GM Service Manual Online
For 1990-2009 cars only

System Description

When running the DTC P0442 Evaporative Emission (EVAP) System Small Leak Detected diagnostic detects evaporative emission system leaks as small as 0.51 mm (0.020 inch). The powertrain control module (PCM) will command the EVAP vent valve ON, CLOSED, and the purge valve and the vacuum pressure switching valve ON, OPEN, with the engine running. This allows engine vacuum into the EVAP system. The PCM then commands the purge valve OFF, CLOSED, sealing the system. The PCM then monitors the fuel tank vapor pressure sensors signal to determine if there is vacuum decay. A rise or increase just above normal pressure indicates there is a small leak in the evaporative emission system. If the PCM detects the vacuum level was not achieved and vacuum decay was within a specified value a DTC P0442 will set.

Conditions for Running the DTC

    â€¢ The barometric pressure (BARO) is more than 75 kPa.
    â€¢ The fuel level is between 25-75 percent.
    â€¢ The ECT sensor and the intake air temperature (IAT) sensor are near the same temperature at engine start.
    â€¢ The ECT sensor is at least 74°C (165°F) after engine warm up.
    â€¢ The vehicle has been driven for at least 20 minutes.
    â€¢ The EVAP canister purge valve has been open and the fuel tank pressure (FTP) sensor indicates a negative pressure in the fuel tank.

Conditions for Setting the DTC

The EVAP system can achieve vacuum, but a vacuum decay is detected during the diagnostic test.

Action Taken When the DTC Sets

    â€¢ The PCM illuminates the malfunction indicator lamp (MIL) after 2 consecutive ignition cycles in which the diagnostic runs with the fault active.
    â€¢ 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

    â€¢ The PCM turns OFF the MIL on the third consecutive trip cycle during which the diagnostic has been run and the fault condition is no longer present.
    â€¢ A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.
    â€¢ A DTC can be cleared by using the scan tool Clear Information function.

Diagnostic Aids

    â€¢ The EVAP control system is required to detect evaporative emission fuel system leaks as small as 0.5mm (0.020) inch, between the fuel fill cap, and the purge solenoid.
    â€¢ To help locate intermittent leaks, use the J 41413-200 Evaporative Emissions System Tester (EEST) to introduce smoke into the EVAP system. Move all EVAP components while observing smoke with the J 41413-SPT High Intensity White Light.
    â€¢ A temporary blockage in the EVAP purge solenoid, purge pipe or EVAP canister could cause an intermittent condition. Inspect and repair any restriction in the EVAP system.
    â€¢ To improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles with the J 41413-SPT .
    â€¢ The test for leaks with smoke is performed with the system subjected to positive pressure. The trouble code diagnostic tests for a leak with vacuum or negative pressure. Perform the Purge/Seal test with the scan tool in order to test for leaks using vacuum pressure. Refer to Purge/Seal Function in Service Bay Test. If the Purge/Seal test fails, inspect the EVAP system o-ring seals for failure. O-ring seals can provide a good seal with pressure applied in one direction, but leak when the pressure is applied in the opposite direction.
    â€¢ Operating the vehicle in Check Mode will increase the ability of the powertrain control (PCM) module to detect engine control system malfunctions. Refer to Check Mode in Service Bay Test.
    â€¢ For intermittent conditions refer to Intermittent Conditions.
    â€¢ Reviewing the Freeze Frame 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

The numbers below refer to the step numbers on the diagnostic table.

  1. This step verifies that the DTC P0442 is captured in the freeze frame/failure record list. When multiple EVAP system DTCs are set, the DTC stored in the freeze frame/failure record is the best diagnostic starting point.

  2. The fuel filler pipe has two vent lines that allow for recirculation of fuel vapors between the fuel filler pipe and the fuel tank. Because of these vent lines the EEST can be connected to the EVAP service port for leak detection. Waiting until smoke is seen before plugging the EVAP canister drain hose speeds up the filling of the canister with smoke. Introducing smoke in between 60 second intervals of Nitrogen will speed up the filling of smoke in the fuel tank and filler pipe vapor space. This occurs because the pressure at which Nitrogen gas is applied is greater than the pressure at which smoke is introduced. The Nitrogen gas pushes the smoke that was just introduced through the canister and into the fuel tank. The EVAP vent solenoid DOES NOT have to be turned ON in order to test for leaks. A one way check valve located in the vent port of the EVAP canister provides containment of smoke and pressure within the EVAP system.

  3. This test verifies that the fuel tank pressure (FTP) sensor is accurate. An FTP sensor that does not correctly respond to vacuum, or pressure may cause this DTC to set.

  4. This step verifies whether a leak in the EVAP system still exists. If the flow gage on the EEST and/or the scan tool pressure reading remain constant, there is no external leak. If the EEST gage indicates flow, or the scan tool pressure reading decreases, there is still an external leak in the EVAP system.

