GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2004 🢒 Regal 🢒 Engine 🢒 Engine Controls - 3.8L (L36 and L67) 🢒 DTC P0404

Circuit Description

The exhaust gas recirculation (EGR) valve position sensor is monitored by the powertrain control module (PCM). The 5-volt reference circuit, low reference circuit and the EGR valve position signal circuit are used by the PCM to determine the EGR valve position. The PCM compares the EGR Position Sensor parameter with the Desired EGR Position parameter when the valve is commanded open or closed. If the PCM detects a calibrated difference between the EGR Position Sensor parameter and Desired EGR Position parameter for a calibrated amount of time when the EGR valve is commanded open, DTC P0404 sets.

Conditions for Running the DTC
    •  The Ignition 1 Signal parameter is more than 11 volts.
    • The EGR command will be disabled if the startup ECT is less than 5°C (41°F), and will not enable until the ECT is more than 75°C (167°F).
    • The EGR valve is commanded to open.
    • The EGR flow test is not running.

Conditions for Setting the DTC
    • The difference between the EGR Position Sensor parameter and the Desired EGR Position parameter is more than 15 percent.
    •  The above condition is met for more than 20 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 excessive deposits on the EGR pintle or seat. Inspect for deposits that may interfere with the EGR valve pintle extending completely or cause the pintle to stick.
    • If the condition is intermittent, refer to Intermittent Conditions .

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Controls Connector End Views or Powertrain Control Module Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

--

Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Is DTC P0403 or P0405 also set?

--

Go to Diagnostic Trouble Code (DTC) List

Go to Step 3

3

  1. Turn ON the ignition, with the engine OFF.
  2. Command the exhaust gas recirculation (EGR) valve from 0 percent to 100 percent with a scan tool.

Does the EGR Position Sensor parameter remain within 15 percent of the desired EGR Position parameter when commanded with a scan tool?

--

Go to Step 4

Go to Step 5

4
  1. Observe the Freeze Frame/Failure Records for this DTC.
  2. Turn OFF the ignition for 30 seconds.
  3. 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 5

Go to Diagnostic Aids

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

Is the EGR position sensor parameter less than the specified value?

1%

Go to Step 6

Go to Step 11

6

Connect a test lamp between the 5-volt reference circuit of the EGR valve and the low reference circuit of the EGR valve

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 8

7
  1. Connect a 3-amp fused jumper wire between the 5-volt reference circuit of the EGR valve and the EGR valve position signal circuit.
  2. Observe the EGR Position Sensor parameter on the scan tool.

Is the EGR Position Sensor parameter more than the specified value?

99%

Go to Step 9

Go to Step 13

8

Connect a test lamp between the 5-volt reference circuit of the EGR valve and a good ground.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 14

9

Important: If the scan tool output control function times out, re-command the EGR valve to 100 percent before the next electrical measurement is taken.

  1. Command the EGR valve to 100 percent with a scan tool.
  2. Measure the voltage from the EGR high control circuit to a good ground. Note the results in volts as "supply voltage".
  3. Connect a jumper wire between the EGR low control circuit and the corresponding terminal on the EGR valve.
  4. Connect a DMM between the EGR high control circuit and the corresponding terminal on the EGR valve.
  5. Measure the note and current draw in amps.
  6. Remove the DMM from the EGR high control circuit.
  7. Connect a jumper wire between the EGR high control circuit and the corresponding terminal on the EGR valve.
  8. Connect a DMM in parallel between the EGR high control circuit and a good ground.
  9. Measure the voltage drop in volts and note as "load voltage drop".
  10. Subtract the load voltage drop from the supply voltage then divide the answer by the current draw. The result is the amount of resistance in the EGR high control circuit.

Is the calculated resistance more than the specified value?

3 ohms

Go to Step 15

Go to Step 10

10

Important: If the scan tool output control function times out, re-command the EGR valve to 100 percent before the next electrical measurement is taken.

  1. Connect a DMM in parallel between the EGR low control circuit and a good ground.
  2. Measure the voltage drop in volts and not as "low control voltage drop".
  3. Divide the low control voltage drop by the current draw. The result is the amount of resistance in the low control circuit.

Is the calculated resistance more than the specified value?

3 ohms

Go to Step 16

Go to Step 17

11

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 21

Go to Step 18

12

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

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

13

Test the EGR valve position signal circuit for the following conditions:

    • An open
    • A short to ground
    • High resistance

Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

14

Test the 5-volt reference circuit of the EGR valve for an open or for high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

15

Test the high control circuit of the EGR valve for resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

16

Test the low control circuit of the EGR valve for resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 21

Go to Step 18

17

Test for an intermittent and for a poor connection at 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 21

Go to Step 19

18

Test for an intermittent and for a poor connection at the powertrain control module (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 21

Go to Step 20

19

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

Did you complete the replacement?

--

Go to Step 21

--

20

Replace the PCM. Refer to Powertrain Control Module Replacement .

Did you complete the replacement?

--

Go to Step 21

--

21
  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 Step 22

22

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