Evaporative Emission Control System Diagnosis. Chevrolet Corsica 1996

For 1990-2009 cars

Refer to

#### EVAP and EGR Controls

Engine Controls Components
Exhaust Gas Recirculation (EGR) System
Oxygen Sensors
Engine Data Sensors
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
for wiring view.

### Results of Incorrect Operation

Poor idle, stalling and poor driveability can be caused by the following items:

• | Inoperative EVAP canister purge valve.

• | Damaged EVAP canister.

• | Hoses split, cracked and, or not connected to the proper tubes.

Evidence of fuel loss or fuel vapor odor can be caused by the following items:

• | Liquid fuel leaking from fuel lines, or fuel pump.

• | Cracked or damaged EVAP canister.

• | Disconnected, mis-routed, kinked, deteriorated or damaged vapor hoses, or control hoses.

If the EVAP canister purge valve is always open, the canister can purge to the intake manifold at all times. This can allow extra fuel during warm-up, which can cause a too rich operation.

If the EVAP canister purge valve is always closed, the canister can become over-loaded, resulting in fuel odor.

### Diagnosis

The EVAP canister purge valve operation is covered in Evaporative Emission (EVAP) Canister Purge Valve Check and also in DTC's P0441 and P1441 . The EVAP purge vacuum switch is diagnosed by DTC's P0441 and DTC P1441.

A open or shorted circuit in the purge valve can also be diagnosed in PCM Outputs .

### Visual Check of the EVAP Canister

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

### Circuit Description

Canister purge is controlled by a purge valve that allows idle purge and ported vacuum to purge the canister when energized. The Powertrain Control Module (PCM) supplies a ground to energize the valve (purge ON). The purge valve control by the PCM is pulse width modulated (turned ON and OFF several times a second). The duty cycle (pulse width) is determined by Closed Loop feed back from the Oxygen Sensor (O2S). The duty cycle will freeze if the engine has idled longer than 10 seconds and continue incrementing when throttle position rises above 1.5%. The duty cycle is calculated by the PCM and the output commanded when the following conditions have been met:

• | Engine run time after start is more than 120 seconds if coolant temperature less than 56°C (133°F).

• | Engine run time after start is more than 30 seconds if coolant temperature is greater than 56°C (133°F).

• | Engine has not idled longer than 10 seconds.

### Diagnostic Aids

Make a visual check of vacuum hose(s). Check throttle body for possible cracked, broken, or plugged vacuum block. Check the engine for a possible mechanical problem that may cause a low vacuum condition.

The scan tool may be utilized to determine if the purge valve is operating by viewing the EVAP Vacuum Switch parameter. When purge is commanded, and the engine is off idle (approx. 1500 RPM), the EVAP Vacuum Switch should display OFF (purge present). After the engine is returned to idle (no ported vacuum) the EVAP Vacuum Switch will display ON (no purge present).

### Test Description

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

1. Checks if the purge valve is opened or closed. The purge valve is normally de-energized in this step, so it should be closed.

2. Completes functional check by commanding purge valve ON. This should normally energize the purge valve opening the valve which should allow the vacuum to drop (purge ON).

3. Checks to determine if purge valve was open due to electrical circuit problem or defective purge valve.

#### Evaporative Emission (EVAP) Canister Purge Valve 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

2

1. Turn the ignition switch ON, with the engine OFF. (Do not the crank engine before following the steps below):
2. Disconnect the throttle body to EVAP emission canister purge valve vacuum hose from EVAP canister purge valve.
3. Apply the specified of vacuum to the EVAP canister purge valve.

Does the EVAP canister purge valve hold vacuum?

10 Hg (34 kPa)

Go to Step 3

Go to Step 6

3

1. Install a scan tool.
2. Using Misc Tests, command the EVAP canister purge valve ON with the scan tool.

Does the applied vacuum drop?

--

Go to Step 4

Go to Step 5

4

1. Install a vacuum gage to hose that was previously disconnected from the EVAP canister purge valve.
2. Start the engine.
3. Raise engine speed to specified value.
4. Momentarily snap open the throttle and let the throttle return to idle.

Did the vacuum gage value read about the specified value?

2500 RPM 10 Hg (34 kPa)

System OK

Go to Diagnostic Aids

5

1. Disconnect the EVAP canister purge valve electrical connector.
2. Connect a test light between the harness terminals.
3. Using Misc Tests, command the EVAP canister purge valve ON with the scan tool.

Does the test light illuminate when the purge valve is commanded ON?

--

Go to Step 11

Go to Step 7

6

1. Disconnect the EVAP canister purge valve electrical connector.
2. Apply the specified amount of vacuum to the EVAP canister purge valve.

Does the EVAP canister purge valve hold vacuum?

10 Hg (34 kPa)

Go to Step 9

Go to Step 11

7 | Probe each harness terminal with a test light to ground. Did the test light illuminate on one or both terminal? | -- | Go to Step 8 | Go to Step 13
8 | Did the test light illuminate on both terminals? | -- | Go to Step 12 | Go to Step 9
9 | Check for an open or short in the EVAP driver circuit and repair as necessary. Was a repair necessary? | -- | Go to Step 14 | Go to Step 10
10 | Replace PCM. Is action complete? | -- | Go to Step 14 | --
11 | Replace the EVAP canister purge valve. Is action complete? | -- | Go to Step 14 | --
12 | Repair short to voltage in the EVAP driver circuit. Is action complete? | -- | Go to Step 14 | --
13 | Repair open in the ignition feed circuit. Is action complete? | -- | Go to Step 14 | --
14 | Operate the vehicle under the conditions the original symptom was noted. Does the vehicle now operate normally? | -- | System OK | Refer to Diagnostic Aids