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Home >> Mazda >> 2022 >> MX-5 Miata RF Club >> Repair and Diagnosis >> Accessories & Equipment >> Communication Devices >> On-Board Diagnostic - Electric Supply Unit (ESU) >> DTC U0422-86: Error Signal Received From BCM [Electrical Supply Unit (ESU)] >> Diagnostic Procedure

Diagnostic Procedure

DTC U0422:86 (ELECTRICAL SUPPLY UNIT) DIAGNOSTIC PROCEDURE

Step Inspection Action
1 VERIFY BCM DTCs 
 Yes Repair or replace the malfunctioning part according to the applicable DTC troubleshooting.
(See DTC TABLE [BCM] .)
No Go to the next step.
2 INSPECT BCM CONNECTOR CONDITION 
  • Switch the ignition off.
  • Disconnect the negative battery terminal. (See NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
  • 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.
3 INSPECT ELECTRICAL SUPPLY UNIT (ESU) CONNECTOR CONDITION 
  • Disconnect the electrical supply unit (ESU) 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 LIN COMMUNICATION CIRCUIT BETWEEN BCM AND ELECTRICAL SUPPLY UNIT (ESU) FOR SHORT TO GROUND 
  • Verify that the BCM and electrical supply unit (ESU) connectors are disconnected.
  • Inspect for continuity between BCM terminal 2Y (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 BCM terminal 2Y and electrical supply unit (ESU) terminal 2I.
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 LIN COMMUNICATION CIRCUIT BETWEEN BCM AND ELECTRICAL SUPPLY UNIT (ESU) FOR SHORT TO POWER SUPPLY 
  • Verify that the BCM and electrical supply unit (ESU) connectors are disconnected.
  • Connect the negative battery terminal. (See NEGATIVE BATTERY TERMINAL DISCONNECTION/CONNECTION .)
  • Switch the ignition ON (engine off or on).
  • Measure the voltage at the BCM terminal 2Y (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 BCM terminal 2Y and electrical supply unit (ESU) terminal 2I.
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 7.
6 VERIFY IF MALFUNCTIONING LOCATION IS BCM DEPENDING ON REPEATABILITY 
 Yes Replace the BCM, then go to the next step.
(See BODY CONTROL MODULE (BCM) 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 [ELECTRICAL SUPPLY UNIT (ESU)] .)
No DTC troubleshooting completed.
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