Circuit Description
The ignition relay, also called the main relay, is controlled by the powertrain control module (PCM). The PCM provides a ground for the relay's coil anytime the ignition switch is ON. The ignition relay supplies ignition positive voltage to many engine control systems and components. The following components receive power from the main relay:
| • | The fuel pump relay |
| • | The fuel injectors |
| • | The mass air flow (MAF) sensor |
| • | The EVAP control system solenoids |
| • | The exhaust gas recirculation (EGR) valve |
| • | 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 ignition relay. The resistance across terminal 3 and terminal 5 is 79-95 ohms at 20°C (68°F). The resistance across terminal 1 and terminal 2 is infinite. |
| • | The ignition relay's electrical contacts may be pitted or sticking. Replace the ignition relay if tapping gently on the relay or wiggling the relay causes a change in the relay's operation. |
| • | The temperature may affect the performance of the ignition relay. Check the ignition relay after sitting outside overnight and after running the engine for 30 minutes. |
| • | Check for a faulty electrical connection to the PCM. |
A fault in the ignition relay electrical circuit may cause an intermittent malfunction. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .
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 | Empty | Coil Ground |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
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The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and to store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
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This step will verify whether the PCM is not providing a ground path for the ignition relay circuit. When terminal 2 of the ignition relay is grounded, the ignition relay turns ON.
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This step checks for ignition positive voltage at the PCM. The PCM will not operate the ignition relay if there is no power to terminal C2-20.
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This step checks for an open in the PCM electrical grounds. The PCM will not operate the ignition relay if there are no electrical grounds.
Step | Action | Yes | No | ||||||
|---|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics | |||||||||
Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | ||||||||
2 | Check for an open in the following fuses:
Did you find an open fuse? | Go to Step 13 | Go to Step 3 | ||||||
3 |
Did the ignition relay click when being reinstalled into the relay box? | Go to Step 4 | Go to Step 5 | ||||||
4 |
Does the test lamp illuminate? | Go to Step 14 | Go to Step 7 | ||||||
5 | Probe terminal 3 of the ignition relay, on the relay box side, using a test lamp connected to ground. Does the test lamp illuminate? | Go to Step 6 | Go to Step 7 | ||||||
Does the test lamp illuminate? | Go to Step 14 | Go to Step 8 | |||||||
7 | Repair the open in the ignition positive voltage circuit between the FI fuse and the ignition relay. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 17 | -- | ||||||
8 |
Was a repair necessary? | Go to Step 17 | Go to Step 9 | ||||||
Backprobe PCM electrical connector terminal C2-20 with a test lamp connected to ground. Does the test lamp illuminate? | Go to Step 11 | Go to Step 10 | |||||||
10 | Repair the open in the ignition positive voltage circuit between the IG fuse and the PCM. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 17 | -- | ||||||
Does the test lamp illuminate at each ground terminal? | Go to Step 16 | Go to Step 12 | |||||||
12 | Repair all opens in the PCM ground circuits. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 17 | -- | ||||||
13 | Repair the short to ground in the IG fuse circuit or the FI fuse circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 17 | -- | ||||||
14 |
Did you find and correct a wiring problem? | Go to Step 17 | Go to Step 15 | ||||||
15 | Replace the ignition relay. Did you complete the replacement? | Go to Step 17 | -- | ||||||
16 |
Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 17 | -- | ||||||
17 | Operate the vehicle within the conditions under which the original concern was observed. Does the system operate properly with no DTCs? | System OK | |||||||
