CAN Protocol Question & Answers July 15, 2022 By WatElectronics The Controller Area Network (CAN) Bus Protocol is one of the most reliable and widely used communication protocols in embedded systems, automotive electronics, industrial automation, medical devices, aerospace, and robotics. Developed by Bosch in the 1980s, CAN enables multiple Electronic Control Units (ECUs) to exchange information over a two-wire differential communication bus without requiring a central controller. One of the key strengths of the CAN protocol is its high reliability, fault tolerance, priority-based message arbitration, and built-in error detection mechanisms. Unlike traditional serial communication methods, CAN allows several nodes to communicate simultaneously while ensuring that high-priority messages are transmitted first without collisions. This MCQ series is designed for: Electronics and Communication Engineering (ECE) students Electrical Engineering (EEE) students Embedded Systems engineers Automotive Electronics engineers GATE, PSU, and competitive exam aspirants Interview preparation Automotive software developers Each question includes: Four multiple-choice options Correct answer Detailed explanation to reinforce the concept 1). What is the primary purpose of the CAN Bus protocol? Internet communication Communication between microcontrollers and devices without a host computer Wireless communication Satellite communication None Hint 2). CAN Bus was originally developed for which industry?with each other? Aerospace Automotive Telecommunications Consumer Electronics None Hint 3). Which company developed the CAN protocol? Intel Texas Instruments Bosch Motorola None Hint 4). CAN is best classified as which type of communication protocol? Parallel communication Differential serial communication Optical communication Microwave communication None Hint 5). Which layer of the OSI model does the CAN protocol mainly define? Physical and Data Link layers Session layer Presentation layer Application layer None Hint 6). Which communication topology is used in CAN Bus? Ring Star Bus Mesh None Hint 7). Which communication method does CAN primarily use? Master-Slave Peer-to-Peer Multi-Master Client-Server Point-to-Point None Hint 8). How many wires are normally used in a standard CAN Bus? One Two Four Eight None Hint 9). Which signaling technique provides CAN with high noise immunity? Amplitude Modulation Differential Signaling Frequency Modulation PWM None Hint 10). What does ECU stand for in automotive CAN networks? Electronic Control Unit Electrical Computing Unit Embedded Communication Unit External Control Utility None Hint 11). Which ISO standard defines Classical CAN?occurring at the ____ layer? ISO 9001 ISO 11898 ISO 26262 ISO 27001 None Hint 12) What is the maximum data rate of Classical High-Speed CAN?? 125 kbps 250 kbps 500 kbps 1 Mbps None Hint 13). Which feature allows multiple CAN nodes to transmit without data collision? CRC Bit Stuffing Arbitration Synchronization None Hint 14). Which identifier has the highest priority during CAN arbitration? Highest numerical value Lowest numerical value Longest identifier Random identifier None Hint 15). CAN Bus communication is considered which type of transmission? Half-duplex broadcast Full-duplex point-to-point Simplex Optical duplex None Hint 16). Which component converts logic-level CAN signals into differential bus signals?speed CAN? UART CAN Transceiver ADC Multiplexer None Hint 17). Which device generates CAN frames and manages message transmission? CAN Controller CAN Cable Oscilloscope Voltage Regulator None Hint 18). What is one major advantage of CAN over point-to-point wiring in vehicles? Increased wiring complexity B. Reduced wiring and lower vehicle weight Higher power consumption Dedicated cable for every ECU None Hint 19). Which of the following is NOT a typical application of CAN Bus? Engine Management Systems Industrial Automation Airbag Control Systems Wi-Fi Routers None Hint 20). Why is CAN considered a highly reliable communication protocol? It uses optical fiber. It includes arbitration, error detection, retransmission, and fault confinement mechanisms. It operates only at very low speeds. It requires a central master controller. None Hint CAN Protocol MCQs for Interviews 21). Which two wires form the physical communication medium in a High-Speed CAN network? TX and RX SDA and SCL CAN_H and CAN_L MOSI and MISO None Hint 22). Why are CAN_H and CAN_L usually twisted together in a cable? To increase data rate To reduce electromagnetic interference (EMI) To reduce cable cost To increase voltage None Hint 23). During the recessive state, what is the approximate voltage on both CAN_H and CAN_L? CAN_H = 5 V, CAN_L = 0 V CAN_H = 3.3 V, CAN_L = 1.2 V Both approximately 2.5 V Both 0 V None Hint 24). During the dominant state, the voltage on CAN_H typically rises to approximately: 1.5 V 2.5 V 3.5 V 5 V None Hint 25). What is the approximate voltage on CAN_L during a dominant bit? 5 V 3.5 V 2.5 V 1.5 V None Hint 26). What is the primary function of termination resistors in a CAN network? Increase transmission speed Reduce reflections on the communication bus Increase current flow Reduce ECU power consumption None Hint 27). What is the typical resistance value of each CAN bus termination resistor? 