Diagnostic Strategy

The communication bus (line) between body control ECU and each of the other ECUs on the system is constantly monitored by the body control ECU to determine if communication is possible. See Fig 1. A DTC will be output ONLY when communication is NOT possible or if a short to voltage or a short to ground is detected. A DTC will be set under any of the following conditions:

1. Body control ECU detects a short to voltage or a short to ground on Green, Violet, Green/Black, Green/White, or Red/Yellow wires. See Fig 1. DTC B1214/14 is set when communication bus is shorted to battery voltage. DTC B1215/15 is set when communication bus is shorted to ground.
2. Body control ECU loses complete communication due to an open circuit condition or connector disconnection. See Fig 1.
   • A DTC would set if connector B4, B5, D19, F14, P21 or T4 is disconnected.
   • A DTC would set if an open circuit condition is present on Green/White wire or Violet wire. These are single circuits for communication with theft deterrent ECU and power seat ECU (with driving position memory).
   • A DTC would set if an open circuit condition is present on the following pairs of wires; Green wire and Green/Black wire, Green wire and Red/Yellow wire, or Green/Black wire and Red/Yellow wire. See Fig 1. These are loop circuits for communication between body control ECU and both door control ECUs.

Fig 1: Multiplex Communication System Schematic

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