Test B: Incorrect Fuel Gauge Indication
PINPOINT TEST B: INCORRECT FUEL GAUGE INDICATIONNormal Operation
The fuel tank is a saddle tank design with variable resistance senders in each side of the tank. The fuel pump module and the fuel sender are driven by floats that provide resistances related to the fuel level on each side of the tank to the smart junction box (SJB). The fuel pump module and the fuel sender uses an approximate resistance range between 15 ohms ± 2 ohms at empty (E) and 160 ohms ± 4 ohms at full (F). The fuel pump module is hardwired to the SJB through the signal circuit 1356 (LG/VT) and the return circuit 1357 (LB/YE). The fuel sender is hardwired to the SJB through the signal circuit 29 (YE/WH) and the return circuit 1357 (LB/YE). The SJB monitors the resistance readings that are sent to the SJB from the fuel pump module and the fuel sender and sends the instrument cluster (IC) a message over the communication network to command the fuel gauge with a corresponding movement of the pointer. If the fuel sender is open, the fuel gauge defaults to the fuel pump sender value only and the fuel gauge indicates E to 1/2 tank. If the fuel pump sender is open, the fuel gauge defaults to the empty position.
The instrument cluster (IC) uses 4 different operating modes to calculate the fuel level:
- Key OFF fueling
- Anti-slosh (default mode)
- 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.
Key Off Fueling Mode
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 (IC) 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.
Anti-Slosh Mode
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).
Key On Fueling Mode
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% 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% 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. The key ON fueling mode prevents slow to read full events from happening if the customer refuels the vehicle with the key in the RUN position.
Recovery Mode
Recovery mode is incorporated into the instrument cluster (IC) strategy to recover from missing fuel level inputs 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 (IC) 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.
Instrument Cluster (IC) DTCs:
Smart Junction Box (SJB) DTCs:
PCM DTCs:
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Fuel pump module
- Fuel sender
- SJB
- Fuel tank
- Instrument cluster (IC)