GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Geo 🢒 1996 🢒 Tracker - 4WD 🢒 Engine 🢒 Engine Controls - 1.6L 🢒 DTC P0450 Fuel Tank Pressure Sensor Circuit

Schematic Reference: Engine Controls Schematics

Circuit Description

The fuel tank pressure sensor responds to changes in fuel tank pressure or vacuum. The fuel tank pressure sensor signal voltage to the engine control module (ECM) varies from above 4 volts, with pressure in the fuel tank, to a minimum of 0.6 volts with a high vacuum condition in the fuel tank (vent solenoid closed).

Conditions for Setting the DTC

Input range check:

    • Voltage less than 0.5 volts.
    • Voltage greater than 4.8 volts.
    • Condition present for 0.5 seconds.

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
    • The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC
    • The MIL will turn off after three consecutive drive cycles without a fault present.
    • A DTC will clear after 40 consecutive warm-up cycles without a fault.
    • The DTCs can be cleared by using a scan tool or by disconnecting the ECM battery feed.

Diagnostic Aids

Check for any of the following conditions:

    • A plugged sensor air vent hole. Inspect the sensor and clean if necessary.
    • If multiple DTCs are set, it may be possible to have an open or a shorted reference voltage circuit or an open ground circuit.

An intermittent malfunction may be caused by a fault in the fuel tank pressure sensor circuit. Inspect the wiring harness and components for any of the following conditions:

    • Backed out terminals.
    • Improper mating of terminals.
    • Broken electrical connector locks.
    • Improperly formed or damaged terminals.
    • Faulty terminal to wire connections.
    • Physical damage to the wiring harness.
    • A broken wire inside the insulation.
    • Corrosion of electrical connections, splices, or terminals.

If the DTC P0450 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. Determine if a fault is present. Review the Freeze Frame data to determine the condition of when the DTC set. Always record this information.

    3.

  3. Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes. This also checks the sensor signal input circuit.

    4.

  4. Checks the operation of the tank pressure control valve. For additional functional checks, Refer to Enhanced EVAP System Diagnosis.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

  1. Turn OFF the ignition.
  2. Remove the fuel filler cap.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Select the fuel tank pressure sensor parameter on the scan tool.

Is the scan tool display within the specified value?

0.0-0.9 mm Hg (0.0-0.5 in H2O)

Go to Step 11

Go to Step 3

3
  1. Remove the fuel tank. Refer to Fuel Tank Replacement.
  2. Remove the fuel tank pressure sensor from the fuel tank.
  3. Visually inspect the sensor air vent hole and the air pressure inlet passage for clogging.

Was any problem found?

--

Go to Step 13

Go to Step 4

4
  1. Turn ON the ignition, leaving the engine OFF.
  2. Disconnect the fuel tank pressure sensor electrical connector.
  3. Measure the voltage at the fuel tank pressure sensor terminal 3 (harness side), using a DMM

Is the voltage at specified value?

5.0 volts

Go to Step 6

Go to Step 5

5
  1. Check for an open in the 5 volt reference circuit between the fuel tank pressure sensor and the ECM.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 14

6

Probe terminal 2 of the fuel tank pressure sensor (harness side), using a test light connected to B+.

Does the test light illuminate?

--

Go to Step 8

Go to Step 7

7
  1. Check for an open in the sensor ground circuit between the fuel tank pressure sensor and the ECM.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 14

8
  1. Reconnect the fuel tank pressure sensor electrical connector.
  2. Backprobe the fuel tank pressure sensor connector terminal 1 with the positive lead and connect the negative lead to ground, using the DMM.
  3. Measure the voltage with the DMM set to the DC scale and compare to the specified value.

Was the voltage measured within the specified value?

2.0 to 2.7 volts

Go to Step 9

Go to Step 15

9

Apply a small amount of vacuum to the fuel tank pressure sensor while observing the DMM.

Did the voltage drop when the vacuum was applied?

--

Go to Step 10

Go to Step 16

10

  1. Check for an open in the fuel tank pressure sensor signal circuit between the fuel tank pressure sensor and the ECM.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 14

11

Caution: Do not breathe the air through the EVAP component tubes or hoses. The fuel vapors inside the EVAP components may cause personal injury.

Important: There will be some resistance, but air should flow steadily.

  1. Remove the fuel tank pressure control valve.
  2. From the canister port, blow through the valve.

Does air flow through the valve to the tank port side?

--

Go to Step 12

Go to Step 17

12

Important: The fuel tank pressure control valve will not allow air to flow from the tank side port to the canister side port until the pressure on the tank side is greater than 3.5 kPa (0.5 psi).

  1. From the tank side port, blow hard through the valve. Air should flow through the valve to the canister port.
  2. Using a hand held vacuum pump, apply the specified value of vacuum to the vacuum port of the fuel tank pressure control valve.
  3. With the vacuum applied, blow gently through the tank side port. Air should flow easily through to the canister port.

Does the fuel tank pressure control valve pass both checks?

15 in Hg

Go to Diagnostic Aids

Go to Step 17

13

Clean the sensor air passage(s).

Is the action complete?

--

Go to Step 18

--

14

Replace the ECM. Refer to Engine Control Module Replacement.

Is the action complete?

--

Go to Step 18

--

15
  1. Check for a short in the fuel tank pressure sensor signal (input) circuit between the fuel tank pressure sensor and the ECM.
  2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 18

Go to Step 16

16

Replace the EVAP tank pressure sensor. Refer to Evaporative Emission Tank Pressure Control Solenoid Valve Replace.

Is the action complete?

--

Go to Step 18

--

17

Replace the fuel tank pressure control valve. Refer to Fuel Tank Pressure Control Valve Replacement.

Is the action complete?

--

Go to Step 18

--

18
  1. Perform the scan tool Clear DTC Information function and road test the vehicle within the Freeze Frame conditions that set the DTC.
  2. Review the scan tool data and check for DTCs. The repair is complete if no DTCs are stored.

Are any DTCs displayed on the scan tool?

--

Go to the Applicable DTC Table

System OK