GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Century 🢒 DTC 🢒 DTC P0442 Evaporative Emission (EVAP) System Small Leak Detected

Refer to Emission Hose Routing Diagram,

EVAP Control System Overview


Object Number: 200517 Size: LF
(1)EVAP Vent Valve/Solenoid
(2)EVAP Vent Valve/Solenoid Ignition Feed Circuit Terminal
(3)EVAP Vent Valve/Solenoid Control Circuit Terminal
(4)EVAP Vent Valve/Solenoid Filter
(5)EVAP Vapor Lines
(6)Fuel Tank Pressure Sensor
(7)Fuel Tank Pressure Sensor Ground Circuit Terminal
(8)Fuel Tank Pressure Sensor Signal Circuit Terminal
(9)Fuel Tank Pressure Sensor Circuit 5 Volt Reference Circuit Terminal
(10)Fuel Filler Pipe
(11)Check Valve (Spitback)
(12)Modular Fuel Sender Assembly
(13)Fuel Limiter Vent Valve (FLVV)
(14)Pressure/Vacuum Relief Valve (Optional)
(15)EVAP Canister
(16)EVAP Canister Purge Valve/Solenoid Ignition Feed Circuit Terminal
(17)EVAP Canister Purge Valve/Solenoid Control Circuit Terminal
(18)Intake Manifold Vacuum Source
(19)EVAP Canister Purge Valve/Solenoid
(20)EVAP Service Port

EVAP System Operation

The EVAP SMALL LEAK TEST is based on applying vacuum to the EVAP system and monitoring vacuum decay. The PCM monitors vacuum level via the Fuel Tank Pressure sensor input. At an appropriate time, the EVAP purge solenoid and the EVAP vent solenoid are turned on allowing engine vacuum to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP purge solenoid is turned off, sealing the system. A leak is detected by monitoring for a decrease in vacuum level over a given time period, all other variables remaining constant. A small leak in the system will cause DTC P0442 to be set.

Conditions for Running the DTC
    •  No TP sensor, ODM, IAT sensor, or MAP sensor DTCs set.
    •  The DTC P0440 diagnostic test has passed.
    • Startup engine coolant temperature is not more than 4°C and 30°C (40°F 86°F).
    • Startup engine is not more than 8°C (14°F).
    • Startup Intake air temperature not more than 2°C and 30°C (40°F and 86°F).
    • Startup intake air temperature not more than 2°C (4°F).
    • Fuel tank level is between 15% and 85%.
    • BARO is greater than 75kPa.

Conditions for Setting the DTC

A vacuum decay condition indicating a small leak is detected during the diagnostic test.

Action Taken When the DTC Sets

Important: Although these diagnostics are considered type A, they act like type B diagnostics under certain conditions. Whenever the EVAP diagnostics report that a system has passed, or if the battery has been disconnected, the diagnostic must fail during 2 consecutive cold start trips before setting a DTC. The initial failure is not reported to the diagnostic executive or displayed on a scan tool. A passing system always reports to the diagnostic executive immediately.

    • The PCM will illuminate the MIL during the first 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 Fail Records data.

Conditions for Clearing the MIL/DTC
    • The PCM will turn the MIL OFF 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 Clear Info function or by disconnecting the PCM battery feed.

Diagnostic Aids

Check for the following conditions:

    •  Cracked or punctured EVAP canister.
    •  Damaged source vacuum line, EVAP purge line, EVAP vent hose or fuel tank vapor line.
    •  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 to the EVAP vent solenoid EVAP purge solenoid and the fuel tank pressure sensor for an intermittent open or short circuit.

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:

  1. The powertrain OBD System Check promps you to complete some of the basic checks and store the freeze frame and failure records data on the Scan Tool if applicable.

    2.

  2. If a vent valve or EVAP purge valve electrical malfunction is present, the purge system will not operate correctly. Repairing the electrical malfunction that caused the additional DTC to set will very likely correct the condition that set this DTC.

