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 1.02 mm (0.040 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 pressure (FTP) sensor signal in order 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

    • DTCs P0450, P0451, P0452, and P0453 are not set.
    • The barometric pressure (BARO) indicates that the altitude is less than 2,400 meters (7,872 feet).
    • The battery voltage is at least 11 volts.
    • The fuel level is approximately 10-90 percent--no excess fuel slosh is indicated.
    • The engine coolant temperature (ECT) sensor and the intake air temperature (IAT) sensor are near the same temperature at engine start.
    • The ECT and the IAT are between 10°C (50°F) and 32°C (89°F) at engine start.
    • The engine has been operating for at least 50 minutes.
    • The vehicle is operated at steady speeds.
    • The EVAP canister purge valve has been open and the fuel tank pressure (FTP) sensor indicates a negative pressure in the fuel tank of at least -18 mm Hg (-9.63 inches H2O).
    • DTC P0442 runs once per drive cycle when the above conditions are met.

Conditions for Setting the DTC

Either of the fallowing conditions are present:

    • Condition 1--The FTP sensor determines that the EVAP system is unable to achieve a vacuum, indicating a large leak.
    • Condition 2--The EVAP system can achieve vacuum, but a vacuum decay that is 0.040 inch or more is detected during the diagnostic test.

Action Taken When the DTC Sets

    • The PCM illuminates the malfunction indicator lamp (MIL) after 2 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 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.
    • A DTC will clear after 40 consecutive warm-up cycles have occurred without a fault.
    • A DTC can be cleared by using the scan tool Clear Information function.

Diagnostic Aids

    • The EVAP control system is required to detect evaporative emission fuel system leaks as small as 0.020 inch, between the fuel fill cap, and the purge solenoid.
    • 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.
    • 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.
    • In order to improve the visibility of the smoke exiting the EVAP system, observe the suspected leak area from different angles with the J 41413-SPT .
    • 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.
    • 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.
    • 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 .
    • For intermittent conditions refer to Intermittent Conditions .

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. This test verifies that the EVAP purge solenoid is electrically functional.

  3. This test verifies that the EVAP vent solenoid is electrically functional.

  4. This test verifies that the EVAP pressure switching solenoid is electrically functional

  5. 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.

  6. 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.

  7. This step tests the functional operation of the EVAP pressure switching solenoid.

  8. This step tests the functional operation of the EVAP vent solenoid.

  9. This step tests the functional operation of the EVAP vent solenoid.

  10. This step tests the functional operation of the EVAP purge solenoid.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views

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, P0451, P0452, or P0453 present?

--

Go to Diagnostic Trouble Code (DTC) List

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 44

Go to Step 5

5

Command the EVAP purge solenoid ON and OFF with the scan tool. Refer to Scan Tool Output Controls .

Do you hear or feel a click as the EVAP purge solenoid is commanded ON and OFF?

--

Go to Step 6

Go to Step 8

6

Command the EVAP vent solenoid ON and OFF with the scan tool.

Do you hear or feel a click as the EVAP vent solenoid is commanded ON and OFF?

--

Go to Step 7

Go to Step 10

7

Command the EVAP pressure switching solenoid ON and OFF with the scan tool.

Do you hear or feel a click as the EVAP pressure switching solenoid is commanded ON and OFF?

--

Go to Step 14

Go to Step 12

8

  1. Disconnect the EVAP purge solenoid.
  2. Turn ON the ignition, with the engine OFF.
  3. Connect a test lamp between the ignition positive voltage circuit of the EVAP purge solenoid and a known good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 35

9

  1. Connect a test lamp between the ignition positive voltage circuit of the EVAP purge solenoid and the control circuit of the EVAP purge solenoid. Refer to Circuit Testing in Wiring Systems.
  2. Command the EVAP purge solenoid ON with a scan tool.

Does the test lamp illuminate when the EVAP purge solenoid is commanded ON and turn OFF when the EVAP purge solenoid is commanded OFF?

--

Go to Step 27

Go to Step 24

10

  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the EVAP vent solenoid.
  3. Connect a test lamp between the ignition positive voltage circuit of the EVAP vent solenoid and a known good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 11

Go to Step 35

11

  1. Connect a test lamp between the ignition positive voltage circuit of the EVAP vent solenoid and the control circuit of the EVAP vent solenoid. Refer to Troubleshooting with a Test Lamp in Wiring Systems.
  2. Command the EVAP vent solenoid ON, with a scan tool.

Does the test lamp illuminate when the EVAP vent solenoid is commanded ON and turn OFF when the EVAP vent solenoid is commanded OFF?

--

Go to Step 28

Go to Step 25

12

  1. Turn ON the ignition, with the engine OFF.
  2. Disconnect the EVAP pressure switching solenoid.
  3. Connect a test lamp between the ignition positive voltage circuit of the EVAP pressure switching solenoid and a known good ground. Refer to Troubleshooting with a Test Lamp in Wiring Systems.

Does the test lamp illuminate?

--

Go to Step 13

Go to Step 35

13

  1. Connect a test lamp between the ignition positive voltage circuit of the EVAP pressure switching solenoid and the control circuit of the EVAP pressure switching solenoid. Refer to Troubleshooting with a Test Lamp in Wiring Systems.
  2. Command the EVAP pressure switching solenoid ON, with a scan tool.

