Circuit Description
The evaporative emission (EVAP) system is tested by applying vacuum to the EVAP system and monitoring for a vacuum decay. The PCM monitors the vacuum level through the fuel tank vapor pressure sensor signal. At an appropriate time, the EVAP canister purge valve and the EVAP vent solenoid are turned on, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge valve is turned off, sealing the system. A leak is detected by monitoring for a decrease in vacuum level over a given time period, when all other variables remain constant. A leak, blockage or poor component in the system will cause a DTC to set.
Diagnosis
| • | The EVAP canister purge valve operation is covered in this section and diagnosed in DTCs P0440, P0446, and P1441. |
| • | The EVAP vent valve operation is covered in this section and diagnosed in DTCs P0440, P0442, and P0446. |
| • | The fuel tank vapor pressure sensor operation is covered in this section and diagnosed in DTCs P0440, P0442, P0446, P0452, P0453, P1441 and in the Evaporative Emission System Check. |
| • | A open or a shorted circuit in the EVAP canister purge valve and EVAP vent valve can also be diagnosed in Powertrain Control Module Outputs Diagnosis . |
Visual Check of the EVAP Canister
If the canister is cracked or damaged, replace the canister. Refer to Evaporative Emission Canister Replacement .
Diagnostic Aids
Inspect for the following conditions:
| • | Poor connection at PCM. Inspect harness connectors for the following conditions: |
| - | Backed out terminals |
| - | incorrect mating |
| - | Broken locks |
| - | incorrectly formed |
| - | Damaged terminals |
| - | Poor terminal to wire connection |
| • | A damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Vacuum Pressure on a scan tool while moving the electrical connectors and the wiring harnesses related to the sensor. A change in the display will indicate the location of the malfunction. |
| • | An incorrect purge or vacuum source line routing. Verify that the source vacuum and purge lines to the EVAP canister purge valve are not switched. |
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On-board Diagnostic (OBD) System Check? | -- | Go to Step 2 | |
2 | Use a scan tool in order to command the EVAP canister purge valve and the vent solenoid on and off. Do the purge valve and the vent solenoid click when commanded on and off? | -- | Go to Step 3 | |
3 |
Does the pressure equal the specified value? | -0.32 - +0.32 kPa (-1.28 - +1.28 in. H2O) | Go to Step 4 | Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage or DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage |
4 |
Important:: Before continuing with diagnosis, zero the EVAP Pressure and Vacuum gauges on the J 41413 EVAP pressure/purge diagnostic station. Refer to the tool operating instructions.
Important: Do not exceed the pressure given in the first specified value. Does the pressure equal the second specified value? | 1.25 kPa (5 in. H2O) .96 kPa (3.85 in. H2O) | Go to Step 5 | Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage or DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage |
5 | Use a scan tool in order to commanded the vent solenoid off while observing the EVAP system pressure on the diagnostic station. Does the pressure decrease to the specified value within 5 seconds? | 0 kPa (0 in. H2O) | Go to Step 6 | Go to DTC P0446 Evaporative Emission (EVAP) Vent System Performance |
6 |
Does the pressure decrease? | -- | Go to DTC P1441 Evaporative Emission (EVAP) System Flow During Non-Purge | Go to Step 7 |
7 |
Does the pressure decrease? | -- | System OK |
