| Table 1: | Relay Cavity Identification |
Circuit Description
This diagnostic detects that the main relay is stuck ON. The ignition relay, or main relay, is controlled by the powertrain control module (PCM). The PCM provides a ground for the relays coil anytime the ignition switch is ON. The main relay supplies ignition positive voltage to many engine control systems and components. The following components receive power from the relay:
| • | The ignition coils |
| • | The heated oxygen sensors (HO2S) |
| • | The evaporative emission (EVAP) control system solenoids |
| • | The camshaft and crankshaft position sensors |
| • | The powertrain control module (PCM) |
DTC Descriptor
This diagnostic procedure supports the following DTC.
DTC P0688 Engine Controls Ignition Relay Feedback Circuit
Conditions for Running the DTC
| • | The ignition is OFF. |
| • | The battery voltage is at least 10.1 volts. |
| • | DTC P0688 runs continuously with the above condition met. |
Conditions for Setting the DTC
The main relay remains ON even with the ignition OFF for more than 5 seconds.
Action Taken When the DTC Sets
| • | The PCM illuminates the service vehicle soon (SVS) lamp when the diagnostic fails. |
| • | The malfunction indicator lamp (MIL) remains OFF when DTC P0688 sets. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Failure Record buffer. |
Conditions for Clearing the MIL/DTC
| • | The SVS lamp turns OFF after the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Perform the scan tool Clear DTC Information function. |
Diagnostic Aids
| • | Check for any of the following conditions: |
| - | Check the resistance of the relay. The resistance across the coil terminals is 70-90 ohms at 20°C (68°F). The resistance across the switched terminals is infinite. |
| - | The relay electrical contacts may be pitted or sticking. Replace the relay if tapping gently on the relay or wiggling the relay causes a change in the relays operation. |
| - | The performance of the relay may be affected by temperature. Test the relay after sitting outside overnight and after running the engine 30 minutes. |
| - | An intermittent malfunction may be caused by a fault in the relay electrical circuit. 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. |
Front of Vehicle | |
Battery Power Load | Battery Power Coil |
Coil Control | Ignition 1 voltage |
Test Description
The numbers below refer to the step numbers in the diagnostic table.
-
The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and 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.
-
This step determines if a condition exists. The scan tool should not communicate with the PCM with the ignition OFF.
-
This step tests if the main relay is stuck in the ON position.
-
This step determines if there is a condition with the control circuit of the main relay. If the control circuit of the main relay is shorted to ground, the relay will click ON and OFF when you remove and install the relay.
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views | |||
Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | ||
Does the scan tool communicate with the PCM? | Go to Step 3 | Go to Intermittent Conditions | |
Swap the main relay with the cooling fan relay. Does the scan tool communicate with the PCM? | Go to Step 4 | Go to Step 9 | |
Does the relay click when removing and installing the relay? | Go to Step 5 | Go to Step 6 | |
5 |
Did you find and correct the condition? | Go to Step 11 | Go to Step 8 |
6 | Measure the voltage at the ignition 1 voltage of the main relay at the underhood fuse block with a DMM. Does the DMM display a voltage? | Go to Step 7 | Go to Step 9 |
7 | Test the ignition 1 voltage supply circuit of the main relay between the ECM/CAM fuse and the PCM for a short to voltage. Refer to Circuit Testing and Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Step 11 | Go to Step 8 |
8 | Test for shorted terminals and poor connections at the PCM. 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 11 | Go to Step 10 |
9 | Replace the main relay. Did you complete the replacement? | Go to Step 11 | -- |
10 |
Did you complete the replacement? | Go to Step 11 | -- |
11 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 12 |
12 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
