Circuit Description
The main relay provides ignition positive voltage to many engine control components anytime the ignition is ON. One side of the coil of the main relay is always grounded. The relay is energized when the ignition switch applies voltage to the other side of the coil. The switch side of the main relay receives powered from the main fuse in the underhood fuse block. When the coil is energized, a magnetic field closes the switch side of the relay, supplying power to the following engine components:
| • | Fuel injectors |
| • | Heated oxygen sensors (HO2S) |
| • | Camshaft position (CMP) sensor |
| • | Evaporative emission (EVAP) purge solenoid |
| • | EVAP vent solenoid |
| • | Engine cooling fan relays |
Diagnostic Aids
| • | Test the condition of the main relay circuits. Measure for 75-95 ohms at 20°C (68°F) continuity across the relay coil, terminal 85 to terminal 86. Measure for infinite resistance across the relay switch, terminal 30 to terminal 87. |
| • | The main relay 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. |
| • | The performance of the main relay may be affected by temperature. Check the main relay after sitting outside overnight and after running the engine 30 minutes. |
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 underhood fuse block.
Main Relay Terminal Identification | |
|---|---|
Load | Ignition 1 Voltage |
Ground | B+ |
Front of Vehicle | |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Diagnostic System Check - Engine Controls Connector End View Reference: Engine Control Module Connector End Views and Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Engine Controls? | Go to Step 2 | |
2 |
Important: This procedure assumes there are no open fuses. Perform any necessary repairs and replace the open fuse before using this procedure.
Did the test lamp illuminate on at least one terminal for both fuses? | Go to Intermittent Conditions | Go to Step 3 |
3 | Did the test lamp illuminate for at least one fuse? | Go to Step 9 | Go to Step 4 |
4 |
Did the test lamp illuminate? | Go to Step 5 | Go to Step 10 |
5 | Connect the test lamp between the ignition 1 voltage circuit of the main relay and ground. Did the test lamp illuminate? | Go to Step 6 | Go to Step 11 |
6 | Connect the test lamp between the ground circuit of the main relay and B+. Did the test lamp illuminate? | Go to Step 7 | Go to Step 12 |
7 | Test for an intermittent and for a poor connections at the main relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct a condition? | Go to Step 13 | Go to Step 8 |
8 | Replace the main relay. Did you complete the replacement? | Go to Step 13 | -- |
9 | Repair the open or poor connection in the load circuit of the main relay between the relay and the applicable fuse. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 13 | -- |
10 | Repair the open or poor connection in the B+ circuit of the main relay. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 13 | -- |
11 | Repair the open or poor connection in the ignition 1 voltage circuit of the main relay. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 13 | -- |
12 | Repair the open or poor connection in the ground circuit of the main relay. Refer to Testing for Intermittent Conditions and Poor Connections and Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 13 | -- |
13 | Operate the vehicle within the conditions under which the original concern was noted. Does the system operate properly with no DTCs? | System OK | |
