GM Service Manual Online
For 1990-2009 cars only

Evaporative Emission Control System Diagnosis EVAP System Check

Refer to

EVAP and EGR Controls


Object Number: 25332  Size: FS
Engine Controls Components
Exhaust Gas Recirculation (EGR) System
Oxygen Sensors
Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
.

Circuit Description

The evaporative emission system is checked by applying vacuum to the EVAP system and monitoring for a vacuum decay. The PCM monitors the vacuum level through the fuel tank vapor pressure sensor signal. At an appropriate time, the EVAP canister purge valve and the EVAP vent solenoid are turned 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 is turned OFF, sealing the system. A leak is detected by monitoring for a decrease in vacuum level over a given time period, when all other variables remain constant. A leak, blockage or faulty component in the system will cause a DTC to be set.

Diagnostic Aids

Check for the following conditions:

    • Poor electrical connection at PCM. Inspect harness electrical connectors for the following conditions:
       - Backed out terminals
       - Improper mating
       - Broken locks
       - Improperly formed
       - Damaged terminals
       - Poor terminal to wire connection
    • Damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Vacuum Pressure display on the scan tool while moving electrical connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the malfunction.
    • Incorrect purge or vacuum source line routing. Verify that the source vacuum and purge lines to the EVAP canister purge solenoid valve are not switched.

Evaporative Emission System Check

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to

Powertrain On Board Diagnostic (OBD) System Check J car 2,4L

Powertrain On Board Diagnostic (OBD) System Check J car 2.2L

2

Are any DTCs set?

--

Go to DTC Diagnostic Tables first

Go to Step 3

3

  1. Turn the ignition switch ON.
  2. Remove the fuel cap.
  3. Observe Fuel Tank Vacuum Pressure on the scan tool.

Is Fuel Tank Vacuum Pressure at the specified value?

0 in H2O (1 in H2O)

Go to Step 4

Go to

Evaporative Emission Control System Diagnosis J car 2.4L

Evaporative Emission Control System Diagnosis J car 2.2L

4

Important:: Before continuing with diagnosis, zero the EVAP Pressure and Vacuum gages on EVAP pressure/purge cart J 41413 (refer to tool operating instructions).

  1. Reinstall the fuel cap.
  2. Using the scan tool, command the EVAP vent solenoid ON (Closed).
  3. Connect the EVAP pressure/purge cart J 41413 to the EVAP service port.
  4. Pressurize the EVAP system to the first specified value using the EVAP pressure/purge cart J 41413 (monitor pressure using gage on cart).
  5. Observe Fuel Tank Vacuum Pressure on the scan tool.

Is Fuel Tank Vacuum Pressure at the second specified value?

5 in H2O

5 in H2O (± 2 in H2O)

Go to Step 5

Go to

Evaporative Emission Control System Diagnosis J car 2.4L

Evaporative Emission Control System Diagnosis J car 2.

5

Observe EVAP System Pressure on the EVAP pressure/purge cart J 41413 while commanding the vent solenoid OFF (Open).

Does EVAP System Pressure decrease to the specified value within 5 seconds?

0 in. H2O

Go to Step 6

Go to

DTC P0446 Evaporative Emission (EVAP) Vent System Performance J car 2.4L

DTC P0446 Evaporative Emission (EVAP) Vent System Performance J car 2.2L

6

  1. Start the engine.
  2. Remove the fuel cap.
  3. Using a scan tool, command the EVAP vent solenoid ON (closed) and the EVAP canister purge valve OFF (0%).
  4. Replace the fuel cap.
  5. Raise the engine RPMs to the specified value.
  6. Monitor Fuel Tank Vacuum Pressure on the scan tool for at least 5 seconds.

Is Fuel Tank Vacuum Pressure decreasing?

1500 RPM

Go to

DTC P1441 Evaporative Emission (EVAP) System Flow During Non-Purge J car 2.4L

DTC P1441 Evaporative Emission (EVAP) System Flow During Non-Purge J car 2.2L

Go to Step 7

7

  1. Using a scan tool, command the EVAP vent solenoid ON (closed) and the EVAP canister purge valve ON (100%).
  2. Raise the engine RPM's to the specified value.
  3. Monitor Fuel Tank Vacuum Pressure on the scan tool for at least 5 seconds.

Is Fuel Tank Vacuum Pressure decreasing?

1500 RPM

System OK. If a driveability symptom exists, refer to Symptoms

Go to

DTC P0440 Evaporative Emission (EVAP) System J car 2.4L

DTC P0440 Evaporative Emission (EVAP) System J car 2.2L

Evaporative Emission Control System Diagnosis Fuel Tank Pressure Sensor

Refer to

Engine Data Sensors


Object Number: 25331  Size: FS
Engine Controls Components
Information Sensors
EVAP and EGR Controls
Fuel Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
.

Circuit Description

The fuel tank pressure sensor is used to detect vacuum decay and excess vacuum during the EVAP diagnostic routine. The sensor responds to changes in fuel tank pressure or vacuum. The signal voltage to the PCM varies from a minimum of about 0.2 volts with pressure in the fuel tank to above 4 volts with a high vacuum in the fuel tank.

