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Home >> Mazda >> 2019 >> 6 Signature >> Repair and Diagnosis (Single Page) >> Accessories & Equipment >> Communication Devices >> On-Board Diagnostics - Front Body Control Module (FBCM) >> DTC U0231-68: Communication Error With Humidity Sensor/Auto Light Sensor/Rain Sensor >> Diagnostic Procedure
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Diagnostic Procedure

DTC U0231:68 (FRONT BODY CONTROL MODULE (FBCM)) DIAGNOSTIC PROCEDURE

Step Inspection Action
1 VERIFY FRONT BODY CONTROL MODULE (FBCM) DTCs AGAIN Yes Go to the next step.
No Go to Step 9.
2 INSPECT HUMIDITY SENSOR/AUTO LIGHT SENSOR/RAIN SENSOR CONNECTOR
  • Switch the ignition off.
  • Disconnect the negative battery terminal. (See NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
  • Disconnect the humidity sensor/auto light sensor/rain sensor 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 8.
3 INSPECT FRONT BODY CONTROL MODULE (FBCM) CONNECTOR
  • Disconnect the front body control module (FBCM) 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 8.
4 INSPECT FOR SHORT TO GROUND IN HUMIDITY SENSOR/AUTO LIGHT SENSOR/RAIN SENSOR CIRCUIT
  • Verify that the humidity sensor/auto light sensor/rain sensor and front body control module (FBCM) connectors are disconnected.
  • Inspect for continuity between front body control module (FBCM) terminal 2G (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 humidity sensor/auto light sensor/rain sensor terminal C and front body control module (FBCM) terminal 2G.
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 8.
No Go to the next step.
5 INSPECT FOR SHORT TO POWER SUPPLY IN HUMIDITY SENSOR/AUTO LIGHT SENSOR/RAIN SENSOR CIRCUIT
  • Verify that the humidity sensor/auto light sensor/rain sensor and front body control module (FBCM) connectors are disconnected.
  • Reconnect the negative battery terminal. (See NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
  • Switch the ignition ON (engine off or on).
  • Measure the voltage at the front body control module (FBCM) terminal 2G (wiring harness-side).
  • Is the voltage 0 V?
 Yes Go to the next step.
No Refer to the wiring diagram and verify whether or not there is a common connector between humidity sensor/auto light sensor/rain sensor terminal C and front body control module (FBCM) terminal 2G.
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 power supply.
  • Repair or replace the malfunctioning part.

    If there is no common connector:

  • Repair or replace the wiring harness which has a short to power supply.

Go to Step 8.
6 INSPECT FOR OPEN CIRCUIT IN HUMIDITY SENSOR/AUTO LIGHT SENSOR/RAIN SENSOR CIRCUIT
  • Verify that the humidity sensor/auto light sensor/rain sensor and front body control module (FBCM) connectors are disconnected.
  • Switch the ignition off.
  • Disconnect the negative battery terminal. (See NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
  • Inspect the wiring harness for continuity between humidity sensor/auto light sensor/rain sensor terminal C (wiring harness-side) and front body control module (FBCM) terminal 2G (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 humidity sensor/auto light sensor/rain sensor terminal C and front body control module (FBCM) terminal 2G.
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 8.
7 PERFORM DTC INSPECTION AND VERIFY HUMIDITY SENSOR/AUTO LIGHT SENSOR/RAIN SENSOR MALFUNCTION Yes Replace the humidity sensor/auto light sensor/rain sensor, then go to the next step.
(See RAIN SENSOR REMOVAL/INSTALLATION .)
No Go to Step 9.
8 VERIFY THAT REPAIRS HAVE BEEN COMPLETED Yes Repeat the inspection from Step 1.
Go to the next step.
No Go to the next step.
9 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 (FRONT BODY CONTROL MODULE (FBCM)) .)
No DTC troubleshooting completed.
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