GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC K Pickup - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 Evaporative Emission Control System Diagnosis

Circuit Description

Applying a vacuum to the EVAP system and monitoring for a vacuum decay checks the evaporative emission system. The Control Module monitors the vacuum level through the fuel tank vacuum sensor signal. At an appropriate time, the EVAP canister purge valve and the EVAP vent solenoid turn ON, allowing the engine to draw a small vacuum on the entire evaporative emission system. After the desired vacuum level has been achieved, the EVAP canister purge valve turns OFF, sealing the system. A leak is detected by monitoring for a decrease in the vacuum level over a given time period, when all other variables remain constant. A leak, a blockage, or a malfunctioning component in the system causes a DTC to set.

Test Description

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

  1. This step checks the fuel tank pressure sensor at atmospheric pressure.

    2.

  2. This step determines if the EVAP system has a restriction or leak.

    3.

  3. This step deterimines if there is a restiction in the Fuel Tank Vapor Line or Canister.

    4.

  4. This step checks for a restriction in the EVAP Canister.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing the DTCs, use the scan tool to record the Freeze Frame and the Failure Records for reference. This data will be lost when the Clear Info function is used.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Is DTC P0446, P0452, or P0453 set?

--

Go to applicable DTC table

Go to Step 3

3

  1. Turn OFF the ignition.
  2. Install a scan tool.
  3. Remove the fuel cap.
  4. Turn ON the ignition.
  5. Observe the Fuel Tank Pressure on the scan tool.

Is the Fuel Tank Pressure at the specified value?

0 in. H2O ±1 in. H2O

Go to Step 4

Go to Fuel Tank Pressure Sensor Diagnosis

4

Important: Before continuing with the diagnosis, zero the EVAP Pressure and Vacuum gauges on the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413. Refer to the tool operating instructions.

Important: Make sure the fuel cap is secured properly. A poorly installed or loose fuel cap can cause DTC P0440.

  1. Install the fuel cap
  2. Connect the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413 to the EVAP service port.
  3. Using the scan tool, command the EVAP vent valve ON (Closed).
  4. Attempt to pressurize the EVAP system using the Cart.
  5. Monitor pressure using gauge on Cart for 2 minutes.

Can the specified value be obtained and held?

5 in. H2O

Go to Step 5

Go to Step 6

5

  1. Maintain fuel tank pressure at 5 inches of H2O (Turn the rotary switch on the cart to the HOLD position).
  2. Observe the Fuel Tank Pressure on the scan tool.

Is the Fuel Tank Pressure within the specified value?

5 in.H2O (±2 in.H2O

Go to Step 9

Go to Step 8

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 fitting for the EVAP Purge Line.
  4. Ensure that the EVAP Vent Valve is still commanded ON(Closed).
  5. Attempt to apply vacuum to the EVAP canister.

Can the specified value of vacuum be obtained and held?

5 in.Hg

Go to Step 12

Go to Step 7

7
  1. Leave system connected as in step 6.
  2. Disconnect the Vent hose at the Vent Valve.
  3. Plug end of the Vent hose.
  4. Using the hand vacuum pump apply vacuum up to the specified value.

Can the specified value of vacuum be obtained and held?

5 in.Hg

Go to Step 17

Go to Step 11

8

  1. Disconnect Fuel Tank Vapor Line from the Canister.
  2. Attempt to pressurize the EVAP system using the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413.
  3. Monitor pressure using gauge on cart.

Can the specified value of pressure be obtained and held?

5 in.H2O

Go to Step 18

Go to Step 15

9
  1. Disconnect Purge Line at the Canister.
  2. Connect the in. Hg vacuum gauge on the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413 to the Purge Line.
  3. Start engine
  4. Command EVAP Purge Solenoid Valve to 100%.

Is the vacuum gauge at or above the specified value?

12 in. Hg

Go to Diagnostic Aids

Go to Step 10

10
  1. Disconnect Purge Line from the Purge Solenoid Valve.
  2. Connect the in. Hg vacuum gauge on the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413 to the Purge Solenoid Valve.
  3. Start engine
  4. Command EVAP Purge Solenoid Valve to 100%.

Is the vacuum gauge at or above the specified value?

12 in. Hg

Go to Step 14

Go to Step 16

11

Check the Vent hose for possible cause of vacuum leak and repair as necessary.

Was a repair necessary?

--

Go to Step 19

Go to Step 18

12
  1. Check for the following:
    2. • Missing or faulty fuel cap.
    • Disconnected or leaking fuel Tank Vapor Line.
    • Disconnected or damaged EVAP Purge Line.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 19

Go to Step 13

13

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

  1. Using the scan tool, command the EVAP Vent Valve ON.
  2. With the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413 connected to the EVAP service port continuously attempt to pressurize the EVAP system by leaving the cart control knob in the pressurize position.
  3. Using the Enhanced EVAP Ultrasonic Leak Detector J 41416, locate the leak in the EVAP system. It may be necessary to partially lower the fuel tank in order to examine the connections on the top of the fuel tank . Refer to Diagnostic Aids.
  4. Repair the leak in the EVAP system.

Is the action complete?

15 in.H2O

Go to Step 19

--

14

Repair restriction in EVAP Purge Line.

Is action complete?

--

Go to Step 19

--

15

Repair restriction in Fuel Tank Vapor Line.

Is action complete?

--

Go to Step 19

--

16

Replace the EVAP Canister Purge Solenoid Valve. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement in Repair Instructions.

Is the action complete?

--

Go to Step 19

--

17

Replace the EVAP Vent Valve. Refer to Diagnostic Aids. Refer to Evaporative Emission Vent Valve Replacement in Repair Instructions.

Is the action complete?

--

Go to Step 19

--

18

Replace EVAP Canister. Refer to Evaporative Emission Canister Replacement in Repair Instructions.

Is the action complete?

--

Go to Step 19

--

19

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

  1. Turn the ignition ON leaving the engine OFF.
  2. Using the scan tool, command the EVAP Vent Valve ON (Closed).
  3. Pressurize the EVAP system to the first specified value using the Enhanced EVAP Pressure Purge Diagnostic Cart J 41413 (monitor pressure using the gauge on the cart).
  4. Turn the rotary switch on the cart to the HOLD position and observe the EVAP pressure gauge.

Does the pressure decrease to less than the second specified value within 2 minutes?

15 in. H2O

10 in. H2O

Go to Step 2

Go to Step 20

20
  1. Use the scan tool in order to select the DTC and the Clear DTC Information functions.
  2. Perform the Service Bay Test for EVAP.

Is action complete?

--

Go to Step 21

--

21

Does the scan tool display any DTCs in the Freeze Frame and Failure Records?

--

Go to applicable DTC table

System OK