The Fuel Tank Pressure display on the scan tool has an auto zero feature which occurs at each ignition cycle and is corrected according to barometric pressure. Because of this,Fuel Tank Pressure may not accurately reflect the actual output of the sensor or conditions within the fuel tank.

The Fuel Tank Pressure Sensor Diagnosis is intended to isolate and diagnose electrical problems with the sensor wiring or the sensor.

Diagnostic Aids

Check for the following conditions:

    • Inspect the PCM harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and for poor terminal to wire connections.
    • Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Pressure display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the display will indicate the location of the fault.

Test Description

  1. The Powertrain OBD System Check prompts the technician to use the Capture Info . selection on the scan tool. This creates an electronic copy of the freeze frame data taken when the fault occurred. The information is then stored in the scan tool for later reference.

  2. Refer to Section 6C for fuel tank removal.

  3. A normal fuel tank vapor pressure sensor voltage output with no pressure or vacuum on the fuel system should be between 1.3 V and 1.7 V.

  4. Replacement PCM's must be reprogrammed. Refer to the latest Techline information for programming procedures.

Fuel Tank Vapor Pressure Sensor Diagnosis

Step

Action

Value(s)

Yes

No

1

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

--

Go to Step 2

Go to

Powertrain On Board Diagnostic (OBD) System Check 2.4L

Powertrain On Board Diagnostic (OBD) System Check 2.2L

2

  1. Disconnect the fuel tank vapor pressure sensor electrical connector.
  2. Using a DVM, measure voltage between the 5 volt reference A circuit and the sensor ground circuit at the fuel tank vapor pressure sensor harness connector.

Is voltage near the specified value?

5V

Go to Step 5

Go to Step 3

3

Check the 5 volt reference A circuit for a poor terminal connection at the PCM.

Was a problem found?

--

Go to Step 11

Go to Step 4

4

Check for an open 5 volt reference A circuit to the fuel tank vapor pressure sensor harness connector.

Was a problem found?

--

Go to Step 10

Go to Step 8

5

  1. Remove the fuel cap.
  2. Using the correct test adapter from connector test adapter kit J 35616-A, connect a jumper between terminal A at the fuel tank vapor pressure sensor pigtail and terminal A at the harness connector (PCM side).
  3. Connect a second jumper between terminal C at the fuel tank vapor pressure sensor pigtail and terminal C at the harness connector (PCM side).
  4. Using a DVM, measure voltage at terminal B at the fuel tank vapor pressure sensor pigtail.

Is voltage between the specified values?

1.3-1.7V

Go to Step 6

Go to Step 13

6

Check the fuel tank vapor pressure sensor signal circuit for a poor terminal connection at the PCM and repair as necessary.

Was a repair necessary?

--

Go to Step 11

Go to Step 7

7

Check the fuel tank pressure signal circuit between the fuel tank vapor pressure sensor connector and the PCM for an open, short to ground, or short to voltage and repair as necessary.

Was a repair necessary?

--

Go to Step 12

Go to Step 14

8

Check the sensor ground circuit for a poor terminal connection at the PCM and repair as necessary.

Was a repair necessary?

--

Go to Step 11

Go to Step 9

9

Check for an open in the sensor ground circuit.

Was a problem found?

--

Go to Step 12

Go to Step 14

10

Check for a poor circuit terminal connection at the fuel tank vapor pressure sensor connector and repair as necessary.

Was a repair necessary?

--

Go to Step 11

Go to Step 13

11

Replace the faulty harness connector terminals as necessary.

Is the action complete?

--

Go to

Evaporative Emission Control System Diagnosis 2.4L

Evaporative Emission Control System Diagnosis 2.2L

--

12

Locate and repair open/short circuit in wiring harness as necessary.

Is the action complete?

--

Go to

Evaporative Emission Control System Diagnosis 2.4L

Evaporative Emission Control System Diagnosis 2.2L

--

13

Replace the fuel tank vapor pressure sensor.

Is the action complete?

--

Go to

Evaporative Emission Control System Diagnosis 2.4L

Evaporative Emission Control System Diagnosis 2.2L

--

14

Replace the PCM.

Is the action complete?

--

Go to

Evaporative Emission Control System Diagnosis 2.4L

Evaporative Emission Control System Diagnosis 2.2L

--

Evaporative Emission Control System Diagnosis Visual Check of EVAP Canister

Visual Check of the EVAP Canister

If cracked or damaged, replace canister. Refer to EVAP Canister Replacement .

Evaporative Emission Control System Diagnosis Overview

Diagnosis

    • The EVAP system can be diagnosed by using EVAP Control System Diagnosis 2.4L or EVAP Control System Diagnosis 2.2L.
    • EVAP canister purge valve operation is covered in this section and diagnosed in DTCs P0440, P0446, and P1441.
    • EVAP vent solenoid operation is covered in this section and diagnosed in DTC's P0440, P0442, and P0446.
    • Fuel tank vapor pressure sensor operation is covered in this section and diagnosed in DTCs P0440, P0442, P0446, P1441 and Evaporative Emission System Check.
    • A open or shorted circuit in the EVAP canister purge valve and EVAP vent solenoid can also be diagnosed in Powertrain Control Module Outputs Diagnosis 2.4L Powertrain Control Module Outputs Diagnosis 2.2L.