C1203 - FAULT CODE - OBD2

C1203 LEXUS, TOYOTA: ECM COMMUNICATION CIRCUIT MALFUNCTION

The ECM (Engine Control Module) monitors the engine operation and has to be sure the engine is working optimally. It monitors most of the sensors related to the engine control for the appropriate management of the car’s air-fuel mixture. It also monitors the regulation of the emission control system.

The ECM regulates fundamental systems of the car such as the air-fuel ratio, ignition timing, variable valve timing, and idle speed. In all this process, the different sensors play their fundamental role. For example, the MAF Sensor (Mass Air Flow Sensor), the Oxygen Sensors (O2), the CKP Sensor (Crankshaft Position Sensor), among others.

The ECM communication circuit is used to send TRAC and VSC data from the slip control ECU to the ECM, and the Hybrid Control System information from the ECM to the slip control ECU via the CAN communication system. Identification data that is provided from other Engine Control Units is stored when it is sent from the factory and is used as default values. If this circuit has a wrong operation, for example, the actual values do not match the set values, the fault code C1203 OBDII will be set.

• The Check Engine light turns on.
• ABS warning light illuminated.

The C1203 OBD2 diagnostic code C1203 is stored due to these reasons:

• Engine Control Module cables may be damaged.
• The ECM communication circuit may have poor electrical connections.
• The Motor Control Module may be in poor condition.

To solve the DTC C1203 OBDII code, try this:

• See Technical Service Bulletins.
• Check all the cables and connectors that are related to the ECM, and check them for common damage. If you discover burns or wear on these components, make repairs.
• Measure the ECM communication circuit voltages and compare these values with those indicated on the vehicle's information source. If you discover out-of-range voltages, check for bad connections. Repair if necessary.
• In some cases, the C1203 code is stored by an incorrect ECM installation. If initialization is performed and learning occurs with an incorrect ECU installed, the operations and functions will differ from those stored by the manufacturer. For this reason, make sure that the learning is carried out correctly.