Circuit Description
The control module monitors the fuel tank pressure (FTP) sensor signal in order to detect vacuum decay and excess vacuum during the evaporative emission (EVAP) diagnostic test. The control module supplies a 5-volt reference and a low reference circuit to the FTP sensor. If the FTP sensor signal voltage is not within a calibrated value range during a cold engine start, this DTC sets.
The following table illustrates the relationship between FTP sensor signal voltage and the EVAP system pressure/vacuum.
FTP Sensor Signal Voltage | Fuel Tank Pressure |
|---|---|
High, Approximately 1.5 Volts or More | Negative Pressure/Vacuum |
Low, Approximately 1.5 Volts or Less | Positive Pressure |
Conditions for Running the DTC
| • | DTCs P0452 and P0453 are not set. |
| • | The start up ECT is less than 35°C (95°F). |
| • | The engine run time is between 1 and 2 seconds. |
| • | The engine is idling. |
| • | The EVAP diagnostics are not running. |
| • | DTC P0451 diagnostic runs once per ignition cycle. |
Conditions for Setting the DTC
| • | The FTP voltage is less than 0.78 volts or greater than 2.94 volts. |
| • | The condition is present for more than 10 seconds. |
Action Taken When the DTC Sets
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the DTC
| • | A current DTC Last Test Failed clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other non-emission related diagnostic. |
| • | Clear the DTC with a scan tool. |
Diagnostic Aids
| Important: Inaccurate readings will occur if resistance measurements are taken on a fuel tank pressure sensor. The fuel tank pressure sensor contains an internal amplifier circuit that requires applied voltage to function properly. |
| • | The FTP sensor on the scan tool should read between 1.30-1.70 volts with the ignition ON and the engine OFF and the fuel cap removed. This represents atmospheric pressure, or 0 inches of vacuum. |
| • | DTC P0451 indicates that the fuel tank pressure sensor signal voltage is skewed. Possible causes of DTC P0451 are as follows: |
| - | Corrosion in the fuel tank inline harness connector |
| - | Corrosion in the engine I/P inline harness connector |
| - | Corrosion in the fuel tank pressure sensor harness connector |
| - | The fuel tank pressure sensor skewed |
| • | For intermittent conditions, refer to Intermittent Conditions . |
Step | Action | Values | Yes | No |
|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views | ||||
1 | Did you perform the Diagnostic System Check-Engine Controls? | -- | Go to Step 2 | |
2 | Monitor the fuel tank pressure (FTP) sensor voltage with the scan tool, with the fuel cap removed. Is the FTP sensor value within the specified range? | 1.0-2.85 V | Go to Step 3 | Go to Step 4 |
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids |
4 |
Is the voltage near the specified value? | 5 V | Go to Step 5 | Go to Step 6 |
5 | Measure the voltage from the 5-volt reference circuit to the low reference circuit at the fuel tank harness connector, the control module side, with a DMM. Is the voltage near the specified value? | 5 V | Go to Step 8 | Go to Step 7 |
6 | Test the 5-volt reference circuit of the FTP sensor for an open or short to ground between the harness connector and the control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 |
7 | Test the low reference circuit of the FTP sensor for an open or for high resistance between the harness connector and the control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 10 |
8 |
Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 9 |
9 | Inspect for poor connections at the FTP sensor harness connector and the fuel tank harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 11 |
10 | Inspect for poor connections at the harness connector of the control module. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 13 | Go to Step 12 |
11 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
12 | Replace the control module. Refer to Engine Control Module Replacement . Did you complete the replacement? | -- | Go to Step 13 | -- |
13 |
Did the DTC fail this ignition | -- | Go to Step 2 | Go to Step 14 |
14 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |
