GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Aveo 🢒 Engine 🢒 Engine Controls - 1.2L 🢒 DTC P0400

Circuit Description

The engine control module (ECM) performs a flow test on the exhaust gas recirculation (EGR) system during deceleration. The ECM does this by momentarily commanding the EGR valve to open while monitoring the signal of the manifold absolute pressure (MAP) sensor and the EGR position sensor. If the MAP signal is incorrect for the EGR pintle position, the ECM records the amount of MAP difference that was detected and adjusts a calibrated fail counter towards a calibrated fail threshold level. The number of EGR flow tests required to exceed the fail threshold may vary according to the amount of detected EGR flow error. If the ECM detects an EGR flow error, DTC P0400 sets.

Normally, the ECM will only allow one EGR flow test during an ignition cycle. To aid in verifying a repair, the ECM will allow multiple EGR flow tests following a code clear event.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P0400 Exhaust Gas Recirculation (EGR) Flow Incorrect

Conditions for Running the DTC
    • DTCs P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0131, P0300, P0335, P0336, P0341, and P0342 are not set.
    • The EGR flow test is ran in decel fuel cut-off (DFCO) mode with the following conditions present before deceleration occurs:
       - The engine is operating in closed loop.
       - The ignition 1 voltage is between 11-16 volts.
       - The intake air temperature (IAT) is more than 15°C (59°F).
       - The engine coolant temperature (ECT) is more than 60°C (140°F).
       - The manifold absolute pressure (MAP) is more than 75 kPa (11 psi).
       - The mass airflow (MAF) is between 71-174 mg/tdc.
       - The A/C compressor clutch does not change state during deceleration.
       - The engine speed is between 1,950-2,600 RPM.
       - The EGR is more than 10 percent.
    • The DTC runs once an ignition cycle when the above conditions are met.

Conditions for Setting the DTC

The ECM detects the incorrect amount of intake absolute pressure when compared to the EGR valve position during the EGR flow test.

Action Taken When the DTC Sets
    • The malfunction indicator lamp (MIL) will illuminate after 3 consecutive trips with a fail.
    • The ECM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records buffers.

Conditions for Clearing the MIL/DTC
    • The MIL will turn OFF after 4 consecutive ignition cycles in which the diagnostic runs without a fault.
    • DTCs can be cleared by using the scan tool.
    • Disconnect the ECM battery feed for more than 10 seconds.

Test Description

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

  1. MAP sensor faults must be diagnosed first. A skewed MAP sensor reading could cause this DTC to set.

    2.

  2. An engine mechanical condition may cause the engine to operate poorly, which could cause a low vacuum condition.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View 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
  1. Turn OFF the ignition for 30 seconds.
  2. Start the engine.
  3. Operate the vehicle within the Conditions for Running the DTC.

Did the DTC fail this ignition?

Go to Step 3

Go to Intermittent Conditions

3

Is DTC  P0107 or P0108 also set?

Go to Diagnostic Trouble Code (DTC) List

Go to Step 4

4

Inspect the exhaust gas recirculation (EGR) system for the following conditions:

    • Incorrect EGR valve for engine application.
    • A vacuum leak between the EGR valve and the intake manifold.
    • Signs of external leakage usually indicated by carbon buildup around the mating surfaces of the components or an audible exhaust noise.
    • Restrictions in the passages or EGR valve caused by carbon deposits or casting flash.

Did you find and correct the condition?

Go to Step 9

Go to Step 5

5

Inspect for leaks or restrictions at the manifold absolute pressure (MAP) sensor.

Did you find and correct the condition?

Go to Step 9

Go to Step 6

6

Inspect the exhaust system for the following conditions:

    • Leaks caused by damage to the exhaust components
    • Restrictions that can cause excessive back pressure and low engine vacuum--Restrictions may be caused by aftermarket equipment or damage to the exhaust components.
    • Modification of original equipment manufacture (OEM) parts

Did you find and correct the condition?

Go to Step 9

Go to Step 7

7

  1. Inspect for the following engine mechanical conditions:
    2. • The correct installation of the timing belt
    • Worn piston rings
    • Worn camshaft
    • Other worn or damaged engine components
  2. Refer to Symptoms - Engine Mechanical in Engine Mechanical - 1.2L.

Did you find and correct the condition?

Go to Step 9

Go to Step 8

8

Replace the EGR valve.

Did you complete the replacement?

Go to Step 9

--

9
  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.

Did the DTC fail this ignition?

Go to Step 2

Go to Step 10

10

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK