Test B: Incorrect Fuel Gauge Indication

PINPOINT TEST B: INCORRECT FUEL GAUGE INDICATION

NOTE: On gasoline equipped vehicles, the fuel pump module may also be called the fuel tank unit.

Normal Operation
The fuel pump module (gasoline) or fuel level sensor (diesel) is hardwired to the instrument cluster (IC) between the signal circuit 29 (YE/WH) and the return circuit 651 (BK/YE). The instrument cluster (IC) provides a reference voltage to the fuel pump module (gasoline) or fuel level sensor (diesel) on circuit 29 (YE/WH). As the fuel level changes, a float actuates a variable resistor that alters the fuel level signal voltage. The instrument cluster (IC) monitors the changes in voltage and commands the fuel gauge with a corresponding movement of the pointer.

The fuel level sensor 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 low (15 ohms ± 2 ohms). When the fuel level is high, the resistance in the unit is high (160 ohms ± 4 ohms).

On flex-fuel vehicles, basic fuel level indication is the same as gasoline and diesel vehicles, except that the flex-fuel vehicles incorporate the use of a flex-fuel module. The flex-fuel module and converter harness is a DC-AC interface, used to prevent chemical reactions created by the interaction of DC current with the fuel. The flex-fuel module is mounted in the fuel pump module jumper harness (between the vehicle wiring harness and the fuel pump module) and is installed as an assembly. The flex-fuel module receives voltage on circuit 640 (RD/YE) and is grounded through circuit 651 (BK/YE).

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 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 OFF Fueling Mode
The key OFF fueling mode (2 seconds) to read empty
- 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.

Key ON Fueling Mode
The key ON fueling mode (approximately 90 seconds) to read empty
- 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. 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 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 message during a refueling event. Missing fuel level messages result from intermittent opens in the fuel sender or its circuits. Recovery mode (empty
- 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.

When the fuel gauge reads approximately 1/16th of a tank, the instrument cluster (IC) illuminates the low fuel warning indicator.

Instrument Cluster (IC) DTCs (Part 1):

Instrument Cluster (IC) DTCs (Part 2):

PCM DTCs:

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

B1-B2:

B2-B4:

B4-B5:

B5-B6:

B7-B10:

B10 Continued:

B11-B13:

B13-B14: