GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 Sonoma Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 Fuel Tank Pressure Sensor Diagnosis

Circuit Description

The fuel tank vapor pressure sensor is used in order to detect a vacuum decay or an excessive vacuum during the 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 Evaporative Emission 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.

    2.

  2. 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.

    3.

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

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2
  1. Disconnect the fuel tank pressure sensor electrical connector.
  2. Using a DVM, measure the voltage between the 5 volt reference circuit and the sensor ground circuit at the fuel tank pressure sensor harness connector.

Is voltage near the specified value?

5 V

Go to Step 5

Go to Step 3

3

Check the 5 volt reference circuit for a poor terminal connection at the Control Module.

Was a problem found?

--

Go to Step 11

Go to Step 4

4

Check for an open 5 volt reference circuit to the fuel tank pressure sensor harness connector.

Was a problem found?

--

Go to Step 10

Go to Step 8

5

  1. Remove the fuel cap.
  2. Using the correct test adapter from J 35616 connector test adapter kit, connect a jumper between terminal A at the fuel tank pressure sensor pigtail and terminal A at the harness connector (Control Module side).
  3. Connect a second jumper between terminal C at the fuel tank pressure sensor pigtail and terminal C at the harness connector (Control Module side).
  4. Using a DVM, measure voltage at terminal B at the fuel tank pressure sensor pigtail.

Is voltage between the specified values?

1.3-1.7 V

Go to Step 6

Go to Step 13

6
  1. Check the fuel tank pressure sensor signal circuit for a poor terminal connection at the Control Module.
  2. Repair as necessary. Refer to Wiring Repairs .

Was a repair necessary?

--

Go to Step 11

Go to Step 7

7
  1. Check the fuel tank pressure signal circuit between the fuel tank vapor pressure sensor connector and the Control Module for an open, short to ground, or short to voltage.
  2. Repair as necessary. Refer to Wiring Repairs .

Was a repair necessary?

--

Go to Step 12

Go to Step 14

8
  1. Check the sensor ground circuit for a poor terminal connection at the Control Module.
  2. Repair as necessary. Refer to Wiring Repairs .

Was a repair necessary?

--

Go to Step 11

Go to Step 9

9

Check for an open in the sensor ground circuit.

Was a problem found?

--

Go to Step 12

Go to Step 14

10
  1. Check for a poor circuit terminal connection at the fuel tank pressure sensor connector.
  2. Repair as necessary. Refer to Wiring Repairs .

Was a repair necessary?

--

Go to Step 11

Go to Step 13

11

Replace the faulty harness connector terminals as necessary. Refer to Wiring Repairs .

Is the action complete?

--

Go to Evaporative Emission Control System Diagnosis

--

12

Locate and repair open or short circuit in wiring harness as necessary. Refer to Wiring Repairs .

Is the action complete?

--

Go to Evaporative Emission Control System Diagnosis

--

13

Replace the fuel tank pressure sensor. Refer to Diagnostic Aids. Refer to Fuel Tank Pressure Sensor Replacement .

Is the action complete?

--

Go to Evaporative Emission Control System Diagnosis

--

14

  1. Replace the VCM.
  2. Program the new VCM. Refer to VCM Replacement/Programming .
  3. Perform the VTD Password Learn Procedure. Refer to Password Learn .
  4. Perform the CKP System Variation Learning Procedure. Refer to Crankshaft Position System Variation Learn .

Is the action complete?

--

Go to Evaporative Emission Control System Diagnosis

--