10 Ω 47 Ω 120 Ω 1 kΩ None Hint 28). How many termination resistors are normally used in a High-Speed CAN network? One Two Three Four None Hint 29). If one termination resistor is missing, the measured resistance across CAN_H and CAN_L is approximately: 30 Ω 60 Ω 120 Ω 240 Ω None Hint 30). Which bus topology is recommended for High-Speed CAN networks?? Star topology Ring topology Linear bus topology Fully connected mesh None Hint Read more about bus topology. 31). What is the maximum recommended length of branch (stub) connections in a High-Speed CAN network? DLC CRC RTR ACK None Hint 32). Which logic value corresponds to a dominant bit in CAN communication? Logic 0 Logic 1 High impedance Floating state None Hint 33). Which logic value represents a recessive bit? Logic 0 Logic 1 5 V only Undefined state None Hint 34). What happens if one node transmits a dominant bit while another transmits a recessive bit at the same time? A collision destroys both messages. The dominant bit overrides the recessive bit. Both bits are ignored. The bus enters an error state immediately. None Hint 35). Which CAN frame type is used to transmit actual application data? Error Frame Overload Frame Data Frame Suspend Frame None Hint 36). Which CAN frame type is used to request data from another node without carrying a data payload? Error Frame Remote Frame Overload Frame Diagnostic Frame None Hint 37). Which field in a CAN Data Frame determines the message priority during arbitration? CRC Field Data Field Identifier Field ACK Field None Hint 38).How many bits are used in the Standard CAN identifier? 8 bits 11 bits 16 bits 29 bits None Hint 39). How many bits are used in the Extended CAN identifier? 11 bits 16 bits 29 bits 32 bits None Hint 40). What is the primary purpose of the Identifier Field in a CAN message? Store error information Define transmission speed Identify the message and determine its priority Specify the number of nodes on the network None Hint CAN Protocol MCQs for Exams 41). Which bit marks the beginning of every CAN frame?interconnection model? ACK Bit Start of Frame (SOF) CRC Delimiter End of Frame (EOF) None Hint 42). What is the logic level of the Start of Frame (SOF) bit?in harsh environments? Recessive (Logic 1) Dominant (Logic 0) High Impedance Floating None Hint 43). Which field immediately follows the Start of Frame in a Standard CAN Data Frame? CRC Field Arbitration Field ACK Field End of Frame None Hint 44). What is the primary purpose of the Control Field in a CAN frame? Detect transmission errors Indicate the number of data bytes and frame format Acknowledge received frames Synchronize nodes None Hint 45). What does DLC stand for in a CAN Data Frame? Data Link Control Data Length Code Dynamic Logic Circuit Data Line Communication None Hint 46). What is the maximum number of data bytes that can be transmitted in a Classical CAN Data Frame? 4 bytes 8 bytes 16 bytes 64 bytes None Hint 47). If the DLC value is 5 in a Classical CAN frame, how many data bytes are transmitted? 4 bytes 5 bytes 6 bytes 8 bytes None Hint 48). Which field contains the actual application information being transmitted? CRC Field Data Field ACK Field Arbitration Field None Hint 49). What is the primary purpose of the CRC Field? Increase transmission speed Detect transmission errors Identify the transmitting ECU Request retransmission None Hint 50). What does CRC stand for? Central Routing Code Cyclic Redundancy Check Control Register Circuit Communication Routing Control None Hint CAN Protocol MCQs for Quiz 51). Which field follows the CRC Field in a CAN Data Frame? Data Field ACK Field SOF Arbitration Fieldc None Hint 52). What is the purpose of the ACK Slot? Start frame synchronization Confirm that at least one node received the frame correctly Detect bit stuffing errors Identify message priority None Hint 53). If no receiving node acknowledges a transmitted CAN frame, what happens? The transmitter assumes successful delivery. The frame is automatically retransmitted. The network shuts down immediately. The message is permanently discarded. None Hint Read more about CAN Protocol 54). Which field marks the end of a CAN frame? Start of Frame End of Frame (EOF) Arbitration Field Control Field None Hint 55). Why does CAN use bit stuffing? To increase the data rate To maintain synchronization between transmitting and receiving nodes To reduce cable length To encrypt transmitted data None Hint Read more about CAN vs CAN FD. 56). According to CAN bit stuffing rules, after how many consecutive bits of the same polarity is a complementary stuff bit inserted? Three Four Five Eight None Hint 57). What happens if six consecutive identical bits are detected where bit stuffing applies? Normal communication continues. A Bit Stuffing Error is detected. Arbitration restarts. The