Fuel Gauge

WARNING: This page is about a different car, the 2005 Lincoln LS. However, it is still accessible from the selected car via links, so may be relevant.

The fuel gauge system has a saddle-type fuel tank with 2 integrated fuel senders: the fuel delivery module and the jet pump module. The fuel delivery module is located on the right side of the fuel tank, and the jet pump module is located on the left side of the fuel tank. The fuel level status is sent directly to the REM, which is hardwired to the fuel senders. The REM sends the fuel data to the instrument cluster via the communication network. Normal operating range of the fuel delivery module is from 15 +/- 2 ohms at empty (E) to 160 +/- 4 ohms at full (F). The normal operating range of the jet pump module sender is from 19 +/- 2 ohms at empty (E) to 160 +/- 2 ohms at full (F). If either the REM or the jet pump module fuel sender has an open or shorted signal, the instrument cluster logs diagnostic trouble code (DTC) B1201. If the jet pump module sender is open, the fuel gauge defaults to the fuel delivery module sender value only and the fuel gauge indicates E to 1/2 tank (depending on the fuel level on the fuel delivery module side of the tank). If the fuel delivery module is open, the fuel gauge defaults to the empty position.

NOTE: It is critical to follow the pinpoint test diagnostic methods to make sure the correct mode is being used during diagnostics.

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 is 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) (automatic transmissions), or the parking brake is released (manual transmissions), 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.