Welcome to our free on-board diagnostics quiz designed to challenge veteran technicians and curious drivers alike! In this engaging obd system quiz, you'll put your understanding of error codes, self-monitoring functions, and continuous monitors are run for systems that could impact emissions to the test. Whether you're prepping for a vehicle diagnostics test or simply want to hone your OBDII quiz skills, this car diagnostic quiz covers it all. If you've tackled our car electrical test or brushed up with a basic car knowledge warm-up, you're ready to dive in. Ready to prove your expertise? Let's get started!
What does "OBD" stand for in automotive diagnostics?
On-board Diagnostics
Off-board Diagnostics
On-board Display
On-board Device
OBD stands for On-board Diagnostics, referring to the vehicle's self-diagnostic and reporting capability. The system monitors various subsystems and components to ensure proper operation. When a fault is detected, the OBD system generates trouble codes for technicians to read. For more details see On-board Diagnostics - Wikipedia.
Which OBD standard became mandatory for all cars and light trucks sold in the United States from 1996 onwards?
OBD I
EOBD
OBD II
OBD III
OBD-II was mandated in the US for all cars and light trucks starting in 1996. It standardized diagnostic connectors, communication protocols, and a universal set of diagnostic trouble codes. This allowed technicians and consumers to use generic scan tools on any compliant vehicle. For a detailed history, refer to EPA OBD-II Mandate.
The Malfunction Indicator Lamp (MIL) on a vehicle dashboard is commonly known as:
Service Oil Soon Light
Check Engine Light
Coolant Temperature Warning Light
Battery Warning Light
The MIL is commonly referred to as the Check Engine Light (CEL) or Service Engine Soon lamp. It illuminates when the vehicle's computer detects an emissions-related fault. The lamp provides an initial indication that a diagnostic scan tool should be connected to retrieve trouble codes. Additional information is available at OBD Solutions.
How many pins are there on the standard OBD-II Data Link Connector (DLC) in most vehicles?
20
16
8
12
The OBD-II interface uses a standardized 16-pin, trapezoidal connector defined by SAE J1962. This connector allows a scan tool or code reader to communicate with the vehicle's powertrain control module. All compliant vehicles must use this connector shape and pin layout. More details are listed at OBD-II PIDs - Wikipedia.
Which of the following is a Controller Area Network (CAN) based OBD-II communication protocol?
SAE J1850 PWM
ISO 15765-4
ISO 9141-2
SAE J1850 VPW
ISO 15765-4 specifies the use of CAN (Controller Area Network) for OBD-II diagnostics. CAN became the dominant protocol for high-speed vehicle networks starting in the late 1990s. It offers robust error checking and multi-master communication. For more, see SAE J1979.
What does the term "DTC" stand for in OBD systems?
Diagnostic Trouble Code
Drive Train Condition
Direct Temperature Circuit
Dynamic Timing Control
DTC stands for Diagnostic Trouble Code, which is a standardized code stored when the vehicle detects a malfunction. These codes help identify the system or component causing an issue. Technicians retrieve DTCs with a scan tool to diagnose faults. For definitions, visit Diagnostic Trouble Code - Wikipedia.
Which sensor measures the mass of air entering the engine for fuel calculation?
Throttle Position sensor
Manifold Absolute Pressure (MAP) sensor
Mass Air Flow (MAF) sensor
Oxygen sensor
The Mass Air Flow (MAF) sensor measures the actual mass of air entering the engine. This information enables the PCM to calculate the correct fuel quantity for optimal combustion. It is a critical input in modern fuel-injection systems. Learn more at Engine Basics.
Which of the following is a generic (SAE defined) Powertrain DTC category code?
B1xxx
U3xxx
P0xxx
P2xxx
Generic powertrain codes are in the P0xxx range and are defined by SAE for all manufacturers. Codes in P2xxx are manufacturer-specific variants, while B and U codes refer to body and network issues. Recognizing P0xxx codes helps technicians apply universal diagnostic steps. See OBD-Codes.com for a full list.
What is a readiness monitor in an OBD-II system?
A tool to reset DTCs
A device measuring engine temperature
A self-test for emissions components required for inspection
A line in the wiring harness
Readiness monitors are built-in tests that check the performance of emissions-related components. They must complete successfully before an inspection or emissions test can pass. The PCM tracks monitor status and indicates incomplete monitors to the scan tool. For more, visit OBD FAQ.
