Test C: Incorrect Fuel Gauge Indication

PINPOINT TEST C: INCORRECT FUEL GAUGE INDICATION

Normal Operation
The fuel pump module and the secondary fuel level sensor receive a reference voltage signal from the instrument cluster (IC) through circuits VMC11 (YE/VT) and VMC23 (GN/OG) respectively, and returns the fuel level signal to the instrument cluster (IC) through circuits RMC32 (GN/BU) and RMC33 (WH/VT) respectively. As the fuel level changes in each side of the fuel tank, a float actuates a variable resistor that alters the fuel level signal voltage. The instrument cluster (IC) interprets these signals and commands the fuel gauge to sweep to the correct level.

NOTE:
- The fuel pump module may also be called the fuel tank unit.
- The secondary fuel level sensor may also be called the fuel level sensor.

The fuel tank is a saddle tank design with 2 variable resistance senders, driven by floats, that provide resistances related to fuel height, in each side, to the cluster through hardwired inputs. The fuel level is read from each fuel sender through a 2-wire input. The fuel senders provide variable resistance between 180 ohms ± 4 ohms (empty tank) and 10 ohms ± 2 ohms (full tank). If the fuel level is low, the resistance in the fuel level sensor is high, causing the gauge to indicate empty (E). When the fuel level is high, the resistance in the fuel level sensor is low, and the gauge indicates full (F).

As fuel is consumed from the fuel pump module side of the fuel tank (the side with the fuel filler hose inlet), fuel is transferred from the secondary fuel level sensor side of the tank (the side opposite the fuel filler hose inlet) to the fuel pump module side of the tank. The fuel pump module is connected to the secondary fuel level sensor by a crossover line and transfers fuel when the fuel pump module is running.

The instrument cluster (IC) 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.

Anti-Slosh Mode
The default fuel gauge mode is 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 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 during 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 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.

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 transaxle is in PARK (P) (automatic transaxle), or the parking brake is applied (manual transaxle).
- 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 transaxle is put into the PARK (P) position (automatic transaxle) or when the parking brake is applied (manual transaxle). 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 transaxle 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 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 (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:

PCM DTCs (Part 1):

PCM DTCs (Part 2):

This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- Fuel pump module assembly
- Secondary fuel level sensor
- Fuel level sensor (float and card)
- Fuel tank
- Instrument cluster (IC)

C1-C2:

C3-C5:

C6-C8:

C8-C9:

C10-C12:

C12-C14:

C14-C15:

C16-C19:

C19-C21: