GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2005 🢒 Spark 🢒 Engine 🢒 Engine Controls - 0.8L 🢒 Main Relay Circuit Diagnosis

Circuit Description

When the ignition is turned ON or to the START position, the main relay is energized. The main relay then supplies voltage to the engine fuse block fuse EF25 and EF26. The electronic ignition (EI) system ignition coil is supplied voltage through the engine fuse block fuse EF26. The fuel injectors are supplied voltage through the engine fuse block fuse EF25.

Diagnostic Aids
    • An intermittent problem may be caused by a poor connection, rubbed through wire insulation, or a broken wire inside the insulation.
    • A fault main relay will cause a no start condition. There will be no voltage supplied to the EI system ignition coil or the fuel injectors. Without voltage supplied to these components, they will not operate.

Step

Action

Values

Yes

No

1
  1. Turn the ignition OFF.
  2. Disconnect the engine fuse block fuse EF26.
  3. Turn the ignition ON.
  4. With a test light connected to the ground, probe the fuse terminals nearest the main relay for fuse EF19.

Is the light ON at both terminals?

--

System OK

Go to Step 2

2

Is the light on at only one terminal?

--

Go to Step 3

Go to Step 4

3

Repair the open in the wiring between the main relay connector terminal 30 and the fuse EF19 as needed.

Is the repair complete?

--

System OK

--

4
  1. Turn the ignition OFF.
  2. Remove the main relay.
  3. Turn the ignition ON.
  4. With a test light connected to the ground, probe the main relay terminals 85 and 30.

Is the light ON at both terminals?

--

Go to Step 8

Go to Step 5

5
  1. Turn the ignition OFF.
  2. Inspect the engine fuse block fuse EF19.

Is one or both fuse blown?

--

Go to Step 6

Go to Step 7

6
  1. Repair the short circuit between terminal 87 of the main relay and heated oxygen sensor.
  2. Replace fuse EF19.

Is the repair complete?

--

System OK

--

7

Repair the open circuit between terminal 30 of the main relay and fuse EF19.

Is the repair complete?

--

System OK

Go to Step 8

8
  1. Turn the ignition OFF.
  2. Measure the resistance between following terminals:
    3. • Terminal 86 of the main relay and ground
    • Terminal 87 of the main relay and ground

Is the resistance within the specified value?

0 ohms

Go to Step 10

Go to Step 9

9

Repair the open circuit.

Is the repair complete?

--

System OK

--

10

Replace the main relay.

Is the repair complete?

--

System OK

--