310S CAN Bus & Scope Waveform Diagnostics Questions
Modern vehicles rely on intricate multiplexed Controller Area Network (CAN) architectures. On the Red Seal 310S Automotive Service Technician Exam, questions testing digital storage oscilloscopes (DSO), serial data bus protocols, and CAN High / Low fault isolation appear frequently.
🚗 310S Automotive Exam Focus: High-Speed CAN (ISO 11898)
- Recessive (Idle) Voltage: Both CAN-H and CAN-L idle at 2.5 Volts.
- Dominant (Active) Voltage: CAN-H rises to 3.5V (+1.0V), while CAN-L drops to 1.5V (-1.0V), creating a 2.0V differential.
- Terminating Resistors: Two 120-ohm resistors wired in parallel at each end of the bus produce a total baseline resistance of 60 Ohms.
1. CAN Bus Fault Isolation Cheat Sheet
| DLC Pins 6 & 14 Resistance Reading | Diagnostic Root Cause | Symptom on Network |
|---|---|---|
| 60 Ohms | Normal. Both 120-ohm terminating resistors are intact. | Normal bus communication. |
| 120 Ohms | One terminating resistor or harness branch is OPEN. | Intermittent communication dropouts, signal reflection. |
| 0 Ohms (Continuity) | Short circuit between CAN-H (Pin 6) and CAN-L (Pin 14). | Total network crash (U-codes across all modules, no crank). |
2. Practice 310S Automotive Questions
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🎧 Watch & Listen: 30 Automotive Service Technician (310S) Practice Questions & Worked Answers
Weighted to the official Red Seal Automotive Service Technician (310S) exam breakdown, read aloud with a 5-second pause before each worked answer and code explanation.
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