Main Relay Circuit Diagnosis. Pontiac Firefly (Canada) 1999

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1999 🢒 Firefly (Canada) 🢒 Engine 🢒 Engine Controls - 1.3L 🢒 Main Relay Circuit Diagnosis

Refer to

The powertrain control module (PCM) controls the main relay. The PCM provides a ground for the relay's coil anytime the ignition switch is ON. The main relay supplies ignition positive voltage to many engine control systems and to many components. The following components receive power from the main relay:

•	The fuel pump relay

•	The fuel injectors

•	The EVAP control system solenoids

•	The idle air control (IAC) valve

•	The powertrain control module (PCM)

Diagnostic Aids

Check for any of the following conditions:

•	Check the resistance of the main relay. The resistance across terminal 1 and across terminal 2 is 79-95 ohms at 20°C (68°F). The resistance across terminal 3 and across terminal 4 is infinite.

•	The main relays electrical contacts may be pitted or sticking. Replace the main relay if tapping gently on the relay or wiggling the relay causes a change in the relay's operation.

•	Temperature may affect the performance of the main relay. Check the main relay after sitting outside over night and after running the engine for 30 minutes.

•	Check for a faulty electrical connection to the PCM.

A fault in the main relay electrical circuit may result in an intermittent malfunction. Inspect the wiring harness and the components for any of the following conditions:

•	Backed out terminals.

•	Incorrect mating of terminals.

•	Broken electrical connector locks.

•	Incorrectly formed terminals or damaged terminals.

•	Faulty terminal to wire connections.

•	Physical damage to the wiring harness.

•	A broken wire inside the insulation.

•	Corrosion of electrical connections, of splices, or of terminals.

Use the following relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block.

Relay Cavity Identification
Switch Power
Switch Load
Coil Power	Coil Ground

Test Description

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

The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the applicable freeze frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information for later reference.

This step will verify if the PCM is not providing a ground path for the main relay circuit. If terminal 2 of the main relay is grounded, the main relay turns ON.

This step checks for an ignition positive voltage at the PCM. The PCM will not operate the main relay if there is not power to terminal C3-20.

This step checks for an open in the PCM electrical grounds. The PCM will not operate the main relay if there is not an electrical ground.

Step

Action

Value(s)

Yes

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

Check for an open in the following fuses:

•	The IG-COIL fuse

•	The FI fuse

Was an open fuse found?

Go to Step 13

Go to Step 3

Turn ON the ignition, leaving the engine OFF.
Remove and reinstall the main relay several times while listening for a clicking sound from the relay.

Did the main relay click when being installed into the relay box?

Go to Diagnostic Aids

Go to Step 4

Turn OFF the ignition.
Remove the main relay from the relay box.
Turn ON the ignition, leaving the engine OFF.
Probe the relay box side of terminal 4, with a test lamp that is connected to ground. Refer to the Relay Cavity Identification table in Diagnostic Aids.

Does the test lamp illuminate?

Go to Step 5

Go to Step 7

Probe terminal 1 on the relay box side of the main relay with a test lamp that is connected to ground.

Does the test lamp illuminate?

Go to Step 6

Go to Step 7

Turn OFF the ignition.
Probe terminal 2 of the main relay using a test lamp that is connected to battery positive voltage.
Turn ON the ignition, leaving the engine OFF.
Observe the test lamp.

Does the test lamp illuminate?

Go to Step 14

Go to Step 8

Repair the open in the ignition positive voltage circuit between the FI fuse and the main relay. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 16

Check for an open in the main relay control circuit between the main relay and the PCM.
Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 16

Go to Step 9

Backprobe terminal C3-20 of the PCM electrical connector with a test lamp that is connected to ground.

Does the test lamp illuminate?

Go to Step 11

Go to Step 10

Repair the open in the ignition positive voltage circuit between the IG-COIL fuse and the PCM. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 16

Disconnect the PCM electrical connector C1.
Probe the harness side of the PCM ground terminals C1-1, C1-13, and C1-26, with a test lamp that is connected to B+.

Does the test lamp illuminate at each ground terminal?

Go to Step 15

Go to Step 12

Repair all opens in the PCM ground circuits. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 16

Repair the short to ground in the IG-COIL fuse circuit or in the FI fuse circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

Go to Step 16

Replace the main relay. Refer to Main Relay Replacement .

Is the action complete?

Go to Step 16