message priority changes. None Hint 58). Which mechanism allows CAN receivers to synchronize their clocks with the transmitter? CRC Bit Timing Synchronization ACK Slot Arbitration None Hint 59). Which parameter determines the point within a bit period at which the receiver samples the incoming signal? Data Length Code Sample Point Identifier CRC Polynomial None Hint 60). Which statement best describes CAN error detection?priority? CAN detects errors only using CRC. CAN relies solely on acknowledgments. CAN employs multiple error-detection mechanisms, including CRC, bit monitoring, bit stuffing checks, frame checks, and acknowledgment monitoring. CAN cannot detect transmission errors. None Hint 61). Which CAN frame is transmitted immediately after a node detects a communication error? Data Frame Remote Frame Error Frame Overload Frame None Hint 62). What is the primary purpose of an Error Frame? Request data from another ECU Notify all nodes that the current frame is invalid Increase transmission speed Synchronize the network clock None Hint 63). Which CAN frame is used to provide additional processing time before receiving the next frame? Error Frame Overload Frame Data Frame Remote Frame None Hint 64). Which of the following is NOT a standard CAN frame type? Data Frame Remote Frame Error Frame Handshake Frame None Hint 65). Which mechanism prevents a faulty CAN node from continuously disrupting network communication? Encryption Fault Confinement Frequency Hopping Packet Routing None Hint 66). Which two counters are maintained by every CAN controller for fault confinement? Read Counter and Write Counter Timer Counter and Frame Counter Transmit Error Counter (TEC) and Receive Error Counter (REC) Bus Counter and Clock Counter None Hint 67). Which error counter increases when a node repeatedly fails during message transmission? Receive Error Counter Transmit Error Counter CRC Counter Arbitration Counter None Hint 68). Which error counter increases when reception errors are detected? Transmit Error Counter Receive Error Counter Arbitration Counter Identifier Counter None Hint 69). What is the initial error state of a properly functioning CAN node? Error Passive Bus-Off Error Active Recovery Mode None Hint 70). What happens when a node enters the Error Passive state? It immediately disconnects from the bus. It continues communicating but has restricted error signaling. It permanently stops transmitting It changes its identifier. None Hint 71). What happens when the Transmit Error Counter exceeds the Bus-Off threshold? Communication speed doubles. The node enters the Bus-Off state and disconnects from bus communication. Arbitration is disabled. CRC checking is bypassed. None Hint 72). Why is the Bus-Off mechanism important? It increases data throughput. It protects the CAN network from malfunctioning nodes. It reduces cable length. It improves identifier resolution. None Hint 73). Which version of Classical CAN supports only the 11-bit identifier? CAN FD CAN 2.0B CAN 2.0A CAN XL None Hint 74). Which version supports both 11-bit and 29-bit identifiers? CAN 1.0 CAN 2.0A CAN 2.0B LIN None Hint 75). What is the maximum payload size of a Classical CAN Data Frame? 8 bytes 16 bytes 32 bytes 64 bytes None Hint CAN Protocol MCQs for Practice 76). What is the maximum payload size supported by CAN FD? 8 bytes 16 bytes 32 bytes 64 bytes None Hint 77). What does the abbreviation "FD" stand for in CAN FD? Fast Detection Flexible Data-rate Frame Distribution Fault Detection None Hint 78). Which CAN FD feature allows the data portion of a frame to be transmitted faster than the arbitration portion? Error Passive Data Length Code Bit Rate Switching (BRS) Remote Transmission Request None Hint 79). Why is arbitration performed at a lower bit rate in CAN FD? To reduce ECU power consumption. To maintain reliable arbitration across all nodes on the network. To increase the number of identifiers. To eliminate the need for CRC. None Hint 80). An automotive technician measures approximately 120 Ω between CAN_H and CAN_L (with vehicle power OFF). What is the most likely cause? Both termination resistors are correctly installed. One termination resistor is missing or disconnected. The CAN bus is shorted to ground. The CAN controller has failed. None Hint 81). Which higher-layer protocol is widely used in industrial automation based on the CAN Bus? Modbus TCP CANopen MQTT FTP None Hint 82). Which CAN-based protocol is commonly used in heavy-duty commercial vehicles such as trucks and buses? LIN FlexRay SAE J1939 USB None Hint 83). Which higher-layer CAN protocol is primarily designed for factory automation and industrial devices? DeviceNet Ethernet/IP Bluetooth Zigbee None Hint 84). What is the primary purpose of the OBD-II connector in modern vehicles? Charging the battery Vehicle diagnostics and emission monitoring GPS navigation Audio communication None Hint 85). Which communication protocol is commonly used over CAN for ECU diagnostics in modern vehicles? SMTP UDS (Unified Diagnostic Services) HTTP SNMP None