What does freeze frame data refer to in OBD-II diagnostics?
Stored VIN numbers
Real time live data stream
Stored ECM update history
Snapshot of operating conditions when a DTC is set
Freeze frame data is a snapshot of key sensor readings at the moment a fault code is stored. This information helps technicians understand the context of the failure event. Most systems capture up to a dozen parameters in the freeze frame. Detailed information can be found at Volvo FAQ.
Which OBD-II Mode is used to retrieve current powertrain data such as engine RPM and vehicle speed?
Mode 01
Mode 03
Mode 02
Mode 04
Mode 01 in OBD-II is used to request live data PIDs like RPM, temperature, and speed. It provides real-time information for active diagnostics. Scan tools poll Mode 01 parameters continuously during troubleshooting. More details are available at OBD-II PIDs - Wikipedia.
Which OBD-II Mode retrieves pending DTCs that have not yet triggered the MIL?
Mode 07
Mode 03
Mode 09
Mode 06
Mode 07 returns pending trouble codes that have been detected but have not met the criteria to illuminate the MIL. This allows early detection of intermittent faults. Pending codes become confirmed if the fault recurs. Learn more at OBD Tester.
During a key-on engine-off (KOEO) bulb check, what does the MIL do if the system is functioning correctly?
Flashes continuously
Dims gradually
Stays on constantly
Flashes briefly then remains off
At KOEO, the PCM illuminates the MIL briefly to verify the bulb and circuit integrity. If no faults are detected, the lamp will go out and remain off. A continuous flash or steady illumination indicates a circuit issue or fault. Further reading at OBD Solutions.
What is monitored by the OBD-II evaporative emissions (EVAP) system readiness test?
Exhaust gas oxygen concentration
Transmission fluid pressure
Integrity of fuel tank and lines
Coolant temperature range
The EVAP system monitor checks for leaks in the fuel tank, filler cap, and associated lines. A small vacuum is drawn to verify system integrity and detect leaks. An incomplete monitor can fail an emissions inspection. Details are at Wikipedia.
What does a "P0171" code indicate?
System too rich (Bank 1)
System too lean (Bank 1)
Catalyst efficiency below threshold
Misfire detected
P0171 means the fuel trim is pulling maximum correction toward lean detected on Bank 1. This suggests an air leak, faulty sensor, or fuel delivery issue. Technicians often inspect intake gaskets and MAF sensors first. More diagnosis tips at OBD-Codes.com.
Which OBD-II Mode allows access to test results of onboard diagnostics not continuously monitored?
Mode 04
Mode 06
Mode 03
Mode 01
Mode 06 returns quantitative test results for non-continuous monitors like EGR and catalyst efficiency. It provides raw data such as sensor limits and error thresholds. Mode 06 helps diagnose component performance before a MIL is set. For specifics, see Wikipedia.
When diagnosing a misfire, which OBD-II parameter is most directly useful?
Fuel pressure
Battery voltage
Misfire counters per cylinder
Engine coolant temperature
Misfire counters (Mode 06 PIDs) track the number of misfire events per cylinder. This data helps pinpoint which cylinder is misfiring and the severity. The PCM increments counters when combustion anomalies occur. Detailed info at AA1Car.
What voltage range does a typical narrowband oxygen sensor output?
1.5 to 3.5 volts
0.5 to 4.5 volts
0.1 to 0.9 volts
5 to 10 volts
A narrowband O2 sensor produces a voltage between approximately 0.1 and 0.9 V relative to the oxygen level in the exhaust. Around 0.45 V indicates stoichiometric conditions. The PCM uses this feedback to adjust fuel trim. More details at Wikipedia.
In OBD-II, what does the term "K-line" refer to?
High speed CAN bus
Power supply line for sensors
Ground reference voltage line
UART-based serial line for diagnostics
K-line is the single-wire, bidirectional serial communication line used in ISO 9141-2 and ISO 14230 protocols. It allows the scan tool to send and receive diagnostic messages with the ECU. Unlike CAN, it operates at lower speeds. Additional protocol info at Wikipedia.
