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. This DTC sets if the engine control module (ECM) detects one of the following conditions:
| • | If the FTP sensor signal voltage is not within a calibrated range on a cold start-up. |
| • | If the FTP sensor signal does not change by a calibrated amount when purge is active. |
| • | If the FTP sensor signal oscillates more than a calibrated amount when vehicle speed is less than 30 km/h (50 mph). |
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 |
DTC Descriptor
This diagnostic procedure supports the following DTC:
DTC P0451 Fuel Tank Pressure (FTP) Sensor Performance
Conditions for Running the DTC
| • | The engine is operating for more than 3 seconds. |
| • | The fuel level is between 12-88 percent. |
| • | The start up engine coolant temperature (ECT) is less than 35°C (95°F). |
| • | The vehicle speed is between 10-31 km/h (6-19 mph). |
| • | The ECM is commanding purge. |
| • | The ratio between ambient pressure and the calculated manifold pressure is less than 0.6. |
| • | DTC P0451 runs continuously once the above conditions are met for more than 10 minutes. |
Conditions for Setting the DTC
| • | The ECM detects that the FTP on a cold start-up is less than -22.27 mm Hg (-11.93 in. H20) or more than 11.25 mm Hg (6.02 in. H20) for 25 seconds. |
| • | The ECM does not detect a change in tank vacuum when purge duty cycle is more than 40 percent. The change in vacuum must be less than 0.37 mm Hg (0.20 in. H2O) when purge is active. This condition requires 4 failures to set the DTC for 10 seconds each time. |
| • | The ECM detects that the FTP sensor signal oscillates more than 6.07 mm Hg (3.25 in. H20) from a zero point for more than 25 seconds. The zero point may vary and the vehicle speed must be less than 31 km/h (19 mph) for this test. |
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 MIL/DTC
| • | The malfunction indicator lamp (MIL) will turn OFF after 3 consecutive ignition cycles in which the diagnostic runs without a fault. |
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | Clear the DTCs with a scan tool. |
Diagnostic Aids
The following table illustrates the ECM connector locations:
ECM Connector Location | |
|---|---|
C2 | C1 |
Front of Vehicle | |
| • | Use the J 35616-A/BT-8637 Connector Test Adapter Kit for any test that requires probing the ECM harness connector or a component harness connector. |
| • | A blocked or clogged EVAP canister vent may set this DTC. |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step verifies that the condition is present.
-
The ECM produces a measurable steady state amperage that provides the 5-volt reference to the FTP sensor. If the amperage on the 5-volt reference circuit is less than 80 mA, test the 5-volt reference circuit for an open or high resistance.
-
This step tests the signal circuit of the FTP sensor.
-
This step tests for high resistance in the low reference circuit of the FTP sensor. The ECM must be completely powered down to obtain an accurate resistance reading. It may take up to 30 minutes for the ECM to power down after the ignition key is removed. Removal of the ECM fuse, or the PCM/ETC fuse, allows the ECM to power down completely.
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 - Vehicle? | -- | Go to Step 2 | |||||
Is the voltage within the specified range? | 1.0-2.5 V | Go to Step 3 | Go to Step 4 | |||||
3 |
Did the DTC fail this ignition? | -- | Go to Step 4 | Go to Diagnostic Aids | ||||
Is the amperage more than the specified value? | 80 mA | Go to Step 5 | Go to Step 7 | |||||
Is the voltage more than the specified value? | 4.8 V | Go to Step 6 | Go to Step 8 | |||||
Notice: Do NOT use a test lamp to test the continuity of the circuit. Damage to the control module may occur due to excessive current draw. Is the resistance less than the specified value? | 5 ohms | Go to Step 10 | Go to Step 9 | |||||
7 | Test the 5-volt reference circuit of the FTP sensor for high resistance between the harness connector and the control module. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 | ||||
8 | Test the signal circuit of the FTP sensor for high resistance between the harness connector and the control module. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 | ||||
9 | Test the low reference circuit of the FTP sensor for high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 12 | ||||
10 |
Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 11 | ||||
11 | Test for shorted terminals and for a poor connection at the FTP sensor harness connector, and the fuel tank harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 13 | ||||
12 | Test for shorted terminals and for a poor connection at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 15 | Go to Step 14 | ||||
13 | Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement . Did you complete the replacement? | -- | Go to Step 15 | -- | ||||
14 | Replace the ECM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 15 | -- | ||||
15 |
Did the DTC fail this ignition? | -- | Go to Step 2 | Go to Step 16 | ||||
16 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | -- | System OK | |||||