Hint 86). What does DTC stand for in automotive diagnostics? Digital Timing Control Diagnostic Trouble Code Differential Transmission Channel Dynamic Torque Calculation None Hint 87). Which tool is most commonly used to observe CAN_H and CAN_L waveforms? Multimeter Oscilloscope Logic Probe Clamp Meter None Hint 88). A correctly functioning High-Speed CAN bus should show which voltage behavior on an oscilloscope during a dominant bit? Both lines remain at 0 V CAN_H rises while CAN_L falls CAN_H falls while CAN_L rises Both lines rise equally None Hint 89). What is a common symptom of missing termination resistors on a CAN network? Increased battery voltage Signal reflections and communication errors C Faster communication Reduced ECU temperature None Hint 90). Which factor most directly limits the maximum cable length of a CAN network? ECU memory size Bit rate Number of processors Supply voltage None Hint 91). Why do automotive manufacturers prefer CAN over point-to-point wiring? CAN requires more wiring CAN reduces wiring complexity, cost, and vehicle weight. CAN eliminates the need for ECUs. CAN operates only wirelessly. None Hint 92). Which CAN message receives bus access first when multiple ECUs transmit simultaneously? The longest message The message with the highest numerical identifier The message with the lowest numerical identifier The message transmitted by the engine ECU None Hint 93). Which of the following is an advantage of CAN FD over Classical CAN? Lower data rate Smaller payload Higher payload capacity and faster data transmission Elimination of arbitration None Hint 94). What is the main purpose of Bit Rate Switching (BRS) in CAN FD? Reduce network security Increase data transmission speed after arbitration Disable CRC checking Reduce payload size None Hint 95). Which CAN technology is designed to support future automotive zonal architectures with significantly higher bandwidth than CAN FD? LIN CAN XL UART I²C None Hint 96). During troubleshooting, an engineer measures approximately 60 Ω between CAN_H and CAN_L with power OFF. What does this usually indicate? The CAN bus is shorted. Both 120 Ω termination resistors are present. No termination resistor exists. The CAN controller is defective. None Hint 97). A CAN node continuously generates transmission errors due to an internal hardware fault. Which CAN feature prevents it from disrupting the entire network indefinitely? Bit Stuffing Fault Confinement with Bus-Off CRC Remote Frame None Hint 98). Which of the following best describes the CAN communication model? Address-oriented communication Message-oriented communication Connection-oriented communication Circuit-switched communication None Hint 99). Which design practice improves the reliability of a High-Speed CAN network? Use long branch (stub) cables. Place termination resistors in the middle of the bus. Use a linear bus with short stubs and proper termination. Connect every ECU in a star topology. None Hint 100). Which statement best summarizes why CAN Bus has become one of the most widely used communication protocols in embedded and automotive systems? It requires a central controller for every communication. It supports only one transmitting node. It combines reliable differential signaling, priority-based arbitration, automatic error detection, fault confinement, and efficient multi-master communication. It replaces all other communication protocols in every application. None Hint Conclusion The Controller Area Network (CAN) Bus Protocol has become one of the most reliable and widely adopted communication standards for embedded systems due to its robust error detection, non-destructive arbitration, fault confinement, and efficient multi-master architecture. Today, CAN is extensively used in automotive electronics, industrial automation, robotics, medical equipment, agricultural machinery, aerospace systems, and many other real-time embedded applications where dependable communication is essential.These 100 MCQs have covered the complete spectrum of CAN Bus concepts, from its fundamentals and physical layer to frame formats, arbitration, error handling, CAN FD, higher-layer protocols, diagnostics, and practical troubleshooting scenarios. Whether you are preparing for engineering examinations, competitive exams such as GATE, technical interviews, or simply strengthening your understanding of embedded communication systems, these questions provide an excellent way to assess and reinforce your knowledge.If you would like a deeper understanding of the concepts behind these questions, including the CAN architecture, working principles, frame structure, arbitration process, error detection mechanisms, CAN FD, and real-world applications, be sure to read our comprehensive CAN Bus Protocol article available on WatElectronics. Studying the detailed article alongside these MCQs will help you build both a strong conceptual foundation and the practical knowledge required for modern embedded systems and automotive engineering. Please fill in the comment box below. Time's up
