Circuit Description
The EVAP purge valve allows manifold vacuum to purge the canister. The Powertrain Control Module (PCM) supplies a ground to energize the EVAP purge 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:
| • | Engine coolant temperature above 25°C (77°F). |
| • | After the engine has been running about 2 1/2 minutes on a cold start or 30 seconds on a warm start. |
| • | The vehicle is operating in closed loop fuel control. |
Canister purge commanded duty cycle varies according to operating conditions determined by mass air flow, fuel trim, and. intake air temperature.
Canister purge operation is also affected by throttle position.
| • | VIN 1 -- Canister purge will be disabled if TP angle increases to above 33%. Canister purge will be re-enabled when TP angle decreases below 29%. |
| • | VIN K -- Canister purge will be disabled if TP angle increases to above 70%. Canister purge will be re-enabled when TP angle decreases below 66%. |
The EVAP vacuum switch is a normally closed switch positioned in the purge line between the canister and the EVAP purge valve. The EVAP vacuum switch will open when vacuum increases to greater than 5 inches of water in the purge line. The PCM monitors the EVAP purge vacuum switch signal to determine of the evaporative emission control system is working properly. If the switch is closed (no purge flow) when the PCM is commanding the EVAP purge valve ON, DTC P0441 will be set.
Conditions for Setting the DTC
| • | No TP sensor, IAT sensor, MAP sensor, ECT sensor, or MAF sensor DTCs set. |
| • | BARO reading is greater than 70 kPa. |
| • | Engine Coolant Temperature is less than 114°C (237°F). |
| • | Intake Air Temperature (IAT) sensor indicates an ambient temperature between 10°C (50°F) and 70°C (158°F). |
| • | The difference between ECT and IAT is less than 10°C (18°F). |
| • | Engine speed is between 900 rpm and 5000 rpm. |
| • | Throttle angle is between 2.5% and 40%. |
| • | Canister purge PWM is greater than 85%. |
| • | EVAP vacuum switch remains closed (12 volts signal at the PCM). |
| • | Above conditions for longer than 4 seconds. |
Action Taken When the DTC Sets
| • | The PCM will illuminate the malfunction indicator lamp (MIL) during the second consecutive 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. |
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 PCM. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection. |
| • | Damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the EVAP vacuum switch display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault. |
| • | Faulty or damaged canister. A faulty canister may intermittently allow charcoal into the EVAP purge solenoid, EVAP vacuum switch, and associated lines, causing a DTC to be set. |
Reviewing the Fail Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||||||
2 |
Does the EVAP Vacuum Sw. display Purge with the EVAP purge solenoid commanded ON? | -- | ||||||
3 |
Note test result; does scan tool indicate DTC P0441 failed this ign? | -- | Refer to Diagnostic Aids | |||||
4 |
Does the scan tool display Purge? | -- | ||||||
5 | Check the vacuum line to canister for damage or improper connections. Was a problem found? | -- | ||||||
6 |
Does the gauge indicate vacuum greater than the specified value? | 12 in. Hg | ||||||
7 |
Does the scan tool display Purge? | -- | ||||||
8 |
Does the gauge indicate vacuum greater than the specified value? | 12 in. Hg | ||||||
9 |
Was a problem found? | -- | ||||||
10 |
Is the test light ON? | -- | ||||||
11 |
Is the test light ON? | -- | ||||||
12 | Check for a poor connection at the PCM. Was a problem found? | -- | ||||||
13 |
Is action complete? | -- | -- | |||||
14 | Replace the EVAP canister. Go to Evaporative Emission Canister Replacement . Is action complete? | -- | -- | |||||
15 | Replace the EVAP vacuum switch. Go to Evaporative Emission Vacuum Switch Is action complete? | -- | -- | |||||
16 | Locate and repair the cause of no vacuum. Is action complete? | -- | -- | |||||
17 |
Was a problem found? | -- | ||||||
18 | Replace the EVAP purge solenoid. Go to Evaporative Emission Canister Purge Solenoid Is action complete? | -- | -- | |||||
Replace the PCM. Important:: The replacement PCM must be programmed. Go to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||||||
20 |
Note test result; does the scan tool indicate DTC P0441 failed this ign? | -- | System OK |
