the tank. Possible problems are: electrical line off or broken, float not working (it's fairly delicate); or gauge not working.
the resistance of the sending unit with the lines disconnected, the resistance should be
2.6 to 3.8 ohms full tank, 63.3 to 67.5 ohms empty tank; and test for
voltage across the top of the sender unit, if no voltage, that's likely
If the gauge is otherwise reading accurately (showing 'full' for a full tank, etc) then the problem is likely a gauge malfunction and can be simply replaced.