Which OBD-II test ensures the catalytic converter is functioning properly?
EGR System Monitor
Catalyst Efficiency Monitor
Evaporative Emissions Monitor
Oxygen Sensor Heater Monitor
The Catalyst Efficiency Monitor compares the oxygen sensor responses before and after the catalytic converter. It checks conversion efficiency and sets a DTC if performance falls below a threshold. This monitor runs under specific conditions to ensure accuracy. More on this test at OBD-Codes.com.
Which organization defines the SAE J1979 standard for OBD-II diagnostic services?
ASTM
SAE International
ISO
IEEE
SAE International publishes the J1979 standard that outlines OBD-II diagnostic services and PIDs. It specifies how scan tools should request data from the vehicle's control modules. While ISO defines protocols, J1979 is the reference for OBD-II services in North America. For the full standard, visit SAE J1979.
What is the primary purpose of OBD-II Mode 09?
Read pending codes
Clear DTCs
Test non-continuous monitors
Retrieve vehicle information like VIN
Mode 09 provides access to vehicle information such as Vehicle Identification Number (VIN), calibration IDs, and PCM serial numbers. This mode allows technicians to confirm correct vehicle data. It does not clear codes or retrieve pending DTCs. See OBD Tester for details.
On a CAN bus network, what is the bus termination resistance value at each end?
60 ohms
30 ohms
120 ohms
240 ohms
A CAN bus requires termination resistors of 120 ? at each end of the differential pair to prevent signal reflections. Two 120 ? resistors in parallel yield an effective 60 ? across the bus. Proper termination ensures reliable communication at high data rates. For more information, see CAN bus - Wikipedia.
How does the OBD-II system detect an open circuit in the oxygen sensor heater circuit?
By comparing heater current to expected value
Checking manifold vacuum
Monitoring fuel trims
Measuring throttle position
The PCM monitors the heater circuit's resistance and current draw to verify its integrity. If the measured current is below a specified threshold, it flags an open circuit. This prevents the oxygen sensor from reaching operating temperature. Further technical details at AutoNerdz.
Which ISO standard covers the keyword protocol 2000 (KWP2000) used in OBD communications?
ISO 9141
ISO 15765
ISO 11898
ISO 14230
ISO 14230 specifies the KWP2000 diagnostic protocol used in OBD-II communications. It defines message formats, timing, and data link layer services. KWP2000 can run over K-line or CAN physical layers. For the official standard, see ISO 14230.
What does Mode 03 in OBD-II diagnostics retrieve?
Vehicle identification
Live sensor data
Stored emissions-related DTCs
Pending codes
Mode 03 returns confirmed Diagnostic Trouble Codes that have triggered the MIL. These codes are stored after the PCM detects a fault that meets certain criteria. Mode 03 data helps technicians review historical faults. For more, refer to OBD-Codes.com.
Which of these parameters is NOT typically accessed through OBD-II PIDs?
Transmission fluid viscosity
Engine RPM
Vehicle speed
Coolant temperature
OBD-II PIDs cover engine, transmission, and emissions parameters but do not include fluid viscosity measurements. Transmission fluid viscosity is not a monitored variable in standard OBD-II. Technicians use other tools to assess fluid condition. More information at Wikipedia.
What is the minimum number of freeze frame data sets the OBD-II system must record per DTC?
2
8
4
1
The OBD-II specification requires at least one freeze frame per diagnostic trouble code. This single snapshot captures conditions at the moment the code is stored. While some manufacturers keep multiple frames, one is the minimum. For details, see OBD2 FAQ.
Which diagnostic trouble code category indicates issues in the vehicle's chassis systems?
P codes
C codes
B codes
U codes
Diagnostic Trouble Codes starting with 'C' are reserved for chassis-related faults such as suspension or steering components. 'B' codes refer to body systems, 'P' codes to powertrain, and 'U' codes to network communication. Understanding code categories aids systematic diagnostics. More at OBD-Codes.com.
In OBD-III proposals, how is real-time emissions monitoring achieved?
Via wireless data transmission to authorities
Optical scanning at roadblocks
Paper log submission
Manual inspection at service stations
OBD-III concepts involve on-board systems transmitting emissions data wirelessly to regulatory agencies or centralized databases. This approach aims to enable continuous monitoring beyond periodic inspections. It would alert officials to high-emitting vehicles in real time. For regulatory details, see EPA OBD-III.
