Circuit Description
The EVAP control system leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring vacuum decay. The powertrain control module (PCM) monitors the vacuum level via the fuel tank pressure sensor input. The PCM turns ON the EVAP canister purge valve and the EVAP vent solenoid, allowing engine manifold pressure (vacuum) to draw a small vacuum on the entire evaporative emission system. If a sufficient vacuum cannot be sustained over a given period of time, a small leak (or a malfunction) is suspected and a DTC P0440 sets.
The evaporative emission (EVAP) system as defined by federal regulation includes the following components:
| • | Fuel tank |
| • | EVAP vent solenoid |
| • | Fuel tank pressure sensor |
| • | Fuel pipes and hoses |
| • | Vapor lines |
| • | Fuel filler cap |
| • | Fuel tank pressure control valve |
| • | Evaporative emission canister |
| • | Purge lines |
| • | EVAP canister purge valve |
Conditions for Running the DTC
| • | The ignition is ON |
| • | The engine is running |
| • | The engine is operating in closed loop |
Conditions for Setting the DTC
Fuel tank pressure change:
| • | Engine coolant temperature is between 70°C (158°F) and 110°C (230°F). |
| • | Intake air temperature is between -7°C (19°F) and 70°C (158°F). |
| • | Barometric pressure is more than 75 kPa. |
| • | Engine speed is between 1,000 and 3,000 RPM (A/T), 1,000 and 3,500 RPM (M/T). |
| • | Fuel tank level is less than 75 percent. |
| • | Purge accumulation time is more than 360 seconds. |
Diagnostic may take up to 20 minutes to run.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL will turn OFF after three consecutive drive cycles without a fault present. |
| • | A DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed. |
Diagnostic Aids
A DTC P0440 is more likely to set during city driving. Avoid operating the vehicle for long periods on the highway when validating a DTC P0440.
The EVAP purge diagnostic checks for many of the faults that can cause a DTC P0440 to set. If the EVAP purge test passes the cause of the DTC P0440 is probably intermittent. Clear the DTCs. Road test the vehicle while monitoring the EVAP purge test in the MIL/System Status selection under System Information on the scan tool. When the EVAP purge test indicates complete with a YES status, check for a DTC P0440 under Last Test Failed. If there is no DTC P0440 indicated, the DTC is intermittent and the purge system diagnostic is indicating OK at this time.
Check for any of the following conditions:
| • | Cracked or punctured EVAP canister |
| • | A damaged or disconnected source vacuum line, EVAP purge line, vent hose or fuel tank vapor line |
| • | A faulty or erratic fuel level sensor can cause a DTC P0440 to set |
| • | A faulty or erratic fuel tank pressure sensor can cause a DTC P0440 to set |
| • | A faulty EVAP canister purge valve |
| • | A faulty EVAP canister vent solenoid |
| • | A faulty EVAP tank pressure control solenoid vacuum valve |
For functional checks of the components listed above, refer to Evaporative Emission Control System Diagnosis .
An intermittent malfunction may be caused by a fault in any of the EVAP control system electrical circuits. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals |
| • | Improper mating of terminals |
| • | Broken electrical connector locks |
| • | Improperly formed or damaged terminals |
| • | Faulty terminal to wire connections |
| • | Physical damage to the wiring harness |
| • | A broken wire inside the insulation |
| • | Corrosion of electrical connections, splices, or terminals |
If the DTC P0440 is intermittent, driving the vehicle under the following conditions can verify whether the fault is present. Perform the scan tool Clear DTC Information function. Road test the vehicle while monitoring the DTC P0440 diagnostic on the scan tool under the Not Ran Since Code Cleared selection in the DTC Information menu. If a DTC P0440 appears in the Not Ran Since Code Cleared list, the P0440 diagnostic has not yet run. When the DTC P0440 does not appear in the Not Ran Since Code Cleared list, the P0440 diagnostic has run. If the MIL is NOT ILLUMINATED, and there is no PENDING DTC Status in DTC Information, the P0440 diagnostic has passed. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the Not Ran Since Code Cleared list. DO NOT FORGET that the Not Ran Since Code Cleared list only indicates that the test has run, not whether the test passed or failed. The DTC Information screen must be checked for CURRENT or PENDING status, in order to determine the outcome of the diagnostic test involved.
If you duplicate the DTC P0440, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Powertrain OBD System Check prompts the technician to complete some basic checks and to store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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If any other EVAP DTCs except a DTC P0455 are set, diagnose those DTCs first.
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This step checks the operation of the EVAP tank pressure control solenoid valve. The EVAP tank pressure control solenoid valve output control is disabled by the PCM when any DTCs are stored and when engine speed is indicated.
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This step checks the EVAP tank pressure control solenoid valve control circuit. A short to ground will keep the EVAP tank pressure control solenoid vacuum valve open and cause the system to fail. The EVAP tank pressure control solenoid valve output control is disabled by the PCM when any DTCs are stored and when engine speed is indicated.
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This step checks the components that supply manifold vacuum to the EVAP canister purge valve.
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This step checks the operation of the EVAP canister purge valve. The EVAP canister purge valve duty cycle control is disabled by the PCM when any DTCs are stored and when engine speed is indicated.
