Evaporative Emission Control System Diagnosis EVAP System Check
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.
Diagnostic Aids
Check for the following conditions:
| • | A poor connection at the Control Module. Inspect the harness connectors for the following conditions: |
| - | Backed out terminals |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connections. |
| • | A damaged harness. Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Vacuum display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the display will indicate the location of the fault. |
| • | An incorrect purge or vacuum source line routing. Verify that the source vacuum and purge lines to the EVAP canister purge valve are not switched. |
Refer to Carbon Particle Removal from EVAP System before starting repairs.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 |
Important: Before clearing DTCs use the scan tool Capture Info to record freeze frame and failure records for reference, as data will be lost when Clear Info function is used. Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check for 2.2L or Powertrain On Board Diagnostic (OBD) System Check for 4.3L | |
2 | Are any DTCs set? | -- | Go to the Applicable DTC Table | |
3 |
Is the Fuel Tank Pressure at the specified value? | 0 in. H2O (±1 in. H2O) | ||
4 |
Important: Before continuing with the diagnosis, zero the EVAP Pressure and Vacuum gauges on J 41413 Enhanced EVAP Pressure Purge Diagnostic Cart (refer to tool operating instructions).
Is Fuel Tank Pressure at the specified value? | 5 in. H2O (± 2 in. H2 O) | ||
5 | Observe Fuel Tank Pressure on the scan tool while commanding the vent solenoid OFF (Open). Does Fuel Tank Pressure decrease to the specified value within 5 seconds? | 0 in. H20 (±1 in. H2O) | Go to DTC P0446 Evaporative Emission (EVAP) Vent System Performance for 2.2L or DTC P0446 Evaporative Emission (EVAP) Vent System Performance for 4.3L | |
6 |
Is Fuel Tank Pressure increasing? | 1500 RPM | Go to DTC P1441 Evaporative Emission (EVAP) System Flow During Non-Purge for 2.2L or DTC P1441 Evaporative Emission (EVAP) System Flow During Non-Purge for 4.3L | |
7 |
Is Fuel Tank Pressure increasing? | 1500 RPM | System OK If a driveability symptom exists, refer to Driveability Symptoms | Go to DTC P0440 Evaporative Emission (EVAP) System for 2.2L or DTC P0440 Evaporative Emission (EVAP) System for 4.3L |
Evaporative Emission Control System Diagnosis Fuel Tank Pressure Sensor
Circuit Description
The fuel tank vapor pressure sensor is used in order to detect a vacuum decay or an excessive vacuum during the EVAP diagnostic routine. The sensor responds to the changes in the fuel tank pressure or vacuum. The signal voltage to the Control Module 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 Vacuum display on the scan tool has an auto zero feature which occurs at each ignition cycle and is corrected according to the barometric pressure. Because of this, the Fuel Tank Vacuum may not accurately reflect the actual output of the sensor or the conditions within the fuel tank.
The Fuel Tank Vapor Pressure Sensor Diagnosis Table is intended to isolate and diagnose the electrical problems in the sensor wiring or the sensor.
Diagnostic Aids
Check for the following conditions:
| • | Inspect the Control Module harness connectors for the following conditions: |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed |
| - | Damaged terminals |
| • | Inspect the wiring harness for damage. If the harness appears to be OK, observe the Fuel Tank Vacuum display on the scan tool while moving the connectors and the wiring harnesses related to the sensor. A change in the display will indicate the location of the fault. |
Refer to Carbon Particle Removal from EVAP System before starting repairs.
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
The Powertrain OBD System Check prompts the technician to do some basic checks and store the Freeze Frame Data and Failure Records in the scan tool if applicable. This creates an electronic copy of the freeze frame data taken when the fault occurred that can be referred to later.
-
A normal fuel tank pressure sensor voltage output with no pressure or vacuum on the fuel system should be between 1.3 V and 1.7 V.
-
Reprogram the replacement Control Module. Refer to the latest Techline information for programming procedures.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check for 2.2L or Powertrain On Board Diagnostic (OBD) System Check for 4.3L | ||
2 |
Is voltage near the specified value? | 5 V | ||
3 | Check the 5 volt reference circuit for a poor terminal connection at the Control Module. Was a problem found? | -- | ||
4 | Check for an open 5 volt reference circuit to the fuel tank pressure sensor harness connector. Was a problem found? | -- | ||
Is voltage between the specified values? | 1.3 V-1.7 V | |||
6 |
Was a repair necessary? | -- | ||
7 |
Was a repair necessary? | -- | ||
8 |
Was a repair necessary? | -- | ||
9 | Check for an open in the sensor ground circuit. Was a problem found? | -- | ||
10 |
Was a repair necessary? | -- | ||
11 | Replace the faulty harness connector terminals as necessary. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
12 | Locate and repair open or short circuit in wiring harness as necessary. Refer to Wiring Repairs . Is the action complete? | -- | -- | |
13 | Replace the fuel tank pressure sensor. Refer to Diagnostic Aids. Refer to Fuel Tank Pressure Sensor Replacement . Is the action complete? | -- | -- | |
Replace the Control Module. Refer to Powertrain Control Module Replacement/Programming for 2.2L or VCM Replacement/Programming for 4.3L. | -- | -- |
Evaporative Emission Control System Diagnosis Visual Check of EVAP Canister
If cracked or damaged, replace canister. Refer to EVAP Canister Replacement .
Evaporative Emission Control System Diagnosis Overview
| • | Use the Evaporative System Check to diagnose the EVAP system. Refer to Evaporative Emission Control System Diagnosis . |
| • | For the EVAP canister purge valve operation, refer to EVAP Control System (General Description) . |
| For the EVAP canister purge valve diagnosis, refer to the appropriate DTC table. |
| • | For the EVAP vent solenoid operation, refer to EVAP Control System (General Description) . |
| For the EVAP vent solenoid diagnosis, refer to DTCs P0440, P0446, and P1441. Refer to the appropriate DTC table. |
| • | For the fuel tank pressure sensor operation, refer to EVAP Control System (General Description) . |
| For the fuel tank pressure sensor diagnosis, refer to DTCs P0440, P0446, and P1441. Refer to the appropriated DTC table. |
| • | In order to diagnose an open or shorted circuit in the EVAP canister purge valve and the EVAP vent solenoid, refer to Powertrain Control Module Outputs Diagnosis . |
