Circuit Description
The DTC P0450 Fuel Tank Pressure (FTP) Sensor Circuit diagnostic monitors the fuel tank pressure sensor voltage. The evaporative emission (EVAP) control system prevents the emission of the fuel vapors. The fuel vapor generated in the fuel tank while driving or idling enters the EVAP canister where a charcoal element absorbs and stores the fuel vapor. When certain engine operating conditions are met the powertrain control module (PCM) purges the EVAP canister of stored vapors by turning ON the EVAP canister purge valve.
Emissions laws require that the PCM detect any leakage within the EVAP system. The PCM monitors the EVAP system for leaks by controlling and observing the vapor pressures in the EVAP system. The FTP sensor is used to detect any unexpected pressure in the EVAP system. The PCM supplies a 5-volt reference, an electrical ground, and a signal return circuit that has a 5-volt bias. The FTP sensor contains a silicon based chip that changes electrical resistance when pressure is applied. The sensor converts the positive or the negative pressure into an electrical signal and sends the signal to the PCM.
Fuel Tank Vapor Space | FTP mmHg | FTP Signal Voltage |
|---|---|---|
Pressure | Positive Value | High |
No Pressure | Near Zero | 3.0-3.6V |
Vacuum | Negative Value | Low |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0450 Fuel Tank Pressure (FTP) Sensor Circuit
Conditions for Running the DTC
| • | The engine has been running less than 10 seconds. |
| • | DTC P0450 runs once per drive cycle when the above conditions have been met. |
Conditions for Setting the DTC
| • | The FTP sensor signal indicates less than -30.48 mm Hg (16.3 in H2O) for 7 seconds. |
| OR |
| • | The FTP sensor signal indicates more than 15.24 mm Hg (8.16 in H2O) for 7 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL). |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after 3 consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function. |
Diagnostic Aids
| • | If a DTC P0450 is intermittent, road test the vehicle while observing the fuel tank pressure sensor with a scan tool. A momentary reading of less than 0.20 volts may indicate an intermittent short to ground in the sensor input circuit. A momentary reading of more than 4.50 volts may indicate an open in the sensor input or ground circuit. |
| • | The EVAP system diagnostic can be monitored on the scan tool under the I/M System Information selection. When the EVAP test displays a YES status, indicating that the system diagnostic is completed, check for DTC P0450 in the Last Test Failed screen of the scan tool. If there is no DTC P0450 displayed the EVAP system diagnostic has run and passed, indicating that no malfunction was present this time. DTCs MUST be cleared in order to view the Current Status of the system diagnostics being performed. Do not forget that the I/M System Information tests only indicate that the test has run, not if the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved. Refer to Inspection/Maintenance Evaporative Emission System Set . |
An intermittent malfunction may be caused by a fault in the sensor electrical circuit. Inspect the wiring harness and the components for an intermittent condition. Refer to Intermittent Conditions .
The information included in the Freeze Frame data can be useful in determining the vehicle operating conditions when the DTC first set.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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The Diagnostic System Check - Vehicle 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.
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This step determines if a FTP sensor malfunction is present. The input signal of the FTP sensor should indicate atmospheric pressure with the fuel tank filler cap removed. The fuel tank pressure sensor voltage will vary with atmospheric pressure. A typical FTP reading at sea level is between 3.5-3.8 volts.
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This step determines if DTC P0450 is the result of a hard failure or an intermittent condition. Operating the vehicle in the Check Mode enhances the diagnostic capabilities of the PCM.
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This step checks whether there is trapped negative or positive pressure at the FTP sensor.
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This step checks for an open or a short in the FTP sensor 5-volt reference.
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The FTP sensor signal circuit carries a 5 volt bias that can be measured with the DMM. If the voltage is near zero there is an open, a short to ground, or a faulty PCM.
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This step checks for an open in the FTP sensor ground circuit.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | ||||
Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | ||
Is the FTP sensor within the specified range? | 3.5-3.8 V | Go to Step 3 | Go to Step 4 | |
Does DTC P0450 set? | -- | Go to Step 6 | Go to Diagnostic Aids | |
Is the FTP sensor within the specified range? | 3.5-3.8 V | Go to Step 5 | Go to Step 6 | |
5 | Repair the cause of the trapped vapor pressure in the fuel tank. Is the action complete? | -- | Go to Step 14 | -- |
Does the voltage equal the specified value? | 5.0 V | Go to Step 7 | Go to Step 8 | |
Measure the voltage from the FTP sensor input circuit on the harness side using a DMM. Is the voltage near the specified value? | 4.9 V | Go to Step 10 | Go to Step 9 | |
8 | Repair the open in the reference voltage circuit of the FTP sensor between the sensor and SP108. Refer to Wiring Repairs . Is the action complete? | -- | Go to Step 14 | -- |
9 |
Was a repair necessary? | -- | Go to Step 14 | Go to Step 13 |
Probe the FTP sensor ground circuit on the harness side with a test lamp connected to B+. Does the test lamp illuminate? | -- | Go to Step 12 | Go to Step 11 | |
11 | Repair the open in the ground circuit of the FTP sensor between the sensor and SP108. Refer to Wiring Repairs . Is the action complete? | -- | Go to Step 14 | -- |
12 | Replace the FTP sensor. Refer to Evaporative Emission System Vacuum Leak Pump Replacement . Is the action complete? | -- | Go to Step 14 | -- |
13 | Replace the powertrain control module (PCM). Refer to Control Module References for replacement, setup, and programming. Is the action complete? | -- | Go to Step 14 | -- |
14 |
Does the DTC run and pass? | -- | Go to Step 15 | Go to Step 2 |
15 | With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? | -- | System OK | |
