P0688

DTC P0688

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 Computers and Control Systems Ignition Relay Feedback Circuit

CONDITIONS FOR RUNNING THE DTC
- The ignition is OFF.
- DTC P0688 runs continuously with the above condition met.

CONDITIONS FOR SETTING THE DTC
The main relay remains ON even with the ignition OFF

ACTION TAKEN WHEN THE DTC SETS
- The PCM illuminates the malfunction indicator lamp (MIL) the first time the diagnostic fails.
- The PCM records the operating conditions at the time the diagnostic fails. This information is stored in the Freeze Frame buffer.

CONDITIONS FOR CLEARING THE MIL/DTC
- The MIL turns OFF after 3 consecutively passing trips without a fault present.
- 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. 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.

TEST DESCRIPTION

Steps 1-12:

The numbers below refer to the step numbers in the diagnostic table.
1. The Diagnostic System Check-Computers and Control Systems 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.
2. This step determines if a condition exists. The scan tool should not communicate with the PCM with the ignition OFF.
3. This step tests if the main relay is stuck in the ON position.
4. 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.