    3.

  3. Checks for a fuel tank pressure sensor stuck high condition. The fuel tank pressure must be relieved by removing the canister line from the fuel tank or EVAP canister. The fuel fill cap will not relieve the tank due to a check valve in the filler neck. the check valve seals when pressure is applied to prevent vapors from escaping through the filler neck. The Scan Tool should read within 1.0 in. H2O of the specified value.

    4.

  4. Verifies that the fuel tank pressure sensor accurately reacts to EVAP system pressure changes. The EVAP station is pressurizing a sensor that normally reads vacuum. The tech II reads high pressure at 0 volts and high vacuum at 5 volts. The Tech II can only read a max pressure of 6.0 inches of H2O (0 Volts). However the EVAP Service station can pressurize the system to much higher pressures. The Scan Tool value should be within 0.5 of the specified value.

    5.

  5. Checks for a small leak in the EVAP system.

    6.

  6. Checks for a leak in the Canister, vent line, or a leaking EVAP Vent Valve.

    7.

  7. Checks for a leaking or stuck open EVAP canister purge valve/solenoid. The scan tool should read within 1.0 in. HG of the specified value.

    8.

  8. The EVAP station is pressurizing a sensor that normally reads vacuum. The Tech II reads high pressure at 0 volts and high vacuum at 5 volts. The Tech II can only read a max pressure of 6.0 inches of H2O (0 Volts). However the EVAP Service station can pressurize the system to much higher pressures. The Scan Tool value should be within 0.5 of the specified value.

DTC P0442 - EVAP System

Step

Action

Value(s)

Yes

No

1

Was the Powertrain OBD System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Important: :  Visually/physically inspect for the following conditions:

   •  Vacuum or purge lines disconnected. Refer to Emission Hose Routing Diagram .
   •  Loose or missing fuel fill cap.

Is DTC P0443 Evaporative Emission (EVAP) Purge Solenoid Control Circuit or DTC P0449 Evaporative Emission (EVAP) Vent Valve Solenoid Control Circuit also set?

--

Go to DTC P0443 Evaporative Emission (EVAP) Purge Solenoid Control Circuit or DTC P0449 Evaporative Emission (EVAP) Vent Solenoid Control Circuit

Go to Step 3

3

  1. Ignition switch OFF.
  2. Remove the EVAP canister line from the EVAP canister purge valve. This will relieve the fuel tank pressure.
  3. Ignition switch ON, Engine OFF.
  4. Observe Fuel Tank Pressure on the scan tool.

Is the Fuel Tank Pressure near the specified value?

0 in. H2O

Go to Step 4

Go to Step 15

4

Important: :  Before continuing with diagnosis, zero the EVAP Pressure and Vacuum (inches of H2O) gauges on the J 41413 EVAP Pressure/Purge Diagnostic Station.

Important:: Do not exceed the pressure in the specified value .

  1. Ignition Switch OFF.
  2. Reconnect all EVAP hardware that was previously disconnected.
  3. Connect the EVAP Station to the EVAP service station.
  4. Ignition Switch ON, Engine Off.
  5. Capture Fail Record data for DTC P0440 and clear DTCs.
  6. Using the scan tool, EVAP Purge/Seal, select seal option to seal the EVAP System.
  7. Attempt to pressurize the system to the specified value by slowly turning the EVAP Service Station rotary switch to the Pressure position. (Monitor the pressure with the gauge on the cart with the rotary switch to the OFF/Hold position).
  8. Observe Fuel Tank Pressure on the scan tool.

Is the Fuel Tank Pressure near the specified value?

5 in. H2O

Go to Step 5

Go to Step 7

5

Important: Do not exceed the pressure in the specified (higher) value

  • Increase pressure to the first specified (higher) value by slowly turning the EVAP Service Station rotary switch to the Pressure position. (Monitor the pressure with the gauge on the cart with the rotary switch in the 'Off/Hold position)

Does the EVAP Pressure decrease to less than the second specified (lower) value within 2 minutes with the rotary switch in the "Off/Hold position?

