C1C5A91 Fault Code Technical Analysis Document

Section 3: Fault Depth Definition

DTC: C1C5A91 (MPC Initial Calibration Out of Range)
This fault code is a diagnostic Trouble Code for the vehicle control system, used specifically to identify communication or initialization calibration anomalies between the Multi-Function Video Controller (MPC) and the entire vehicle Electronic Control Unit (ECU). In the vehicle powertrain or multimedia control architecture, the MPC system bears critical signal processing and control tasks. “Initial Calibration” refers to the baseline parameter self-learning process that the control unit performs on internal sensors, actuators, and communication modules after power-up. C1C5A91 triggering means that during the logical judgment phase, the ECU discovered that the initialization data or feedback signals uploaded by MPC deviated from the preset safe threshold range. This usually implies that the system failed to establish correct physical positions or electrical baselines during the startup self-check stage, causing the control unit to enter a protective fault state (System Function Failure).

Section 3: Common Fault Symptoms

Based on fault occurrence conditions and system failure logic, owners and maintenance technicians may observe the following specific dashboard feedback or driving experience abnormalities during diagnosis:

• System Function Loss: All output functions related to the Multi-Function Video Controller stop working, including but not limited to no signal on display, audio interruption, or unresponsive control commands.
• Startup Self-Check Failure: After ignition is turned on, the instrument panel may light up relevant fault indicator lights (Check Engine Light or dedicated system lights), accompanied by specific warning prompts.
• Communication Link Interruption: ECU and MPC cannot complete the handshake protocol, resulting in loss or errors of status monitoring data for related subsystems.

Section 3: Core Fault Cause Analysis

Dissecting from a diagnostic logic level, the generation of C1C5A91 is generally attributed to potential problems in the following three dimensions:

• Hardware Component: Internal components of the Multi-Function Video Controller (MPC) body aging, integrated chip damage or storage unit anomalies causing inaccurate output of initialization parameters.
• Wiring & Connectors: Signal transmission harnesses connecting ECU and MPC exist short circuits, open circuits or excessive contact resistance phenomena, or related connector pins oxidized, causing abnormal signal voltage, thereby judged as calibration out of range.
• Controller Logic Operations: Control algorithm inside ECU makes wrong judgment when processing MPC feedback data, or software version is incompatible with current hardware calibration parameters, leading system to unable correctly parse initial calibration results.

Section 3: Technical Monitoring and Trigger Logic

To accurately determine this fault code, diagnostic strategy follows the following specific monitoring logic and timing conditions:

• Monitoring Target: ECU collects real-time Initial Calibration Result data stream reported by MPC, focusing on analyzing whether its numerical value is within allowed logical boundaries.
• Numerical Range Judgment: System internally sets strict Calibration Parameter Valid Interval. Once ECU receives feedback values exceeding preset tolerance range, it triggers abnormal flags. Although specific voltage threshold depends on underlying calibration files, judgment principle is "Out of Range".
• Specific Conditions: Fault logic is monitored only when vehicle start switch is placed in ON Position (Ignition Switch in ON Position). Only during ECU execution of initialization program after ignition power is established does this condition trigger to officially light DTC and store C1C5A91 code.