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For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 1997 🢒 Firefly (Canada) 🢒 DTC 🢒 DTC P0443 EVAP System Incorrect Purge Flow

Schematic Reference: Engine Controls Schematics

Circuit Description

An evaporative emission control system is used to prevent the emission of fuel vapor. The fuel vapor generated in the fuel tank while driving or idling the engine, passes through the fuel tank pressure control valve and enters the EVAP canister where the charcoal absorbs and stores fuel vapors. The EVAP canister purge valve is a powertrain control module (PCM) operated vacuum solenoid that controls the purging of the fuel vapors stored in the EVAP canister. The EVAP canister purge valve is mounted on the intake manifold next to the EVAP canister surge tank. The EVAP canister purge solenoid valve is turned ON by the PCM under the following conditions:

    • The engine coolant temperature is more than a specified value.
    • Engine RPM is more than a specified value.

Conditions for Running the DTC
    • Engine coolant temperature between 70°C (158°F) and 110°C (230°F)
    • Intake air temperature between -10°C (14°F) and 50°C (122°F)
    • Barometric pressure greater than 75 kPa
    • Fuel tank level is between 25 and 75%.
    • At idle in closed loop

Conditions for Setting the DTC
    • Engine speed change between purge OFF and ON (duty greater than 50%) during idle mode.
    • Conditions present for 20 seconds.

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) will illuminate after two consecutive ignition cycles in which the diagnostic runs with the fault active.
    • The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.

Conditions for Clearing the MIL/DTC
    • The MIL will turn OFF after three consecutive drive cycles without a fault present.
    • A History DTC will clear after 40 consecutive warm-up cycles without a fault.
    • The DTCs can be cleared by using a scan tool or by disconnecting the PCM battery feed.

Diagnostic Aids

Check for any of the following conditions:

    • A cracked or punctured EVAP canister
    • A damaged or disconnected source vacuum line, EVAP purge line, vent hose or fuel tank vapor line
    • A plugged, restricted, leaking or damaged EVAP Canister Surge Tank
    • A poor connection at the PCM -- Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
    • A damaged wiring harness -- Inspect the wiring harness to the EVAP canister purge valve for an intermittent open or short circuitry.

If a DTC P0443 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.

If any wiring repairs need to be made, refer to Repair Procedures in Electrical Diagnosis.

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

    2.

  2. Determine if the fault is present. Review Freeze Frame data to determine when the DTC set. Always record this information.

    3.

  3. Indicates whether the malfunction is in the control circuitry or in the EVAP canister.

    4.

  4. This step checks the components that supply manifold vacuum to the EVAP canister purge valve. A plugged or leaking EVAP canister surge tank could prevent vacuum from reaching the EVAP canister purge valve.

    5.

  5. An EVAP canister purge valve test. Duty cycle control is disabled by the PCM until the engine has reached a normal operating temperature of at least 80°C (176°F) and there is no RPM input. Output controls can be found on the Tech 2 scan tool under Special Functions.

    6.

  6. An EVAP canister purge valve control circuit test -- The EVAP canister purge valve duty cycle control is disabled by the PCM until the engine has reached a normal operating temperature of at least 80°C (176°F) and there is no RPM input. Output controls can be found on the Tech 2 scan tool under Special Functions.

    7.

  7. This step checks the EVAP canister.

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 ON the ignition.
  2. Use the scan tool clear information function.
  3. Operate the vehicle within the Freeze Frame conditions as noted.

Is a DTC P0443 set?

--

Go to Step 3

Refer to Diagnostic Aids

3

Important: The EVAP canister purge system does not perform purging (vacuum will not be detected at the purge hose) unless the engine is sufficiently warmed up and the H02S 1 is fully active. When the purge hose is disconnected in step 5, air can be drawn into the purge line. As a result, the PCM may detect a change in the purge gas concentration and sometimes will stop purging. This is a normal action and may be the cause of a failure to detect vacuum in Step 6. If no vacuum is felt in Step 6, continued testing of the EVAP system may be necessary to avoid replacement of good parts.