Under the Unified Diagnostic Services (UDS) protocol ISO 14229, what service ID is used for 'Read Data by Identifier'?
0x10
0x19
0x2E
0x22
In the UDS protocol (ISO 14229), service 0x22 is defined for reading data by identifier (DID). It allows access to various ECU parameters and data fields using standard or manufacturer-specific IDs. Other service IDs perform different functions such as security and programming. Full service list at UDS - Wikipedia.
0
{"name":"What does \"OBD\" stand for in automotive diagnostics?", "url":"https://www.quiz-maker.com/QPREVIEW","txt":"What does \"OBD\" stand for in automotive diagnostics?, Which OBD standard became mandatory for all cars and light trucks sold in the United States from 1996 onwards?, The Malfunction Indicator Lamp (MIL) on a vehicle dashboard is commonly known as:","img":"https://www.quiz-maker.com/3012/images/ogquiz.png"}
Score5/31
Easy1/10
Medium3/10
Hard1/9
Expert0/2
AI Study Notes
Email these to me
You can bookmark this page to review your notes in future, or fill out the email box below to email them to yourself.
Study Outcomes
Understand OBD-II fundamentals -
Identify the key components and communication protocols of the on-board diagnostics system to grasp how vehicle sensors provide real-time data.
Analyze diagnostic trouble codes -
Decode common vehicle error codes and interpret their numeric and alphanumeric sequences for efficient troubleshooting.
Apply self-monitoring functions -
Explain how continuous monitors are run for systems that could trigger emissions alerts and leverage this information to maintain compliance.
Evaluate system readiness monitors -
Assess the status of vehicle readiness tests to determine whether specific systems have completed self-diagnostics before an emissions check.
Interpret OBD system quiz results -
Use feedback from the vehicle diagnostics test to gauge your proficiency in vehicle diagnostics and pinpoint areas for further study.
Apply troubleshooting strategies -
Utilize knowledge gained from the car diagnostic quiz to outline step-by-step diagnostic procedures for DIY car repairs.
Cheat Sheet
OBD-II Communication Protocols -
Understanding the five primary protocols (CAN, ISO9141, KWP2000, J1850 VPW, J1850 PWM) is essential for acing any on-board diagnostics quiz. Remember the mnemonic "I Can Kick Jolly" (ISO, CAN, KWP, J1850 VPW, J1850 PWM) to recall each protocol quickly. Accurate knowledge of the diagnostic link connector pinouts ensures seamless communication with scan tools (SAE J1962).
Diagnostic Trouble Code (DTC) Structure -
Every DTC follows the format P0xxx, where "P" stands for Powertrain, "0" indicates a generic code, and "xxx" identifies the specific fault (e.g., P0171 for a lean condition). In an obdii quiz, you may be asked to decipher codes using the formula: letter + system digit + fault digits. Practice with sample codes from the SAE J2012 standard to build confidence.
Readiness Monitors & Freeze Frame Data -
Continuous monitors are run for systems that could trigger emissions alerts, but readiness monitors only complete after a series of drive cycles without resets. Freeze frame captures sensor data at the moment a fault occurs - use this "snapshot" to pinpoint causes. For your vehicle diagnostics test, remember: Monitor status = CMP (Complete), INC (Incomplete), and N/A (Not Applicable).
Oxygen Sensor Efficiency & Air - Fuel Ratio -
O2 sensors measure residual oxygen in the exhaust to maintain the stoichiometric 14.7:1 air - fuel ratio. A popular memory trick is "14.7 Eats Perfectly" to recall the ideal ratio for gasoline engines. In a car diagnostic quiz, you may calculate sensor voltage changes (0.1 - 0.9 V) to assess rich or lean conditions.
On-Board Self-Monitoring for Emissions Systems -
The EVAP, catalyst, oxygen sensors, and EGR systems each have continuous or non-continuous self-tests regulated by the EPA OBD-II standard. For a vehicle diagnostics test scenario, know that the EVAP purge monitor starts after three cold starts and a fuel level between 15 - 85%. Studying official EPA documentation ensures your answers reflect current regulatory requirements.
