Circuit Description
The evaporative system includes the following components:
| • | The EVAP canister vent valve. |
| • | The fuel tank pressure sensor. |
| • | The fuel pipes and hoses. |
| • | The evaporative emission canister. |
The Powertrain Control Module (PCM) supplies a ground to energize the
valve valve (purge ON). The EVAP purge valve control is Pulse Width Modulated
(PWM) or turned ON and OFF several times a second. The duty cycle (pulse width)
is determined by engine operating conditions including load, throttle position,
coolant temperature and ambient temperature. The duty cycle is calculated
by the PCM and the output is commanded when the appropriate conditions have
been met. The system checks for conditions that cause the EVAP system to purge
continuously by commanding the EVAP canister vent valve ON and the EVAP purge
valve OFF (EVAP canister vent valve CLOSED, EVAP purge PWM 0%). If vacuum
level in the fuel tank increases during the test, a continuous purge flow
condition is indicated. This can be caused by any of the following conditions:
| • | EVAP purge valve leaking. |
| • | EVAP purge and engine vacuum lines switched at the EVAP purge
valve. |
| • | EVAP purge valve control circuit grounded. |
If any of these conditions are present, DTC P1441 will set.
Conditions for Setting the DTC
| • | No TP sensor, ODM, IAT sensor, or MAP sensor DTCs set. |
| • | The DTC P0442 diagnostic test has passed. |
| • | A continuous open purge flow condition is detected during the
diagnostic test (fuel tank pressure decreases to less than -11 in. H2O). |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during
the first trip in which the diagnostic test has been run and failed. |
| • | The PCM will store conditions which were present when the DTC
set as Freeze Frame and Failure Records data. |
Important: Although these diagnostics are considered type A, they act like type
B diagnostics under certain conditions. Whenever the EVAP diagnostics report
that the system has passed, or if the battery has been disconnected, the diagnostic
must fail during two consecutive cold start trips before setting a DTC. The
initial failure is not reported to the diagnostic executive or displayed on
a scan tool. A passing system always reports to the diagnostic executive immediately.
Conditions for Clearing the MIL/DTC
| • | The PCM will turn OFF the MIL during the third consecutive trip
in which the diagnostic has been run and passed. |
| • | The History DTC will clear after 40 consecutive warm-up
cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using the scan tool. |
Diagnostic Aids
Check for the following conditions:
| • | Poor connection at the PCM. |
| | Inspect harness connectors for backed out terminals, improper mating,
broken locks, improperly formed or damaged terminals, and poor terminal to
wire connection. |
| | Inspect the wiring harness for damage. |
| • | If the harness appears to be OK, connect the
|
| • | Incorrect vacuum line routing. |
| | Verify that the source vacuum line routing to the EVAP purge valve is
correct and that the EVAP purge and source vacuum lines to the EVAP purge
valve are not switched. |
| • | Malfunctioning or damaged canister. |
| | A malfunctioning canister may intermittenly allow charcoal into the
EVAP purge valve, EVAP vent solenoid and associated lines causing a DTC to
be set. Use the following procedure to check for a carbon release condition: |
| 1. | Turn OFF the ignition switch. |
| 3. | Lightly tap the EVAP purge valve and (if applicable) the vacuum
switch on a clean work area looking for carbon particles exiting either of
the vacuum ports. |
| 4. | If no carbon release is evident, reinstall the components and
continue with the DTC P1441 table. If carbon is being released from either
component, continue with this service procedure. |
| 5. | Remove the EVAP canister from the vehicle. |
| 6. | Ensure that the main cylinder valve is turned off on the
|
| 7. | Disconnect the black hose that connects the nitrogen cylinder
to the EVAP purge/pressure diagnostic station at the pressure regulator by
unscrewing the knurled nut on the regulator. No tools are required to remove
the black hose from the regulator. |
| 8. | Using a section of vacuum line, connect one end over the open
threaded fitting of the EVAP purge/pressure diagnostic station pressure regulator. |
| 9. | Connect the remaining end to the EVAP purge valve end of the EVAP
purge line at the vehicle and turn on the main nitrogen cylinder valve. Continue
to blow any debris from the purge line for 15 seconds. |
| 10. | Return the EVAP Pressure/Purge Diagnostic Station to its original
condition by re-installing the black hose that was disconnected in step 7. |
| 11. | Replace the following components: |
| 12. | Proceed with the the DTC P1441 diagnostic table. |
Reviewing the Fail Records vehicle mileage since the diagnostic test
last failed may help determine how often the condition that caused the DTC
to set occurs. This may assist in diagnosing the condition.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
-
The PCM will command the EVAP purge and EVAP canister vent valves closed
with the scan tool Seal System EVAP output control function activated. Fuel
tank pressure should not decrease under this condition.
-
The PCM commands
the EVAP purge valve OFF (open) and the EVAP canister vent valve ON (closed)
with the scan tool System Perf. EVAP output control function activated. Engine
vacuum should cause fuel tank pressure to decrease when System Perf. is activated.
Enhanced Evaporative Emission System Check
Step
| Action
| Value(s)
| Yes
| No
|
1
| Was
the Powertrain On-Board Diagnostic (OBD) System Check performed?
| --
|
Go to Step 2
| Go to the
Powertrain On Board Diagnostic (OBD) System Check
|
2
|
Important: Visually/physically inspect for the following conditions:
| • | Loose or missing fuel cap. |
- Turn OFF the ignition switch.
- Remove the fuel cap.
- Turn ON the ignition switch.
- Observe Fuel Tank Pressure on the scan tool.
Is Fuel Tank Pressure at the specified value?
| 0 in. H2O
|
Go to Step 3
| Go to
Fuel Tank Pressure Sensor Diagnosis
|
3
|
Important:: Before continuing with diagnosis, zero the EVAP Pressure and Vacuum
(inches of H2O) gauges on the
- Replace the fuel cap.
- Using the scan tool, command the EVAP canister vent valve ON (Closed).
- Connect the EVAP pressure/purge diagnostic station to the EVAP
service port.
- Pressurize the EVAP system to the specified value using the
- Observe Fuel Tank Pressure on the scan tool.
Is Fuel Tank Pressure at the specified value?
| 5 in. H2O
|
Go to Step 4
| Go to
Fuel Tank Pressure Sensor Diagnosis
|
4
| Monitor the EVAP Pressure gauge on the EVAP pressure/purge
diagnostic station while commanding the EVAP canister vent valve OFF (Open).
Does EVAP Pressure decrease to the specified value within 5 seconds?
| 0 in. H2O
|
Go to Step
5
| Go to
DTC P0446 Evaporative Emission (EVAP) Vent System Performance
|
5
|
- Start the engine.
- Remove the fuel cap.
- Using the scan tool output tests function, select Seal System
and activate.
- Replace the fuel cap.
- Switch the rotary switch on the EVAP pressure/purge diagnostic
station to PURGE.
- Run the engine at idle while monitoring the Vacuum (inches of
H2O) gauge on the EVAP pressure/purge diagnostic station.
Is vacuum increasing to a value greater than the specified value?
| 0 in. H2O
| Go to
DTC P1441 Evaporative Emission (EVAP) System Flow During Non-Purge
|
Go to Step
6
|
6
|
- Using the scan tool output tests function, select System Perf.
and activate.
- Switch the rotary switch on the EVAP pressure/purge diagnostic
station to PURGE.
- Run the engine at 2500 RPM while monitoring the Vacuum (in. of
H2O) gauge on the EVAP pressure/purge diagnostic station for at least 10 seconds.
Did vacuum increase to a value greater than the specified value?
| -5 in H2O
| System OK
| Go to
DTC P0440 Evaporative Emission (EVAP) System
|
