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For 1990-2009 cars only

Circuit Description

The exhaust gas recirculation (EGR) valve is vacuum operated. Vacuum for the EGR valve control system is supplied by a belt driven vacuum pump. The EGR valve vacuum control solenoid and the EGR valve vacuum vent solenoid work together to control the position of the EGR valve. The engine control module (ECM) monitors the EGR vacuum sensor signal to determine the amount of vacuum that is applied to the EGR valve. The EGR throttle valve is used to create a restriction in the air intake in order to increase the engine vacuum. When the EGR valve is commanded to open, the EGR valve is commanded open, the EGR throttle valve is commanded to partially close. The increase in engine vacuum aids in the recirculation of the exhaust gases when the EGR valve is open. The ECM uses the mass air flow (MAF) sensor to calculate the amount of exhaust gas that is consumed by the engine. When the EGR valve is opened, the MAF rate will decrease. If the EGR vacuum sensor signal is lower than expected and the MAF rate is higher than expected, it is assumed that the EGR valve is not opening enough due to a vacuum problem and Diagnostic Trouble Code (DTC) P0404 sets.

Conditions for Running the DTC

    • DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0112, P0113, P0116, P0117, P0118, P0405, P0406, P0489, P0490, P0500, P1639, P2142, P2144, and P2145 are not set.
    • The EGR valve vacuum control solenoid has been commanded to more than 70 percent.
    • The PCM is not in the Reduced Engine Power mode.
    • The Engine Run Time parameter is more than 5 seconds.
    • The BARO parameter is more than 72 kPa.
    • The Engine Speed parameter is between 610 - 820 RPM and is steady within 50 RPM for more than 3 seconds.
    • The ECT Sensor parameter is between 60° - 100°C (140°-212°F).
    • The Calculated Fuel Rate parameter is between 3 - 20 mm³.
    • The power take off (PTO) is disabled. (If equipped).
    • The IAT Sensor parameter is more than 0°C (32°F).
    • The APP Indicated Angle parameter is less than 1 percent.
    • The Ignition 1 Signal parameter is between 11-18 volts.
    • The Vehicle Speed Sensor parameter is less than 0.40 kPh (0.25 MPH).
    • All of the above conditions are met for more than 3 seconds.

Conditions for Setting the DTC

    • The ECM detects a lower than expected EGR vacuum sensor signal and a higher than expected MAF rate.
    • The above condition is met for more than 8 seconds.

Action Taken When the DTC Sets

    • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
    • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC

    • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
    • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
    • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
    • Clear the MIL and the DTC with a scan tool.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics or Emission Hose Routing Diagram

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Start the engine.
  2. Using the EGR System Seal Output Control function, command the EGR Solenoid to 100 percent with the scan tool.
  3. Observe the EGR Vacuum Sensor parameter with a scan tool.

Is the vacuum less than the specified value?

35 kPa

Go to Step 3

Go to Step 4

3

  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 4

Go to Intermittent Conditions

4

  1. Disconnect the vacuum line from the EGR vacuum sensor.
  2. Connect a vacuum gage to the vacuum line.
  3. Start the engine.
  4. Allow the engine to reach operating temperature.
  5. Using the EGR System Seal output control function, command the EGR Solenoid to 100 percent with a scan tool.
  6. Observe the vacuum gage.

Does the vacuum measure more than the specified value?

15 in Hg

Go to Step 10

Go to Step 5

5

  1. Turn OFF the engine.
  2. Disconnect the vacuum line from the vacuum pump.
  3. Install a vacuum gage on the vacuum pump with a short piece of vacuum line.
  4. Start the engine.
  5. Observe the vacuum gage.

Does the vacuum measure more than the specified value?

15 in Hg

Go to Step 6

Go to Step 9

6

Test all of the EGR system vacuum lines for leaks and for restrictions.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 7

7

Connect a hand held vacuum pump to the following components to determine if they can hold 15 Hg of vacuum for 30 seconds:

    • The EGR valve vacuum diaphragm
    • The EGR throttle valve vacuum diaphragm

If a problem is found, refer to Exhaust Gas Recirculation Valve Replacement or Air Intake Pipe Replacement .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

8

Connect a hand held vacuum pump to the following components to determine if they can hold 15 Hg of vacuum for 30 seconds:

    • The EGR valve control solenoid
    • The EGR throttle valve control solenoid

If a problem is found, refer to Exhaust Gas Recirculation Valve Solenoid Replacement or Exhaust Gas Recirculation Vacuum Regulator Valve Solenoid Replacement .

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

9

Replace the vacuum pump. Refer to Exhaust Gas Recirculation Valve Vacuum Pump Replacement .

Did you complete the replacement?

--

Go to Step 12

--

10

Replace the EGR vacuum sensor. Refer to Exhaust Gas Recirculation Valve Vacuum Sensor Replacement .

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the EGR vacuum vent solenoid. Refer to Exhaust Gas Recirculation Valve Vent Solenoid Replacement .

Did you complete the replacement?

--

Go to Step 12

--

12

  1. Clear the DTCs with a scan tool.
  2. Turn OFF the ignition for 30 seconds.
  3. Start the engine.
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?

--

Go to Step 2

Go to Go to Step 13

13

Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK