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Makes 🢒 GMC_Truck 🢒 1996 🢒 GMC C Pickup - 2WD 🢒 Engine 🢒 Engine Controls - 5.0L, 5.7L, and 7.4L 🢒 Evaporative Emission Control System Diagnosis

Evaporative Emission Control System Diagnosis Results of Incorrect Operation

    • Poor idle, stalling and poor driveability can be caused by:
       - Damaged canister
       - Hoses split, cracked, or not connected to the proper tubes
    • Evidence of fuel loss or fuel vapor odor can be caused by:
       - Liquid fuel leaking from the fuel lines
       - Cracked or damaged EVAP canister
       - Disconnected, misrouted, kinked, deteriorated or damaged EVAP pipe or canister hoses
       - Air cleaner or air cleaner gasket improperly seated

Evaporative Emission Control System Diagnosis Inspection of EVAP Canister

    • Replace the EVAP canister if cracked or damaged.
    • Replace the EVAP canister if fuel is leaking from the bottom and then check the operation of the total system.

Evaporative Emission Control System Diagnosis System Check


Object Number: 33299 Size: MF
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

Circuit Description

12 volts is applied to the ignition feed circuit at terminal A when the ignition key is turned ON. As the engine coolant temperature rises during engine operation (less than 45°C (113°F)) or when Short Term Fuel Trim count is greater than 122, the control module will then ground the EVAP canister purge control circuit at terminal B. The purge solenoid will then open the EVAP canister to purge the fuel to the intake manifold for normal combustion when needed.

Test Description

Number(s) below refer to the step numbers on the Diagnostic Table

  1. Checks to see if a vacuum source is present, along with certain conditions before the purge solenoid is commanded ON. Also shows a change of vacuum as the purge solenoid is being cycled

    2.

  2. Checks for power to the solenoid, the ground circuit, the connections at the purge solenoid and the solenoid itself.

    3.

  3. Checks for an open or grounded ignition feed circuit.

    4.

  4. Checks for an open EVAP canister purge control circuit or faulty control module.

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to the Powertrain On Board Diagnostic (OBD) System Check

2
  1. Set the parking brake and block the drive wheels.
  2. Make sure the engine coolant temperature is greater than the specified value.
  3. Start the engine and run at idle.
  4. Check the vacuum source.
  5. If no vacuum, repair the cause of no vacuum. If OK, continue with this table.
  6. Disconnect the purge outlet hose from the solenoid and connect a vacuum gauge.
  7. Connect a scan tool and select the EVAP purge solenoid control.
  8. Raise the engine speed to the specified value.
  9. Command the EVAP purge solenoid ON using the scan tool.

Is vacuum present when the solenoid is energized?

45°C (113°F)

2000 RPM

Go to Step 6

Go to Step 3

3
  1. Disconnect the purge solenoid harness connector.
  2. Connect a test light between the EVAP canister purge control signal and the ignition feed circuit.
  3. Command the EVAP purge solenoid ON using the scan tool.

Is the test light ON?

--

Go to Step 7

Go to Step 4

4
  1. Connect the test light to an alternate ground.
  2. Probe the ignition feed circuit.

Is the test light ON?

--

Go to Step 5

Go to Step 8

5
  1. Connect the test light to B+.
  2. Probe the EVAP canister purge control circuit at the control module.
  3. Command the EVAP purge solenoid ON with the scan tool.

Is the test light ON?

--

Go to Step 9

Go to Step 10

6

Check the purge line to the EVAP canister and repair if necessary. If the purge line is OK, then no problem is found.

Is the action complete?

--

Go to Step 13

--

7
  1. Check for faulty connections at the EVAP purge solenoid.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 13

Go to Step 11

8

Repair the open in the ignition feed circuit.

Is the action complete?

--

Go to Step 13

--

9

Repair the open in the EVAP canister purge control circuit to the EVAP purge solenoid.

Is the action complete?

--

Go to Step 13

--

10
  1. Check for any faulty connections at the control module.
  2. If a problem is found, repair as necessary.

Was a problem found?

--

Go to Step 13

Go to Step 12

11

Replace the EVAP purge solenoid. Refer to the EVAP Canister Purge Solenoid .

Is the action complete?

--

Go to Step 13

--

12

Replace the control module. Refer to VCM Replacement/Programming .

Is the action complete?

--

Go to Step 13

--

13
  1. Turn the ignition ON, engine OFF.
  2. Using a scan tool, command the component ON and OFF.

Does the component operate properly?

--

System OK

Go to Step 2