Circuit Description
The powertrain control module (PCM) monitors the performance of the evaporative emission (EVAP) system by applying a predetermined level of vacuum to the EVAP system then monitors the vacuum decay rate. The PCM sets this DTC if the vacuum decay rate is more than a predetermined value.
Conditions for Running the DTC
| • | No active manifold absolute pressure (MAP) DTCs |
| • | No active intake air temperature (IAT) DTCs |
| • | No active throttle position (TP) DTCs |
| • | No active heated oxygen sensor (HO2S) DTCs |
| • | No active vehicle speed sensor (VSS) DTCs |
| • | No active system voltage DTCs |
| • | The ignition voltage is between 10-18 volts. |
| • | The barometric pressure is more than 75 kPa. |
| • | The fuel level is between 15-85 percent of full capacity. |
| • | The engine coolant temperature (ECT) is between 4°C (39°F) and 30°C (86°F). |
| • | The intake air temperature (IAT) is between 4°C (39°F) and 30°C (86°F). |
| • | The start up ECT and the IAT are within 9°C (16°F) of each other. |
Conditions for Setting the DTC
Important: This DTC does not report a first failed test. A first fail of this DTC will have a scan tool status as Not Run.
| • | The EVAP vacuum decay rate is more than a predetermined value. |
| • | The conditions are present for more than 2 seconds. |
OR
| • | The vacuum present in the EVAP system is more than a predetermined value. |
| • | The conditions are present for more than 4 seconds. |
Action Taken When the DTC Sets
| • | The PCM illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records. |
Conditions for Clearing the MIL/DTC
| • | The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A last test failed, or current DTC, clears when the diagnostic runs and does not fail. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Use a scan tool in order to clear the MIL and the DTC. |
Diagnostic Aids
Important:
• Remove any debris from the PCM connector surfaces before servicing
the PCM. Inspect the PCM connector gaskets when diagnosing or replacing
the PCM. Ensure that the gaskets are installed correctly. The
gaskets prevent water intrusion into the PCM. • An accurate indication of fuel level is required for the PCM to
properly pass or fail this DTC. Always diagnose fuel level sensor DTCs
before performing this DTCs diagnostic table. Always inspect
for fuel level sensor DTCs stored as History. • The Service Bay Test may have to be performed in cold ambient
air temperatures when the vehicle is running a winter grade fuel. The scan
tool displays a message when the Service Bay Test does not
run. • Inspect for charcoal release from the vapor canister. Refer to
the
Evaporative Emission System Cleaning
procedure.
Conditions for Running the Service Bay Test
| • | The battery voltage is between 10.5-17.5 volts. |
| • | The fuel level is between 15- 85 percent of the full capacity. |
| • | The engine temperature is between 3.5°C (38°F) and 35°C (95°F). |
Perform a physical inspection of the EVAP system. Inspect for the following conditions:
| • | A loose, missing, defective, or incorrect fuel tank cap |
| • | Incorrectly routed or defective EVAP system vacuum and vapor lines |
| • | A malfunctioning or damaged vapor canister |
| • | Charcoal release from the vapor canister--Refer to Evaporative Emission System Cleaning . |
The vacuum and pressure in the EVAP system is measured in inches of water (H2O). Most gauges measure vacuum in inches of mercury (Hg) and pressure in pounds per square inch (psi). The following shows how the values compare:
in H2O | in Hg | psi |
|---|---|---|
1in H2O | 0.07 in Hg | 0.0361 psi |
5 in H2O | 0.36 in Hg | 0.180 psi |
10 in H2O | 0.73 in Hg | 0.361 psi |
15 in H2O | 1.10 in Hg | 0.541 psi |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
Tests the fuel tank pressure.
-
An intermittent leak or restriction is indicated if the vehicle passes the Service Bay Test. A fuel tank cap that is loose or off causes this DTC to set.
If the Service Bay Test cannot be run, proceed to step 5. If a fault is not currently present, the diagnostic table steps will return you to Step 3.
-
Tests the vapor canister and the EVAP vent valve for restriction.
-
A fuel tank pressure sensor that does not correctly respond to pressure, or vacuum, causes this DTC to set.
Step
| Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | ||||||
Important: An open in the fuel tank pressure sensor ground circuit causes the voltage to go high. An open ground circuit may cause DTC P0446 to set, because the PCM senses a fuel tank pressure sensor voltage that is stuck in range, which indicates a restricted EVAP system. An intermittent leak or restriction is indicated if the vehicle passes the Service Bay Test. If the Service Bay Test cannot be run, proceed to step 5. If a fault is not currently present, the diagnostic table steps will return you to Step 3.Is the fuel tank pressure near the specified value? | 0 in. Hg | Go to DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage | ||||||
3 |
Did you find and correct the condition? | -- | ||||||
|
Important: Ensure that the Conditions for Running the Service Bay Test are met before proceeding with this diagnostic. Refer to Diagnostic Aids. Perform the EVAP system Service Bay Test. Does the vehicle pass the Service Bay Test? | -- | Go to Diagnostic Aids | ||||||
|
Important: The DTCs must be cleared from the PCM in order to use the output control function on the scan tool.
Important: If an audible solenoid click cannot be heard and DTC P0449 is not set, inspect the EVAP canister vent solenoid circuits for high resistance. Does the vacuum drop from the specified value when the EVAP vent valve is opened? | 5 in. Hg | |||||||
6 |
Does the vacuum drop from the specified value when the vent line is unplugged? | 5 in. Hg | ||||||
7 |
Did you find and correct the condition? | -- | ||||||
8 |
Did you find and correct the condition? | -- | ||||||
Important: Always zero the EVAP pressure and vacuum (in H2O) gauges on the EVAP pressure and purge diagnostic station before proceeding with diagnosis. Important: The fuel tank pressure sensor range is from +7.5 in. H2O of pressure to -17.5 in. H2O of pressure or vacuum. In order to test the fuel tank pressure sensor for vacuum response, command the EVAP purge solenoid valve ON with the engine running and quickly SEAL the system using the scan tool. Leaving the EVAP purge solenoid valve ON for a longer period of time allows a greater level of vacuum to develop. Does the fuel tank pressure sensor indicate the actual amount of pressure in the EVAP system? | -- | |||||||
10 | Replace the EVAP vent valve. Refer to Evaporative Emission Vent Valve Replacement . Is the action complete? | -- | -- | |||||
11 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Is the action complete? | -- | -- | |||||
12 | Replace the fuel tank pressure sensor. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | -- | |||||
13 |
Does the scan tool indicate that this test ran and passed? | -- | ||||||
14 | Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK |
