Circuit Description
The evaporative system includes the following components:
| • | The fuel tank |
| • | The EVAP vent solenoid |
| • | The fuel tank pressure sensor |
| • | The fuel pipes and hoses |
| • | The vapor lines |
| • | The fuel cap |
| • | The evaporative emission canister |
| • | The purge lines |
| • | The EVAP purge solenoid |
The EVAP purge solenoid valve allows the manifold vacuum to purge the canister. The Vehicle Control Module (VCM) supplies a ground in order to energize the solenoid valve (purge ON). The EVAP purge solenoid control by the VCM is Pulse Width Modulated (PWM) or turned ON and OFF several times a second. The duty cycle (pulse width) is determined by the engine operating conditions including the load, the throttle position, the coolant temperature, and the ambient temperature. The duty cycle is calculated by the VCM, and the purge solenoid is commanded ON when certain conditions have been met.
The system checks for conditions that cause the EVAP system to purge continuously by commanding the EVAP vent solenoid ON and the EVAP purge solenoid OFF (EVAP vent solenoid CLOSED, EVAP purge PWM 0%). If the fuel tank pressure level increases during the test, a continuous purge flow condition is indicated. The following items can cause this condition:
| • | A leaking EVAP purge solenoid |
| • | A grounded EVAP purge solenoid driver circuit |
If any of these conditions are present, a DTC P1441 sets. This DTC is a type B DTC.
Conditions for Setting the DTC
| • | There are no MAP sensor DTCs |
| • | There are no TP sensor DTCs |
| • | There are no VSS DTCs |
| • | There are no HO2S DTCs |
| • | There are no ECT DTCs |
| • | The DTC P0125 is not active |
| • | There are no IAT sensor DTCs |
| • | The Fuel Tank Level is greater than 12.5% and 87.5% |
| • | The System Voltage is greater than 10 volts but less than 17 volts |
Cold Start Test
| • | The ECT is greater than 3.75°C (38.75°F) but less than 30°C (86°F). |
| • | The IAT is greater than 3.75°C (38.75°F) but less than 30°C (86°F). |
| • | The change in temperature between the ECT and the IAT is less than 1.5°C if the IAT is greater than the ECT. |
| • | The change in temperature between the ECT and the IAT is less than 8.25°C if the ECT is greater than the IAT. |
| • | The Baro is greater than 75 kPa. |
Excess Vacuum Test
| • | The vent solenoid is commanded open. |
| • | The fuel tank vacuum is less than 7 inches H2O. |
Weak Vacuum Test
| • | The TP sensor is at least 5%. |
| • | The speed is less than 65 mph. |
| • | The fuel tank vacuum is at least 9 inches H20 within 12.5 seconds. |
Purge Valve Leak Test
| • | The purge valve is closed. |
| • | The TP sensor is greater than 0% but less than 99.6%. |
| • | The vacuum is at least 5 kPa. |
| • | The fuel tank vacuum is at least 12 inches H2O within 37.5 seconds after a 15 second delay. |
Action Taken When the DTC Sets
| • | The VCM turns the MIL (Malfunction Indicator Lamp) ON 2 consecutive failures. |
| • | The VCM records the operating conditions at the time the diagnostic fails. The Freeze Frame and Failure Records store this information. |
Conditions for Clearing the MIL/DTC
The following conditions will clear the DTC:
| • | The VCM turns the MIL OFF on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present |
| • | A history DTC clears after 40 consecutive warm-up cycles have occurred without a fault |
| • | The scan tool Clear Info function or disconnecting the VCM battery feed can clear the DTC |
Diagnostic Aids
Check for the following conditions:
| • | Inspect the EVAP lines for charcoal contamination if the EVAP Purge Solenoid was replaced. If charcoal contamination is present, replace the EVAP canister. Clean the EVAP purge line in order to remove any additional charcoal. |
| • | Inspect the VCM for a poor connection. Inspect the harness connectors for the following items: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wiring connections |
| • | Inspect the wiring harness for damage. If the harness looks OK, connect the Enhanced EVAP Pressure Purge Diagnostic Cart to the EVAP service port. Pressurize the EVAP system to 10 inch H2O. Observe the Fuel Tank Pressure display on the scan tool while moving the connectors and wiring harnesses related to the EVAP purge solenoid. A sudden change in the display indicates the location of the fault. |
Refer to Carbon Particle Removal from EVAP System before starting repairs.
Reviewing the Fail Records vehicle mileage since the Diagnostic Test Last Failed may help to determine how often the condition that caused the DTC to set occurs. This may assist in diagnosing the condition.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
-
This step checks the fuel tank pressure sensor at ambient pressure. The fuel tank pressure sensor is zeroed at every key on in order to compensate for changes in the atmospheric pressure.
-
This step checks for a stuck open EVAP purge solenoid.
-
This step verifies that the fuel tank pressure sensor accurately reacts to the EVAP system pressure changes.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing the DTCs, use the scan tool in order to record the Freeze Frame and Failure Records for reference. This data will be lost when the Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Is the Fuel Tank Pressure at the specified value? | 0 in H2O ±1 in. H2O | |||
|
Important: Before continuing with the diagnosis, zero the EVAP Pressure and Vacuum gauges on the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413. Refer to tool operating instructions.
Is the Fuel Tank Pressure at the specified value? | 5 in H2O | |||
Is the Fuel Tank Pressure at the specified value? | 5 in H2O 5 in H2O (±1 in H2O) | |||
5 |
Does the EVAP purge solenoid maintain the vacuum? | 15 in Hg | ||
6 |
Was a problem found? | -- | Go to Diagnostic Aids | |
7 | Replace the EVAP purge solenoid. Refer to Diagnostic Aids. Refer to EVAP Canister Purge Solenoid . Is the action complete? | -- |
Go to Diagnostic Aids | -- |
8 | Repair as necessary. Refer to Diagnostic Aids. Is the action complete? | -- | -- | |
9 |
Does the Fuel Tank Pressure remain at the specified value while the seal system function is being used? | 2500 RPM 0 in H2O | System OK |
