GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 LeSabre 🢒 Body and Accessories 🢒 Wiring Systems 🢒 Evaporative Emission Control System Diagnosis

Refer to Emission Hose Routing Diagram .

System Description

The EVAP canister purge valve allows manifold vacuum to purge the canister. The powertrain control module (PCM) supplies a ground to energize the purge valve . The EVAP purge valve control is pulse width modulated (PWM), or turned ON and OFF, several times a second. The pulse width is determined by the engine operating conditions including the load, the throttle position, the coolant temperature, and the ambient temperature. The duty cycle is calculated by the PCM and the output is commanded when the appropriate conditions have been met.

The EVAP Vent valve is used to seal the EVAP system during diagnostic tests. The fuel tank pressure sensor is used to monitor vacuum in the system during the diagnostic tests.

A stuck closed EVAP canister purge valve, stuck open EVAP vent valve, disconnected or damaged EVAP purge line or vent hose, or a leaking fuel cap or fill neck should set a DTC P0440. A small leak in the EVAP system should set a DTC P0442. An EVAP vent valve stuck closed, a restricted vent hose, or a blocked EVAP canister should set a DTC P0446. A continuous purge condition with no purge commanded by the PCM (EVAP purge valve stuck open or leaking) should set a DTC P1441. Refer to Diagnostic Trouble Code (DTC) List/Type for further diagnostic procedures regarding the EVAP system.

The EVAP system includes the following components:

    • The EVAP canister
    • The EVAP canister purge valve
    • The EVAP vent valve
    • The EVAP vapor pipes
    • The EVAP purge pipes
    • The EVAP fresh air vent hose
    • The fuel tank
    • The fuel pipes and hoses
    • The fuel fill cap
    • The fuel fill pipe

Diagnostic Aids

Check for the following conditions:

    •  A cracked or punctured EVAP canister
    •  A damaged or disconnected source vacuum line, EVAP purge line, vent hose, or fuel tank vapor line.
    • A poor connection at the PCM.
    •  Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    •  A damaged harness. Inspect the wiring harness to the EVAP vent valve, the EVAP purge valve, and the fuel tank pressure sensor for an intermittent open or short circuit.
    •  A kinked, pinched, or plugged vacuum source, EVAP purge, or fuel tank vapor line. Verify that the lines are not restricted.
    • Any carbon being released into the system.

EVAP Control System Diagnosis

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Did any other DTC set?

--

Go to the applicable DTC tables

Go to Step 3

3

Inspect the EVAP system for the following conditions:

    • A loose,incorrect, defective, or missing fuel fill cap
    • An improperly routed, kinked, or damaged EVAP system purge or vapor pipes
    • A pinched off or damaged fresh air vent hose
    • Any damaged EVAP system component
    • A loose, missing, or damaged service port dust cap and/or Schrader valve

Did you find and correct the condition?

--

Go to Step 9

Go to Step 4

4
  1. Disconnect the EVAP vapor pipe from the fuel tank or the EVAP canister.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Fuel Tank Pressure parameter.

Is the fuel tank pressure near the specified value?

0 in H2O

Go to Step  5

Go to DTC P0453 Fuel Tank Pressure Sensor Circuit High Voltage

5
  1. Reconnect all EVAP hardware that was previously disconnected.
  2. Install theJ 41415-40 fuel tank cap adapter to the fuel fill neck and the fuel fill cap.
  3. Connect the J 41413 EVAP pressure/purge diagnostic station to the fuel tank cap adaptor.
  4. Use a scan tool to seal the EVAP system.

    5. Important: DO NOT exceed the pressure in the specified value.

  5. Use the EVAP station to pressurize the system to the specified value by slowly turning the rotary switch to the Pressure position.

Did you achieve the specified value?

1.25 kPa (5 in H2O)

Go to Step  6

Go to DTC P0440 Evaporative Emission (EVAP) System

6

Use the EVAP service station to maintain fuel tank pressure at the specified value.

Is the fuel tank pressure at the specified value?

1.25 kPa (5 in H2O)

Go to Step 7

Go to DTC P0452 Fuel Tank Pressure Sensor Circuit Low Voltage

7

With a scan tool, command the vent valve OFF.

Does the pressure decrease to near the specified value within 2 minutes with the rotary switch in the Off/Hold position?

0 kPa (0 in H2O)

Go to Step 8

Go to DTC P0446 Evaporative Emission (EVAP) Vent System Performance

8
  1. With the EVAP station, increase the fuel tank pressure to the first specified value.
  2. With a scan tool, observe the Fuel Tank Pressure parameter.

Does the scan tool indicate a fuel tank pressure decrease to the second specified value within 15 seconds?

1.25 kPa (5 in H2O)

0 kPa (0 in H2O)

Go to DTC P1441 Evaporative Emission (EVAP) System Flow During Non-Purge

Go to Step  9

9
  1. Reconnect all EVAP hardware that was previously disconnected.
  2. Turn ON the ignition, with the engine OFF.
  3. With scan tool, select the Seal option in order to seal the EVAP system.

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

  4. With the EVAP station, pressurize the system to the first specified value by slowly turning the rotary switch to the Pressure position.
  5. 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 value within 2 minutes?

15 in H2O

10 in H2O

Go to DTC P0442 Evaporative Emission (EVAP) System Small Leak Detected

System OK