Fuel Tank Pressure Sensor Diagnosis

Diagnostic Chart:

CIRCUIT DESCRIPTION

The fuel tank vapor pressure sensor is used in order to detect a vacuum decay or an excessive vacuum during the [1][2]EVAP diagnostic routine. The sensor responds to the changes in the fuel tank pressure or vacuum. The signal voltage to the Control Module varies from a minimum of about 0.2 volts with pressure in the fuel tank to above 4 volts with a high vacuum in the fuel tank.

The Fuel Tank Vacuum display on the scan tool has an auto zero feature which occurs at each ignition cycle and is corrected according to the barometric pressure. Because of this, the Fuel Tank Vacuum may not accurately reflect the actual output of the sensor or the conditions within the fuel tank.

The Fuel Tank Vapor Pressure Sensor Diagnosis Table is intended to isolate and diagnose the electrical problems in the sensor wiring or the sensor.

DIAGNOSTIC AIDS

Check for the following conditions:

Inspect the Control Module harness connectors for the following conditions:

- Improper mating.

- Broken locks.

- Improperly formed.

- Damaged terminals.

^ Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Vacuum display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.

Refer to EVAP System Cleaning before starting repairs.

TEST DESCRIPTION

The numbers below refer to the step numbers in the diagnostic table.

1. The Powertrain OBD System Check prompts the technician to do some basic checks and store the Freeze Frame Data and Failure Records in the scan tool if applicable. This creates an electronic copy of the freeze frame data taken when the fault occurred that can be referred to later.

5. A normal fuel tank pressure sensor voltage output with no pressure or vacuum on the fuel system should be between 1.3V and 1.7V.

14. Reprogram the replacement Control Module. Refer to the latest Techline information for programming procedures.