Does the test lamp illuminate when the EVAP pressure switching solenoid is commanded ON and turn OFF when the EVAP pressure switching solenoid is commanded OFF?

--

Go to Step 29

Go to Step 26

14

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 44

Go to Step 15

15

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

Is the FTP sensor near the specified value?

0.17 mm Hg (0.09 in H2O)

Go to Step 16

Go to Step 30

16

  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 Fuel Tank Pressure Sensor parameter more than the second specified value?

24.28 mm Hg (13 in H2O)

9.34 mm Hg (5 in H2O)

Go to Step 17

Go to Step 19

17

  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 21

Go to Step 18

18

  1. Inspect the vapor hoses on both sides of the EVAP pressure switching solenoid for a blockage or a restriction.
  2. Repair any obstruction or restriction as necessary.

Did you find and correct a condition?

--

Go to Step 44

Go to Step 41

19

Disconnect the vapor line at the EVAP canister.

Does the J 41413-200 gage indicate the specified value?

0 mm Hg (0 in H2O)

Go to Step 36

Go to Step 20

20

Disconnect the purge line at the EVAP canister.

Does the J 41413-200 gage indicate the specified value?

0 mm Hg (0 in H2O)

Go to Step 23

Go to Step 37

21

  1. Disconnect the EVAP solenoid vent hose at the EVAP canister.
  2. Command the EVAP vent solenoid ON, closed
  3. Install a hand vacuum pump to the vent hose, and apply a vacuum.

Did you achieve a vacuum?

--

Go to Step 22

Go to Step 32

22

Command the EVAP vent solenoid OFF, open.

Does the vacuum decrease?

--

Go to Step 23

Go to Step 33

23

  1. Disconnect the purge hose of the EVAP canister purge solenoid at the solenoid.
  2. Connect a hand vacuum pump to the purge port of the EVAP canister purge solenoid.
  3. Apply a vacuum with the vacuum pump.
  4. You should be able to obtain and hold a vacuum.
  5. Observe the vacuum gauge of the vacuum pump while commanding the EVAP purge solenoid ON, OPEN, with the scan tool.
  6. The vacuum gauge should drop when the solenoid is commanded ON.

Did the purge solenoid pass both tests?

--

Go to Step 34

Go to Step 39

24

Test the control circuit of the EVAP purge solenoid for an open, short to ground, or for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 31

25

Test the control circuit of the EVAP vent solenoid for an open, short to ground, or a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 31

26

Test the control circuit of the EVAP pressure switching solenoid for an open, short to ground or for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 31

27

Test for an intermittent and for a poor connection at the EVAP canister purge solenoid. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 39

28

Test for an intermittent and for a poor connection at the EVAP vent solenoid. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 40

29

Test for an intermittent and for a poor connection at the EVAP pressure switching solenoid. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 41

30

Test for an intermittent and for a poor connection at the FTP sensor. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 42

31

Test for an intermittent and for a poor connection at the control module. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 43

32

  1. Inspect for a leak source in the EVAP solenoid vent hose.
  2. Repair as necessary.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 40

33

  1. Inspect for a pinched or obstructed EVAP vent hose
  2. Repair as necessary.

Did you find and correct the condition?

--

Go to Step 44

Go to Step 40

34

Inspect for a faulty EVAP canister. Refer to Evaporative Emission Control System Diagnosis .

Did you replace the EVAP canister?

--

Go to Step 44

Go to Step 38

35

  1. Repair the open or short to ground in the ignition positive voltage circuit of the EVAP solenoid. Refer to Wiring Repairs in Wiring Systems.
  2. Replace the fuse as necessary.

Did you complete the repair?

--

Go to Step 44

--

36

Repair the restriction in the EVAP vapor pipe.

Did you complete the repair?

--

Go to Step 44

--

37

Repair the restriction in the EVAP purge pipe.

Did you complete the repair?

--

Go to Step 44

--

38

Was a DTC P0446 also set?

--

Go to DTC P0446

Go to Diagnostic Aids

39

Replace the EVAP purge solenoid. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement .

Did you complete the replacement?

--

Go to Step 44

--

40

Replace the EVAP vent solenoid. Refer to Evaporative Emission Canister Vent Solenoid Valve Replacement .

Did you complete the replacement?

--

Go to Step 44

--

41

Replace the pressure switching solenoid. Refer to Evaporative Emission Pressure Switching Solenoid Replacement .

Did you complete the replacement?

--

Go to Step 44

--

42

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

Did you complete the replacement?

--

Go to Step 44

--

43

Replace the control module. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 44

--

44

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. Plug the drain hose of the EVAP canister using the J 41413-301 plug. Refer to Evaporative Emissions Hose Routing Diagram .
  3. Turn the nitrogen/smoke valve to NITROGEN.
  4. Pressurize the EVAP system to the specified value.
  5. Observe the J 41413-200 pressure/vacuum gage for 5 minutes.

Does the pressure/vacuum gage remain constant?

9.34 mm Hg (5 in H2O)

Go to Step 45

Go to Step 14

45

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