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Home >> Mazda >> 2021 >> CX-3 AWD >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Communication Devices >> On-Board Diagnostic - Body Control Module >> DTC B109E-87: Communication Error With Start Stop Unit (BCM) >> Diagnostic Procedure

Diagnostic Procedure

DTC B109E:87 (BCM) DIAGNOSTIC PROCEDURE

Step Inspection Action
1 VERIFY BCM DTCs AGAIN
Yes Go to the next step.
No Go to Step 8.
2 INSPECT START STOP UNIT CONNECTOR CONDITION
  • Switch the ignition off.
  • Disconnect the negative battery cable. (See NEGATIVE BATTERY CABLE DISCONNECTION/CONNECTION .)
  • Disconnect the start stop unit connector.
  • Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection.
  • Is the connector normal?
Yes Go to the next step.
No Repair or replace the connector, then go to Step 7.
3 INSPECT BCM CONNECTOR CONDITION
  • Disconnect the BCM connector.
  • Inspect the connector engagement and connection condition and inspect the terminals for damage, deformation, corrosion, or disconnection.
  • Is the connector normal?
Yes Go to the next step.
No Repair or replace the connector, then go to Step 7.
4 INSPECT WIRING HARNESS BETWEEN START STOP UNIT AND BCM FOR SHORT TO GROUND
  • Verify that the start stop unit and BCM connectors are disconnected.
  • Inspect for continuity between start stop unit terminal 1Q (wiring harness-side) and body ground.
  • Is there continuity?
Yes Refer to the wiring diagram and verify whether or not there is a common connector between start stop unit terminal 1Q and BCM terminal 2J.
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.

Go to Step 7.
No Go to the next step.
5 INSPECT WIRING HARNESS BETWEEN START STOP UNIT AND BCM FOR OPEN CIRCUIT
  • Verify that the start stop unit and BCM connectors are disconnected.
  • Inspect for continuity between start stop unit terminal 1Q (wiring harness-side) and BCM terminal 2J (wiring harness-side).
  • 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 start stop unit terminal 1Q and BCM terminal 2J.
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 7.
6 VERIFY IF MALFUNCTIONING LOCATION IS START STOP UNIT DEPENDING ON REPEATABILITY
Yes Replace the start stop unit, then go to the next step.
(See START STOP UNIT REMOVAL/INSTALLATION .)
No Go to Step 8.
7 VERIFY THAT REPAIRS HAVE BEEN COMPLETED
Yes Repeat the inspection from Step 1.

Go to the next step.
No Go to the next step.
8 VERIFY IF OTHER DTCs DISPLAYED
  • Are any other DTCs displayed?
Yes Repair or replace the malfunctioning part according to the applicable DTC troubleshooting.
(See DTC TABLE (BCM) .)
No DTC troubleshooting completed.