Vehicle Diagnostic Protocol Analyzer
Analyze OBD fault codes and sensor data to pinpoint vehicle diagnostic root causes
What You Can Do
You can rapidly convert raw diagnostic fault codes, sensor readings, and freeze frame data into structured root cause hypotheses using protocol specifications and fault tree analysis. The skill cross-references OBD-II codes against CAN/LIN communication logs and ECU interdependencies to identify whether failures stem from electrical, software calibration, or network-layer issues—reducing diagnostic time from days to hours and eliminating false repair attempts.
Features
Convert P/B/C/U-codes into actionable failure hypotheses with protocol-specific context
Extract and correlate sensor values, timing conditions, and system state at fault occurrence
Rapidly extract J1939, UDS, and OEM specification sections relevant to fault symptoms
Trace multi-layer electrical and software root causes across ECU networks
Analyze bus communication logs to isolate network faults from sensor failures
Cross-check proposed fixes against system interdependencies and calibration requirements
Design reproducible bench and vehicle test procedures for intermittent faults
Example Output
Example 1: P0128 Coolant Thermostat Analysis
Input: P0128 DTC, freeze frame showing coolant temp 65°C at startup, CAN log of ECT sensor variance ±2°C
Output:
- Primary Hypothesis: Stuck-open thermostat or ECT sensor signal degradation
- Secondary Check: Verify cooling fan relay activation timing against specification
- Test Plan: Capture 10-minute ECT ramp curve; compare against OEM calibration table; check CAN message frequency on CANHS_Engine
- Likelihood: 78% thermostat, 18% sensor, 4% wiring
Example 2: U0101 Lost Communication with TCM
Input: U0101 DTC, CAN bus log showing TCM message gaps, freeze frame from highway operation
Output:
- Root Cause Path: Low CAN voltage (9.2V) → TCM transceiver brown-out → Message collision on CAN_IHS
- Electrical Check: Battery voltage drop under 500A load; verify TCM 12V supply and GND resistance <0.1Ω
- Network Analysis: TCM transmit rate increased to 50ms; conflicts with PCM at 25ms. Recommend TCM firmware 2.14+ update
- Validation: Bench test with controlled voltage sag; confirm TCM recovery timing <200ms
What's Included
- SKILL.md: Complete diagnostic protocol framework with use-case guidelines
- OBD Code Reference Matrix: P/B/C/U-code categories mapped to likely root cause paths
- Fault Tree Template: Fillable worksheet for multi-layer electrical/software failure analysis
- CAN/LIN Message Decoder Checklist: Protocol-specific fields and diagnostic extraction steps
- Test Plan Workbook: Standardized format for designing repeatable diagnostic procedures
Who It's For
- Automotive embedded software engineers debugging ECU and multi-network vehicle faults
- Powertrain diagnostic technicians analyzing complex P-codes and sensor interdependencies
- Field service engineers validating repair strategies before customer vehicle deployment
- OEM diagnostic system developers building repeatable test procedures
- Warranty claim analysts documenting root causes for engineering review and compliance
Best For
- OBD-II DTC decoding and freeze frame correlation analysis
- CAN/LIN network fault isolation and message timing analysis
- Multi-ECU diagnostic workflows across powertrain, chassis, and body systems
- Intermittent fault investigation requiring reproducible test design
- Post-update calibration validation and flashing issue troubleshooting
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