  5. This step tests the fuel tank assembly for leaks with the tank removed from the vehicle. The J 41413-300 EVAP Cap and Plug Kit enables you to use smoke to test for a leak on the portions of the fuel tank that are not visible when installed in the vehicle.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics and Evaporative Emissions Hose Routing Diagram

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Install a scan tool.
  2. Check for DTCs.

Is a DTC P0450 or P0451 present?

--

Go to DTC P0450 or DTC P0451

Go to Step 3

3

  1. Review the Freeze Frame/Failure Records.
  2. Diagnose the DTC captured in the Freeze Frame/Failure records first.

Is DTC P0442 captured in the Freeze Frame/Failure records?

--

Go to Step 4

Go to Diagnostic Trouble Code (DTC) List

4

  1. Inspect the EVAP system for the following conditions:
  2. • A loose, missing, or damaged service port schrader valve
    • A loose, incorrect, missing, or damaged fuel fill cap
    • A damaged EVAP purge solenoid
  3. Raise the vehicle on a hoist. Refer to Lifting and Jacking the Vehicle in General Information.
  4. Inspect the EVAP system for the following conditions:
  5. • Any disconnected, improperly routed, kinked, or damaged EVAP pipes and hoses
    • A damaged EVAP vent solenoid or EVAP canister

Did you find and correct the condition?

--

Go to Step 10

Go to Step 5

5

Important: Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. System flow will be less with higher temperatures.

  1. Connect the nitrogen/smoke supply hose of the J 41413-200 Evaporative Emission System Tester (EEST) to the EVAP service port.
  2. Turn the nitrogen/smoke valve on the control panel to SMOKE.
  3. Use the remote switch to introduce smoke into the EVAP system.
  4. Continue to introduce smoke until a steady flow of smoke is seen exiting the EVAP canister drain hose. Refer to Evaporative Emissions Hose Routing Diagram
  5. Plug the drain hose of the EVAP canister using the J 41413-301 plug. Refer to Evaporative Emissions Hose Routing Diagram
  6. Turn the nitrogen/smoke valve on the control panel to NITROGEN.
  7. Use the remote switch to introduce Nitrogen gas into the EVAP system for 60 seconds.
  8. Inspect the entire EVAP system for exiting smoke with the J 41413-SPT .
  9. Continue to introduce smoke, then Nitrogen, at 60 second intervals, until the source of the leak has been located.

Did you locate and repair a leak source?

--

Go to Step 10

Go to Step 6

6

  1. Remove the fuel fill cap.
  2. Observe the FTP in H20 with the scan tool.

Is the FTP in H20 near the specified value?

0.17 mm Hg (0.09 in H2O)

Go to Step 7

Go to Step 9

7

  1. Install the fuel fill cap on the fuel fill pipe.
  2. Turn the J 41413-200 nitrogen/smoke valve on the control panel to NITROGEN.
  3. Use the J 41413-200 to pressurize the EVAP system to the first specified value.

Is the FTP parameter more than the second specified value?

18.68 mm Hg (10 in H2O)

9.34 mm Hg (5 in H2O)

Go to Step 8

Go to Step 9

8

  1. Use the remote switch to stop introducing nitrogen into the EVAP system.
  2. Disconnect the purge hose at the EVAP canister purge solenoid.
  3. Command the EVAP pressure switching solenoid ON.

Is the FTP Sensor parameter less than the specified value?

1.86 mm Hg (1 in H2O)

Go to Step 10

Go to Step 9

9

Replace the FTP sensor. Refer to Fuel Tank Pressure Sensor Replacement.

Did you complete the replacement?

--

Go to Step 12

--

10

Important: Ensure that the vehicle underbody temperature is similar to the ambient temperature and allow the surrounding air to stabilize before starting the diagnostic procedure. System flow will be less with higher temperatures.

  1. Remove the fuel fill cap and install the J 41415-30 Fuel Tank Cap Adapter.
  2. Connect the nitrogen/smoke supply hose of the J 41413-200 to the correct fuel tank cap adapter.
  3. Plug the drain hose of the EVAP canister using the J 41413-301 plug. Refer to Evaporative Emissions Hose Routing Diagram.
  4. Turn the nitrogen/smoke valve to NITROGEN.
  5. Pressurize the EVAP system until the flow gage indicator on the EEST has dropped to a no flow position.
  6. Observe the flow gage for 5 minutes.

Did the flow gage indicator remain in the no flow position?

--

Go to Step 12

Go to Step 11

11

Inspect the fuel tank and component parts for leaks. Refer to Fuel Tank Leak Test.

Did you find and correct a condition?

--

Go to Step 12

Go to Diagnostic Aids

12

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK