DTC P0440 Evaporative Emission (EVAP) System. Pontiac Firefly (Canada) 1996

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1996 🢒 Firefly (Canada) 🢒 DTC 🢒 DTC P0440 Evaporative Emission (EVAP) System

Schematic Reference: Engine Controls Schematics

Circuit Description

The EVAP control system leak detection diagnostic strategy is based on applying vacuum to the EVAP system and monitoring vacuum decay. The 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 EVAP control 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

•	EVAP Tank Pressure Control Valve

•	EVAP canister

•	Purge lines

•	EVAP canister purge valve

Conditions for Running the DTC

•	Engine coolant temperature is 70°C to 110°C (158°F to 230°F).

•	Intake air temperature is -10°C to 70°C (14°F to 158°F).

•	Barometric pressure is greater than 75 kPa.

•	Fuel tank level is between 25 and 75%.

•	The DTC P0455 diagnostic has run.

Conditions for Setting the DTC

The change in the fuel tank pressure is greater than the specified value during a specified time interval.

Action Taken When the DTC Sets

•	The PCM illuminates the malfunction indicator lamp (MIL) after two consecutive ignition cycles in which the diagnostic runs with the fault active.

•	The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC

•	The MIL turns OFF after three consecutively passing trips without a fault present.

•	A History DTC clears after 40 consecutive warm-up cycles without a fault.

•	Use the scan tool Clear DTC Information function in order to clear the DTC.

Diagnostic Aids

The EVAP Purge diagnostic checks for many of the faults that can cause a DTC P0440 to set. Perform the scan tool Clear DTC Information function. 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 EVAP Purge diagnostic is indicating OK at this time and the cause of the DTC P0440 is intermittent.

An intermittent DTC P0440 can be caused by a faulty EVAP canister. An EVAP canister that has released carbon particles can cause the EVAP canister purge solenoid valve to fail (leak) intermittently. Inspect the EVAP purge system for carbon contamination before returning the vehicle to service. Refer to Evaporative Emission System Cleaning .

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.

A DTC P0440 can be caused by any of the following conditions:

•	Faulty or loose fuel cap

•	Damaged or disconnected source vacuum line

•	Damaged or leaking EVAP purge line

•	Damaged or leaking EVAP vent hose

•	Damaged or leaking fuel tank vapor line

•	Leaking or faulty EVAP canister purge valve

•	Leaking or faulty EVAP tank pressure control solenoid valve

•	Leaking or faulty EVAP vent solenoid

•	Leaking or faulty ORVR hoses and components

•	Blockage or restrictions in the EVAP system hoses, lines, or components

•	Cracked or punctured EVAP canister

•	Leaking fuel sender assembly O-ring

•	Leaking fuel tank or fuel filler neck

•	Faulty fuel tank pressure control valves

•	Faulty or erratic fuel tank pressure sensor

•	Fuel level sensor malfunction

A fuel level sensor that indicates an incorrect fuel level may cause the EVAP control system leak check diagnostic to run at the wrong time. An EVAP control system leak check diagnostic that runs at the wrong time may indicate a leak when none exists. Check the fuel level sensor accuracy by observing the fuel level sensor scan tool parameter before and after adding 3.8 liters (1 gallon) of fuel. The scan tool display should increase about 7% after adding the fuel. If a change of 7% is not indicated, check the fuel level sensor by performing the diagnostic for a DTC P0461. Refer to DTC P0461 Fuel Level Sensor Performance .

An intermittent malfunction may be caused by a fault in an EVAP control system electrical circuit. 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

•	Poor terminal to wire connections

•	Physical damage to the wiring harness

•	A broken wire inside the insulation

•	Corrosion of electrical connections, splices, or terminals

For functional checks of the EVAP control system components, refer to Evaporative Emission Control System Diagnosis .

If the DTC P0440 cannot be duplicated, 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.

The Powertrain OBD System Check prompts the technician to complete some basic checks and 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.

This step checks for other EVAP DTCs. Diagnose any DTCs other than a DTC P0455 first.

This step checks the components that supply manifold vacuum to the EVAP canister purge valve.

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, when engine speed is indicated, and until the engine has reached a normal operating temperature of at least 80°C (176°F).

This step checks the operation of the fuel tank pressure control valves. The fuel tank pressure control valves will regulate fuel tank pressure to approximately 18.6-25 mm Hg (10-14 in. H2O) when the EVAP canister vent solenoid is open (OFF). If the pressure indicated is less than the specified value after 2 minutes, there could be a faulty fuel tank pressure control valve, a faulty EVAP tank pressure control solenoid vacuum valve, or a system leak.

This step checks the operation of the EVAP tank pressure control solenoid valve. When the EVAP tank pressure control solenoid vacuum valve is turned ON (opened), the pressure in the fuel tank, bypasses the fuel tank pressure control valves, and drops to zero -- if the EVAP canister vent solenoid is open (OFF).

Use the ultrasonic leak detector in order to locate any leaks after pressurizing the EVAP system. If you were sent here from step 9, the leak is probably located between the fuel tank pressure control valve valves and the fuel tank, or the fuel tank itself. If you were sent here from step 10, the leak is probably located between the EVAP canister purge valve and the fuel tank pressure control valves.

A leaking, stuck open, or not operating EVAP canister vent solenoid will prevent the EVAP system from holding any pressure greater than 18.6 mm Hg (10 in. H2O). Inspect the EVAP canister vent solenoid electrical circuit for an open that could prevent the solenoid from turning ON.

This step checks for the proper operation of the fuel tank pressure sensor. With the fuel tank filler pipe open to the atmosphere, the fuel tank pressure sensor should read near zero. The fuel tank pressure sensor reading will vary with changes in atmospheric pressure. The specified value in step 13, is typical of atmospheric pressure near sea level. If the scan tool reading is significantly more or less than the specified value, the fuel tank pressure sensor may be faulty. The fuel tank pressure sensor is diagnosed in DTC P0450 EVAP System Pressure Sensor Circuit.

This step checks whether the malfunction that caused the DTC P0440 is still present. 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.

A short to ground will keep the EVAP tank pressure control solenoid vacuum valve open and cause the system to fail. Inspect the control circuit wiring and the PCM for a short to ground and repair as necessary. The EVAP tank pressure control solenoid valve output control is disabled by the PCM when any DTCs are stored, when engine speed is indicated, and until the engine has reached a normal operating temperature of at least 80°C (176°F).

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, when engine speed is indicated, and until the engine has reached a normal operating temperature of at least 80°C (176°F).

This step checks the operation of the EVAP tank pressure control solenoid vacuum valve. The EVAP tank pressure control solenoid vacuum valve output control is disabled by the PCM when any DTCs are stored, when engine speed is indicated, and until the engine has reached a normal operating temperature of at least 80°C (176°F).

This step checks for a stuck open or leaking EVAP tank pressure control solenoid valve.

This step checks the EVAP canister for blockage or restrictions.

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

Values

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Install a scan tool and check for DTCs.

Are any other EVAP codes set with the exception of a P0455?

Go to Appropriate DTC Tables

Go to Step 3

Visually inspect the entire evaporative system for the following:

•	Loose or faulty fuel filler (gas) cap

•	Loose hose connections

•	Damaged or deteriorated hoses

•	Clogged hoses

•	Missing or damaged components

•	Faulty terminal connections on all of the related components

Repair as necessary.

Was a repair necessary?