15 in. H2O

10 in. H2O

Go to Step 6

Go to Diagnostic Aids

6

  1. Disconnect the fuel tank vapor line and the EVAP purge line from the EVAP canister.
  2. Block the canister fitting for the fuel tank vapor line.
  3. Connect a hand vacuum pump to the canister port for the EVAP purge line.
  4. Ensure that the EVAP System is still sealed with the Tech II.
  5. Attempt to apply vacuum to the EVAP canister. The EVAP canister is large and may take time to achieve specified level.

Can vacuum be maintained at the specified value?

5 in. Hg

Go to Step 9

Go to Step 8

7
  1. Visually/physically check for the following conditions:
    2. •  Restricted fuel tank vapor line.
    •  Restricted EVAP purge line.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage

8
  1. Visually/physically check for the following conditions:
    2. •  Damaged Fresh Air Vent Hose.
    • Damaged EVAP canister .
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

Go to Step 13

9
  1. Visually/physically check for the following conditions:
    2. •  Leaking fuel tank vapor line.
    •  Damaged EVAP purge line.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 16

Go to Step 10

10

  1. Disconnect the engine vacuum Purge line from the EVAP canister purge valve.
  2. Connect the EVAP Service Station (Hg) Vacuum Gauge to the Purge Valve/Solenoid, canister side.
  3. Ignition switch ON, Engine Off
  4. Using the Scan Tool, EVAP Purge/Seal, Select the seal option to seal the EVAP System.
  5. Start the engine and idle.
  6. Run the engine from 1200 -1500 RPM and observe vacuum level.

Is vacuum level near the specified value?

0 in. Hg

Go to Step 12

Go to Step 11

11

Is the action complete?

--

Go to Step 16

--

12

Important: Do not exceed the 15 in. H2O pressure in the specified value.

  1. Reconnect all EVAP hardware that was previously disconnected.
  2. Using the scan tool, EVAP Purge/Seal, select Seal Option to seal the EVAP System.
  3. With the EVAP pressure/purge diagnostic station connected to the Fuel Tank Cap Adaptor, continuously attempt to pressurize the EVAP system to the specified value by leaving the EVAP pressure/purge diagnostic station control knob in the pressurize position
  4. Using the ultrasonic leak detector J 41416, locate and repair leak in EVAP system. It may be necessary to partially lower the fuel tank to examine the top tank connections.
  5. Replace the faulty part(s).

Is the action complete?

15 in. H2O

Go to Step 16

--

13

Is the action complete?

--

Go to Step 16

--

14
  1. Check for a kinked or restricted canister purge line between the EVAP canister purge valve and EVAP canister.
  2. Repair the canister purge as necessary.

Is action complete?

0 in. H2O

Go to Step 16

--

15
  1. Ignition switch OFF.
  2. Remove the EVAP canister line from the fuel tank or EVAP canister. This will relieve the fuel tank pressure.
  3. Ignition switch ON, Engine OFF.
  4. Observe Fuel Tank Pressure on the scan tool.

Is the Fuel Tank Pressure near the specified value?

0 in. H2O

Go to Step 14

Go to DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage

16

Important:: Do not exceed the pressure in the specified value .

  1. Reconnect all EVAP hardware that was previously disconnected.
  2. Ignition switch On, Engine Off.
  3. Using scan tool, Purge/Seal, select the seal option to seal the EVAP System.
  4. Pressurize the system to the first specified (higher) value by slowly turning the EVAP Service station rotary switch to the Pressure position. (Monitor the pressure with the gauge on the cart with the rotary switch in the OFF/Hold position).

Does the EVAP pressure decrease to less than the second specified (lower) value within 2 minutes with the rotary switch in the 'Off/Hold' position?

15 in. H2O

10 in. H2O

Go to Step 3

System OK