  1. Start the engine.
  2. Disconnect the purge hose from the EVAP canister.
  3. Place your finger against the end of the disconnected hose and check that vacuum is NOT felt when the engine is cool and running at idle speed.
  4. Connect the purge hose to the EVAP canister and bring the engine up to normal operating temperature.
  5. Disconnect the purge hose from EVAP canister.
  6. Place your finger against the end of the disconnected hose and check that vacuum is felt when the engine is running at idle speed.

Were both checks satisfactory?

--

Go to Step 9

Go to Step 4

4

With the engine running at normal operating temperature, check for any of the following conditions at the EVAP canister purge valve:

    • No manifold vacuum from the intake manifold vacuum port
    • Leaking or damaged hoses
    • Clogged or restricted hoses or passages
    • Faulty EVAP Canister Surge Tank

Repair any problems found in the checks above.

Was a repair necessary?

--

Go to Step 15

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the EVAP canister purge valve electrical connector.
  3. Using a DMM, measure the resistance of the EVAP canister purge valve.

Is the resistance within the specified value?

33-40 ohms at 20°C (68°F)

Go to Step 6

Go to Step 13

6

  1. Disconnect the EVAP canister purge valve vacuum hoses from the intake manifold and from the EVAP canister.
  2. Reconnect the EVAP canister purge valve electrical connector.
  3. Turn ON the ignition.
  4. Blow air into the EVAP canister purge valve vacuum hose that was disconnected from the EVAP canister. Air should not pass through the EVAP canister purge valve and exit from the intake manifold hose.
  5. Using a scan too, command with the EVAP canister purge valve ON and adjust the duty cycle to 100%.
  6. Blow air into the EVAP canister purge valve vacuum hose that was disconnected from the EVAP canister. Air should pass through the EVAP canister purge valve and exit from the intake manifold hose.

Did the EVAP canister purge valve pass both inspections?

--

Go to Step 9

Go to Step 7

7
  1. Turn ON the ignition.
  2. With the test light connected to ground, probe the WHT/BLU wire at the EVAP canister purge valve electrical connector.

Is the test light ON?

--

Go to Step 8

Go to Step 12

8

  1. With a test light connected to B+, probe the EVAP canister purge valve control circuit RED/GRN wire at the EVAP canister purge valve electrical connector.
  2. Using the scan tool, command the EVAP canister purge valve ON. Adjust the duty cycle from 0 to 100% while monitoring the test light.

Does the test light flash and then come on steadily when you reach 100% duty cycle?

--

Go to Step 13

Go to Step 10

9

  1. Disconnect the hoses from the EVAP canister.
  2. Using a small length of hose connected to the tank pipe at the EVAP canister, blow into the EVAP canister. Air should escape from both the purge tube and the air tube.

Did the EVAP canister pass the inspection?

--

Go to Diagnostic Aids

Go to Step 11

10
  1. Check for an open or a short in the EVAP canister purge valve control circuit.
  2. Repair as necessary.

Was a repair necessary?

--

Go to Step 15

Go to Step 14

11

Replace the EVAP canister. Refer to Evaporative Emission Canister Replacement .

Is the action complete?

--

Go to Step 15

--

12

Check for an open in the WHT/BLU wire. Repair as necessary.

Is the action complete?

--

Go to Step 15

--

13

Replace the EVAP canister purge valve. Refer to Evaporative Emission Canister Purge Solenoid Valve Replacement .

Is the action complete?

--

Go to Step 15

--

14

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 15

--

15

After the repairs, use the scan tool clear information function and road test the vehicle within the Freeze Frame conditions that set the DTC. Check for DTCS. Review the scan tool data and if no DTCS are stores, the repair is complete.

Are any DTCs displayed on the scan tool?

--

Go to the Applicable DTC Table

System OK