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Home >> Mazda >> 2021 >> MX-5 Miata Club, Automatic Trans >> Repair and Diagnosis >> Engine Performance >> System >> On-Board Diagnostic - Engine Control (2 Of 3) >> DTC P0685-00: Main Relay Control Circuit Open >> Diagnostic Procedure

Diagnostic Procedure

DTC P0685:00 (PCM, SKYACTIV-G 2.0) DIAGNOSTIC PROCEDURE

STEP INSPECTION RESULTS ACTION
1 RECORD VEHICLE STATUS AT TIME OF DTC DETECTION TO UTILIZE WITH REPEATABILITY VERIFICATION
NOTE:
  • Recording can be facilitated using the screen capture function of the PC.
  • Record the FREEZE FRAME DATA/snapshot data on the repair order.
- Go to the next step.
2 VERIFY RELATED REPAIR INFORMATION AVAILABILITY
  • Verify related Service Bulletins and/or on-line repair information availability.
  • Is any related repair information available?
Yes Perform repair or diagnosis according to the available repair information.
  • If the vehicle is not repaired, go to the next step.
No Go to the next step.
3 INSPECT MAIN RELAY
Yes Replace the main relay, then go to Step 9.
No Go to the next step.
4 INSPECT MAIN RELAY POWER SUPPLY CIRCUIT FOR SHORT TO GROUND OR OPEN CIRCUIT
  • Main relay is removed.
  • Measure the voltage at the main relay terminal D (wiring harness-side).
  • Is the voltage B+?
Yes Go to the next step.
No Inspect the MAIN 200 A fuse and ENG.MAIN 40 A fuse.
  • If the fuse is blown:
    • Refer to the wiring diagram and verify whether or not there is a common connector between MAIN 200 A fuse and main relay terminal D.

    If there is a common connector:

  • Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for a short to ground.
  • Repair or replace the malfunctioning part.

    If there is no common connector:

  • Repair or replace the wiring harness which has a short to ground.
  • Replace the malfunctioning fuse.
  • If the fuse is damaged:
    • Replace the malfunctioning fuse.
  • If all fuses are normal:
    • Refer to the wiring diagram and verify whether or not there is a common connector between battery positive terminal and main relay terminal D.

    If there is a common connector:

  • Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for an open circuit.
  • Repair or replace the malfunctioning part.

    If there is no common connector:

  • Repair or replace the wiring harness which has an open circuit.

Go to Step 9.
5 INSPECT PCM POWER SUPPLY CIRCUIT FOR SHORT TO GROUND
  • Main relay is removed.
  • Inspect for continuity between main relay terminal C (wiring harness-side) and body ground.
  • Is there continuity?
Yes Disconnect the PCM connector and inspect the wiring harness for short to ground.
  • If the short to ground circuit could be detected in the wiring harness:
    • Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals:
  • Main relay terminal C-PCM terminal 2BO
  • Main relay terminal C-PCM terminal 2BR

    If there is a common connector:

  • Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for a short to ground.
  • Repair or replace the malfunctioning part.

    If there is no common connector:

  • Repair or replace the wiring harness which has a short to ground.
  • If the short to ground circuit could not be detected in the wiring harness:

Go to Step 9.
No Go to the next step.
6 INSPECT PCM CONNECTOR CONDITION
  • Disconnect the PCM connector.
  • Inspect for poor connection (such as damaged/pulled-out pins, corrosion).
  • Is there any malfunction?
Yes Repair or replace the connector and/or terminals, then go to Step 9.
No Go to the next step.
7 INSPECT PCM GROUND CIRCUIT FOR OPEN CIRCUIT
  • Main relay is removed.
  • Verify that the PCM connector is disconnected.
  • Inspect for continuity between the following harnesses:
    • PCM terminal 2BQ (wiring harness-side)-Body ground
    • PCM terminal 2BT (wiring harness-side)-Body ground
  • Is there continuity?
Yes Go to the next step.
No Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals:
  • PCM terminal 2BQ (wiring harness-side)- Body ground
  • PCM terminal 2BT (wiring harness-side)- Body ground

    If there is a common connector:

  • Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for an open circuit.
  • Repair or replace the malfunctioning part. If there is no common connector:
  • Inspect for the following:
    • Open circuit between PCM and body ground
    • Loose or lifting ground point
  • Repair or replace the malfunctioning part.

Go to Step 9.
8 INSPECT PCM POWER SUPPLY CIRCUIT FOR OPEN CIRCUIT
  • Main relay is removed.
  • Verify that the PCM connector is disconnected.
  • Inspect for continuity between the following terminals (wiring harness-side):
    • Main relay terminal C-PCM terminal 2BO
    • Main relay terminal C-PCM terminal 2BR
  • Is there continuity?
Yes Go to the next step.
No Refer to the wiring diagram and verify whether or not there is a common connector between the following terminals:
  • Main relay terminal C-PCM terminal 2BO
  • Main relay terminal C-PCM terminal 2BR If there is a common connector:
  • Determine the malfunctioning part by inspecting the common connector and the terminal for corrosion, damage, or pin disconnection, and the common wiring harness for an open circuit.
  • Repair or replace the malfunctioning part. If there is no common connector:
  • Repair or replace the wiring harness which has an open circuit.

Go to the next step.
9 VERIFY DTC TROUBLESHOOTING COMPLETED
Yes Repeat the inspection from Step 1.

Go to the next step.
No Go to the next step.
10 VERIFY AFTER REPAIR PROCEDURE
Yes Go to the applicable DTC inspection.
(See DTC TABLE [PCM (SKYACTIV-G 2.0)] .)
No DTC troubleshooting completed.