Test B: Incorrect Fuel Gauge Indication
PINPOINT TEST B: INCORRECT FUEL GAUGE INDICATIONB1-B2:
B3-B5:
B6-B8:
B8-B9:
B10-B12:
B12-B14:
B14-B15:
B16-B19:
B19-B21:
Normal Operation
The instrument cluster receives the fuel level inputs from the fuel level sensor, part of the fuel pump module and the fuel level sender. The fuel level sensor and the fuel level sender 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 high. When the fuel level is high (10 ohms ±2 ohms), the resistance in the unit is low (180 ohms ±4 ohms). The instrument cluster provides a reference voltage to the fuel pump module through circuit VMC11 (YE/VT) and the fuel level sender through circuit VMC23 (GN/OG). The instrument cluster receives the return signal from the fuel pump module through circuit RMC32 (GN/BU) and the fuel level sender through circuit RMC33 (WH/VT). As the fuel level changes, a float actuates a variable resistor that alters the fuel level signal voltage. The instrument cluster interprets this signal and commands the fuel gauge to sweep to the correct level.
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 when refueling 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 10 ohms ±2 ohms and 180 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% 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 is incorporated into the instrument cluster strategy to recover from a missing fuel level input after 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.
DTC B1202 - is a continuous and on-demand DTC that sets in the instrument cluster if the instrument cluster detects that the fuel sender is out of range on input circuit VMC11 (YE/VT) with an open or short to voltage. The instrument cluster defaults the fuel gauge to empty (E), once the instrument cluster detects a fault and sets DTC B1202.
DTC B1204 - is a continuous and on-demand DTC that sets in the instrument cluster if the instrument cluster detects that the fuel sender is out of range on input circuit VMC11 (YE/VT) with short to ground. The instrument cluster defaults the fuel gauge to empty (E), once the instrument cluster detects a fault and sets DTC B1204.
DTC B2627 - is a continuous and on-demand DTC that sets when the instrument cluster detects an open or a short to voltage on the fuel level sender signal circuit. The instrument cluster defaults the fuel gauge to empty (E), once the instrument cluster detects a fault and sets DTC B2627.
DTC B2628 - is a continuous DTC that sets when the instrument cluster detects a short to ground on the fuel level sender signal circuit. The instrument cluster defaults the fuel gauge to empty (E), once the instrument cluster detects a fault and sets DTC B2628.
NOTE: Normal operation of the fuel delivery system allows the remote side of the fuel tank (the side opposite of the fuel filler hose) to have less fuel than the side with the fuel pump module (side with the fuel filler hose).
DTC B2879 - is a continuous DTC that sets when the instrument cluster detects a large discrepancy in the amount of fuel (based on input from the fuel senders) between both sides of the fuel tank. The fuel level in the fuel level sender side of the fuel tank (the side opposite the fuel filler hose inlet) has significantly more fuel than the fuel pump module side (the side with the fuel filler hose inlet).
Possible Causes
- Circuitry
- Fuel pump module assembly
- Fuel level sensor
- Fuel level sender
- Fuel tank
- Instrument cluster