GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Optra 🢒 Engine 🢒 Engine Controls - 1.4L DOHC 🢒 DTC P1478

Circuit Description

Voltage is provided to the exhaust gas recirculation (EGR) solenoid by the ignition 1 voltage circuit through a fuse. Ground is provided to the EGR solenoid on the control circuit by a low side driver within the engine control module (ECM). The ECM energizes the solenoid which allows vacuum to pass to the EGR valve. The ECM monitors the voltage on the control circuit of the EGR valve to determine if a failure is present. If ECM detects the voltage on the control circuit of the EGR solenoid is low while the valve is not commanded while the solenoid is being commanded, this DTC sets.

DTC Descriptor

This diagnostic procedure supports the following DTC:

DTC P1478 Exhaust Gas Recirculation (EGR) Solenoid Control Circuit Open

Conditions for Setting the DTC

The ECM detects an open on the control circuit of the EGR solenoid.

Test Description

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

  1. A click should be heard or felt when the valve operates. Ensure that both the ON and the OFF states are commanded. Repeat the commands as necessary.

    2.

  2. This step tests if the EGR solenoid ignition 1 voltage circuit has a fault. A fault in the main relay, fuse, or underhood bussed electrical center (UBEC) can cause multiply DTC's to set and a no start condition.

    3.

  3. This step verifies that the ECM is providing ground to the EGR solenoid.

    4.

  4. This step tests if the EGR solenoid control circuit is grounded.

Step

Action

Yes

No

Schematic Reference: Engine Controls Schematics

Connect End View Reference: 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 ON the ignition, with the engine OFF.
  2. With the scan tool, command the EGR solenoid ON and OFF.

Do you hear or feel a click from the EGR solenoid when the valve is commanded ON and OFF?

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.

Did the DTC fail this ignition?

Go to Step 4

Go to Intermittent Conditions

4

  1. Disconnect the EGR solenoid electrical connector.
  2. Probe the ignition 1 voltage circuit of the EGR solenoid with a test lamp connected to a good ground.

Does the test lamp illuminate?

Go to Step 5

Go to Step 11

5

  1. Connect a test lamp between the control circuit of the EGR solenoid and the ignition 1 voltage circuit of the EGR solenoid.
  2. With a scan tool, command the EGR solenoid ON and OFF.

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

Go to Step 9

Go to Step 6

6

Does the test lamp remain illuminated with each command?

Go to Step 8

Go to Step 7

7

Test the control circuit of the EGR solenoid 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 14

Go to Step 10

8

Test the control circuit of the EGR solenoid for a short to ground. Refer to Testing for Short to Ground and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 14

Go to Step 10

9

Test for an intermittent and for a poor connection at the EGR solenoid . 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 14

Go to Step 12

10

Test for an intermittent and for a poor connection 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 14

Go to Step 13

11
  1. Repair the ignition 1 voltage circuit of the EGR solenoid for one of the following conditions:
    2. • An open
    • A short to ground
    • High resistance
  2. Replace the fuse as necessary. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 14

--

12

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

Did you complete the replacement?

Go to Step 14

--

13

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

Go to Step 14

--

14
  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 15

15

Are there any DTCs that have not been diagnosed?

Go to Diagnostic Trouble Code (DTC) List

System OK