GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The engine control module (ECM) uses the exhaust gas recirculation (EGR) position sensor to determine the position of the EGR valve. The ECM sends a reference voltage through the 5-volt reference circuit to the EGR position sensor. The ECM provides a voltage return path for the sensor through the low reference circuit. A variable voltage signal, based on the EGR valve position, is sent from the sensor to the ECM through the EGR position sensor signal circuit. The ECM compares the actual EGR position with the desired EGR position when the EGR valve is commanded open or closed. If the ECM detects a difference between the learned closed position and the commanded closed position for a calibrated amount of time, DTC P1404 sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1404 Exhaust Gas Recirculation (EGR) Closed Position Performance

Conditions for Running the DTC

    • DTCs P0642 and P0643 are not set.
    • The ignition is ON for more than 0.5 seconds.
    • The ignition voltage is between 11-18 volts.
    • The intake air temperature (IAT) is between 0-150.75°C (32-303.35°F).
    • The engine coolant temperature (ECT) is between 57-99.75°C (134.6-211.6°F).
    • The barometric pressure (BARO) is more than 72 kPa.
    • The power take off (PTO) is not engaged.
    • The EGR has been commanded to more than 35 percent.
    • The current desired EGR position is 0 percent.
    • This diagnostic runs continuously while the above conditions are met.

Conditions for Setting the DTC

    • The actual EGR position is 0.80 volts, 6 percent, more than the learned closed position when the EGR valve is commanded closed, or the EGR learned minimum position is more than 1.25 volts.
    • The above condition is present for more than 5 seconds.

Action Taken When the DTC Sets - California

    • 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.

Action Taken When the DTC Sets - Federal

    • The control module stores the DTC information into memory when the diagnostic runs and fails.
    • The MIL will not illuminate.
    • The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Failure Records.
    • The driver information center (DIC), if equipped, may display a message.

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

Schematic Reference: Engine Control Module Connector End Views or Engine Controls 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

    Important: Attaching the shop exhaust system to the vehicle may cause false exhaust gas recirculation (EGR) DTCs to set.

  1. Turn ON the ignition.
  2. Observe the EGR Position parameter with a scan tool.

Does the EGR Position parameter read more than the specified value?

1.25 V

Go to Step 4

Go to Step 3

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 cycle?

--

Go to Step 4

Go to Intermittent Conditions

4

Is DTC P0403, P0405, or P0406 also set?

--

Go to DTC P0403 or DTC P0405 or DTC P0406

Go to Step 5

5

Test for shorted terminals and poor connections at the exhaust gas recirculation (EGR) valve. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 6

6

  1. Disconnect the EGR valve.
  2. Turn ON the ignition.
  3. Set up the DMM to measure amperage.
  4. Connect a test lamp and a DMM in series between the 5-volt reference circuit of the EGR position sensor and the low reference circuit of the EGR position sensor.
  5. Measure the amperage and note as "current draw".
  6. Remove the DMM and connect the test lamp between the 5-volt reference circuit of the EGR position sensor and the low reference circuit of the EGR position sensor.
  7. Connect a DMM in parallel between the low reference circuit of the EGR position sensor and a good ground.
  8. Measure the voltage and note as "low reference voltage drop".
  9. Divide the "low reference voltage drop" by the "current draw" in order to calculate the resistance in the low reference circuit.

Is the calculated resistance more than the specified value?

5 ohms

Go to Step 7

Go to Step 9

7

Test for shorted terminals and poor connections at the ECM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 8

8

  1. Disconnect the engine control module (ECM).
  2. Repair the high resistance in the low reference circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 11

9

  1. Remove the EGR valve. Refer to Exhaust Gas Recirculation Valve Replacement .
  2. Inspect for debris and damage that will cause the EGR valve to stick.

Did you find and correct the condition?

--

Go to Step 12

Go to Step 10

10

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

Did you complete the replacement?

--

Go to Step 12

--

11

Replace the ECM. Refer to Engine Control Module 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 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