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This step checks the operation of the EVAP canister vent solenoid. The EVAP canister vent solenoid output control is disabled by the PCM when any DTCs are stored and when engine speed is indicated.
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This step checks the EVAP canister vent solenoid control circuit. The EVAP canister vent solenoid output control is disabled by the PCM when any DTCs are stored and when engine speed is indicated.
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This step uses tools from the EVAP Pressure/Purge Cart Diagnostic Station, in order to determine whether EVAP control system is sealed sufficiently to be pressurized. Any leak that is found must be located and repaired before continuing with the diagnosis.
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Use the ultrasonic leak detector in order to locate any leaks after pressurizing the EVAP system.
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This step checks the EVAP canister for blockage or restrictions.
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The DTC P0440 diagnostic can be monitored on the scan tool under the MIL/System Status selection of System Information. When the EVAP purge test displays a YES status (indicating that the purge system diagnostic is completed) check for a DTC P0440 in the Last Test Failed screen of the scan tool. If there is no DTC P0440 displayed the EVAP purge system diagnostic has run and passed, indicating that no malfunction was present this time. DTCs MUST BE CLEARED in order to view the CURRENT STATUS of the system diagnostics being performed. Do not forget that the MIL/System Status tests only indicate that the test has run, not whether the test passed or failed. The Last Test Failed screen must be checked for related DTCs in order to determine the outcome of the diagnostic test involved.
Step | Action | Value(s) | Yes | No | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||||||||||
Are any other EVAP codes set with the exception of the P0455? | -- | |||||||||||||||
3 | Visually inspect the entire EVAP control system for any of the following conditions:
Was a problem found? | -- | ||||||||||||||
4 |
Caution: Do not breathe the air through the EVAP component tubes or hoses. The fuel vapors inside the EVAP components may cause personal injury.
Important: There will be some resistance, but air should flow steadily. Did the air flow through the valve to the tank port side? | -- | ||||||||||||||
5 |
Important: The fuel tank pressure control valve will not allow air to flow from the tank side port to the canister side port until the pressure on the tank port side is more than 3.5 kPa (0.5 psi).
Did the fuel tank pressure control valve pass both checks? | 51 kPa (15 in Hg) | ||||||||||||||
Did the air pass through the valve and out the manifold vacuum side? | -- | |||||||||||||||
7 |
Was a repair necessary? | -- | ||||||||||||||
8 |
Did the test lamp illuminate? | -- | ||||||||||||||
Does the test lamp indicate that the EVAP tank pressure control solenoid valve control circuit passed both checks? | -- | |||||||||||||||
Was a repair necessary? | -- | |||||||||||||||
Did the EVAP canister purge valve pass both inspections? | -- | |||||||||||||||
12 |
Did the test lamp illuminate? | -- | ||||||||||||||
13 |
Did the test lamp flash and then illuminate fully as the duty cycle reached 100 percent? | -- | ||||||||||||||
14 |
Does the solenoid hold vacuum? | 51 kPa (15 in Hg) | ||||||||||||||
Does the solenoid hold vacuum? | 51 kPa (15 in Hg) | |||||||||||||||
16 | While the EVAP canister vent solenoid is still holding vacuum from step 15, use the scan tool to command the EVAP canister vent solenoid OFF. Did the vacuum drop to the specified value? | 0 kPa (0 in Hg) | ||||||||||||||
17 |
Did the test lamp illuminate? | -- | ||||||||||||||
Did the test lamp illuminate? | -- | |||||||||||||||
Does the pressure decrease to less than the second specified value within 2 minutes? | 28 mm Hg (15 in Hg) 18.6 mm Hg (10 in Hg) | |||||||||||||||
Did you find any leaks? | 56 mm Hg (30 in Hg) | |||||||||||||||
21 | Replace any leaking or faulty EVAP control system components. Is the action complete? | -- | -- | |||||||||||||
Did the vacuum gauge read any pressure? | 18.6 mm Hg (10 in Hg) | Go to Diagnostic Aids | ||||||||||||||
23 | Repair the open in the ignition positive voltage circuit between terminal 1 and the main relay. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||||||||||
24 |
Was a repair necessary? | -- | ||||||||||||||
25 | Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement . Is the action complete? | -- | -- | |||||||||||||
26 |
Was a repair necessary? | -- | ||||||||||||||
27 |
Was a repair necessary? | -- | ||||||||||||||
28 | Replace the EVAP canister vent solenoid. Refer to Evaporative Emission Canister Vent Solenoid Replacement . Is the action complete? | -- | -- | |||||||||||||
29 | Replace the fuel tank pressure control valve. Refer to Fuel Tank Pressure Control Valve Replacement . Is the action complete? | -- | -- | |||||||||||||
30 |
Was a repair necessary? | -- | ||||||||||||||
31 | Replace the EVAP canister purge valve. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement . Is the action complete? | -- | -- | |||||||||||||
32 |
Was a repair necessary? | -- | ||||||||||||||
33 | Replace the EVAP tank pressure control solenoid valve. Refer to Evaporative Emission Tank Pressure Control Solenoid Valve Replace . Is the action complete? | -- | -- | |||||||||||||
34 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |||||||||||||
Are any DTCs displayed on the scan tool? | -- | System OK |
