Circuit Description
The fuel tank pressure sensor responds to changes in the fuel tank pressure or vacuum. This information is used in order to detect vacuum decay or excessive vacuum during the EVAP diagnostic routing. The fuel tank pressure sensor signal voltage to the VCM varies from a minimum of about 0.1 volts with pressure in the fuel tank to more than 4.0 volts with a high vacuum in the fuel tank.
The Fuel Tank Pressure 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 Pressure display may not accurately reflect the actual output of the sensor or the conditions within the fuel tank.
The fuel tank pressure sensor diagnostic table is intended to isolate and diagnose any electrical problems with the sensor wiring or the sensor.
Conditions for Running the DTC
The ignition switch is in the RUN position.
Conditions for Setting the DTC
The fuel tank pressure sensor voltage is more than 4.98 volts for more than 5 seconds.
Action Taken When the DTC Sets
The VCM turns ON the malfunctiuon indicator lamp (MIL) after 2 consecutive driving cycles with the fault active.
Conditions for Clearing the MIL or DTC
| • | The control module turns OFF the MIL after 3 consecutive drive trips when the test has run and passed. |
| • | A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle. |
| • | Use a scan tool in order to clear the DTCs. |
Diagnostic Aids
- Inspect the control module harness connectors for the following conditions:
- Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Pressure 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 Wiring Repairs in Wiring Systems.
| • | Any improper mating |
| • | Any broken connector locks |
| • | Any improperly formed connectors |
| • | Any damaged terminals |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
If the EVAP fuel tank pressure sensor value is less than -16.50 inches H2O, an EVAP Fuel Tank Pressure sensor circuit problem may be present or there may be an internally-shorted fuel tank pressure sensor. Note that -17.32 inches H20 is less than -16.50 inches H20.
-
If the fuel tank pressure sensor value is less than 7.4 inches H2O, the fault is the fuel tank pressure sensor, or the reference voltage is more than 5.00 volts. With good circuits, a disconnected fuel tank pressure sensor should indicate 7.4 inches H2O.
-
A high voltage reading on the 5-volt reference circuit could be caused by a short to voltage on another 5 volt reference circuit. Some 5-volt reference circuits are shared inside and outside the VCM. A defective linear EGR valve may bleed battery voltage onto the 5-volt reference circuit.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: : Before clearing the DTCs, use the scan tool Capture Info to save the Freeze Frame and Failure Records for reference. The control module's data is deleted once the Clear Info function is used. Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||
Is the fuel tank pressure less than the specified value? | -16.50 in. H2O | Go to Diagnostic Aids | ||
Disconnect the FTP sensor electrical connector. Is the pressure more than the specified value? | 7.0 in H2O | |||
4 | Using a digital multimeter (DMM), measure the voltage on the 5-volt reference circuit at the FTP sensor connector. Is the voltage more than the specified value? | 5.20 V | ||
5 | Using the DMM in order to measure the voltage between the fuel tank pressure sensor signal circuit and ground. Is the voltage more than the specified value? | 0.5 V | ||
6 | Repair the short to voltage in the FTP sensor signal circuit. Is the repair complete? | -- | -- | |
Repair the short to voltage in the 5-volt reference circuit. Is the repair complete? | -- | -- | ||
8 |
Was terminal contact repaired? | -- | ||
9 | Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement Is the replacement complete? | -- | -- | |
10 |
Was terminal contact repaired? | -- | ||
11 |
Important: : The replacement VCM must be programmed. Replace the VCM. Refer to VCM Replacement/Programming . Is the action complete. | -- | -- | |
12 |
Does the scan tool indicate the diagnostic Passed? | -- | ||
13 | Does the scan tool display any additional undiagnosed DTC's? | -- | Go to the applicable DTC table | System OK |
