GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2001 🢒 Chevy K Silverado - 4WD 🢒 Engine 🢒 Engine Controls - 8.1L 🢒 DTC P0404

Circuit Description

The powertrain control module (PCM) monitors the exhaust gas recirculation (EGR) valve pintle position input to ensure that the valve responds properly to commands from the PCM. The PCM compares the EGR position sensor with desired EGR position when the valve is commanded open. If the difference between the EGR position sensor and desired EGR position is more than 10 percent, DTC P0404 will set.

Conditions for Running the DTC
    • The ignition voltage is more than 11.7 volts.
    • The commanded EGR position is more than 0 percent.
    • The EGR flow test is not active.
    • The desired EGR does not change more than 20 percent.

Conditions for Setting the DTC
    • The vehicle must be driven.
    • The difference between the desired EGR position and the actual EGR position sensor is more than 10 percent.
    • The condition is present for more than 13 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.

Diagnostic Aids

Inspect for the following conditions:

Excessive deposits on the EGR pintle or seat--Remove the EGR valve, and inspect for deposits that may interfere with the EGR valve pintle extending completely or may cause the pintle to stick.

If the problem is intermittent, refer to Intermittent Conditions .

Test Description

The numbers below refer to the step numbers on the diagnostic table.

  1. This step verifies that the malfunction is present.

    2.

  2. If DTC P0404 will only set under certain conditions, the malfunction may be intermittent. Refer to Diagnostic Aids. If an intermittent wiring problem is not present, test for a faulty connection at the PCM or the EGR valve. If the connections are OK and DTC P0404 continues to set, replace the EGR valve.

  3. When using the scan tool to increment the EGR valve, increment the valve to 100 percent then to 0 percent . Repeat this process to see if the test lamp turns ON then OFF. If the test lamp does not turn OFF when the EGR valve is commanded to 0 percent the EGR solenoid high control circuit is shorted to voltage.

    4.

  4. When using the scan tool to increment the EGR valve, increment the valve to 100 percent then to 0 percent . Repeat this process to see if the test lamp turns ON then OFF. If the test lamp does not turn OFF when the EGR valve is commanded to 0 percent the EGR solenoid high control circuit is shorted to voltage. If the test lamp does not turn ON when the EGR valve is commanded to 100 percent the EGR solenoid high control is open or shorted to ground.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. Command the EGR valve from 0-100 percent with a scan tool.

Does the EGR position sensor remain close to the desired EGR position at all commanded positions?

--

Go to Step 3

Go to Step 4

3

  1. Observe the Freeze Frame/Failure Records data for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text or as close to the Freeze Frame/Failure Records data that you observed.

Does the DTC fail this ignition?

--

Go to Step 4

Go to Diagnostic Aids

4

Observe the EGR position sensor parameter with a scan tool.

Does the scan tool indicate that the EGR position sensor is at the specified value?

0%

Go to Step 7

Go to Step 5

5
  1. Turn OFF the ignition.
  2. Disconnect the EGR valve connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Observe the EGR position sensor parameter with a scan tool.

Does the scan tool indicate that the EGR position sensor is at the specified value?

0%

Go to Step 6

Go to Step 16

6

  1. Turn ON the ignition, with the engine OFF.
  2. Probe the EGR solenoid high control circuit with a test lamp connected to a good ground.
  3. Command the EGR valve between 0-100 percent with a scan tool.

Does the test lamp turn ON and OFF with each command?

--

Go to Step 10

Go to Step 9

7

  1. Turn OFF the ignition.
  2. Disconnect the EGR valve connector.
  3. Turn ON the ignition, with the engine OFF.
  4. Probe the EGR solenoid high control circuit with a test lamp connected to a good ground.
  5. Command the EGR between 0-100 percent with a scan tool.

Does the test lamp turn ON and OFF with each command?

 

Go to Step 8

Go to Step 9

8
  1. Connect a test lamp between the EGR solenoid high control circuit and the EGR solenoid low control circuit.
  2. Command the EGR valve between 0-100 percent with a scan tool.

Does the test lamp turn ON and OFF with each command?

--

Go to Step 20

Go to Step 15

9

Does the test lamp remain illuminated with each command?

--

Go to Step 14

Go to Step 13

10

Measure the voltage from the 5-volt reference circuit of the EGR position sensor to the low reference circuit of the EGR position sensor.

Does the DMM display voltage near the specified value?

5 V

Go to Step 11

Go to Step 12

11

Important: : If the fuse opens, locate and repair a short to ground in the signal circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Connect a fused jumper between the 5-volt reference circuit of the EGR position sensor and the EGR valve position signal circuit of the EGR position sensor.

Does the scan tool indicate that the EGR position sensor is near the specified value?

100%

Go to Step 20

Go to Step 18

12

Measure the voltage from the 5-volt reference circuit of the EGR position sensor to a good ground.

Does the DMM display voltage near the specified value?

5 V

Go to Step 17

Go to Step 19

13

Test the EGR solenoid high control circuit for the following conditions:

    • A short to ground
    • High resistance
    • An open

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

14

Test the EGR solenoid high control circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

15

Test the EGR solenoid low control circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

16

Test the EGR valve position signal circuit for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

17

Test the low reference circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

18

Test the EGR valve position signal circuit for high resistance or a high resistance short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

19

Test the 5-volt reference circuit of the EGR position sensor for one of the following conditions:

    • An open or a short to ground
    • A short to voltage

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 21

20

Inspect for poor connections at the harness connector of the EGR valve. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 22

21

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 24

Go to Step 23

22

Replace the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .

Did you complete the replacement?

--

Go to Step 24

--

23

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 24

--

24
  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 as specified in the supporting text.

Does the DTC run and pass?

--

Go to Step 25

Go to Step 2

25

Observe the stored information, Capture Info with a scan tool.

Does the scan tool display any DTCs that you have not diagnosed?

--

Go to Diagnostic Trouble Code (DTC) List

System OK