200+ OBD-II Diagnostic Terms and Meanings | Complete Automotive Fault Glossary
Learn 200+ common OBD-II diagnostic terms used in scan tools and DTC descriptions. Understand fault meanings such as Open Circuit, Short to Ground, High Voltage, Intermittent, Circuit High, Circuit Low, Performance, Range, and many more in one complete automotive glossa
Open Circuit
The electrical circuit is interrupted, preventing current from flowing to the component.
Short to Ground
The circuit is unintentionally connected to ground, causing signal loss or excessive current flow.
Short to Voltage
The circuit is accidentally connected to battery voltage, producing an abnormally high electrical signal.
Short Between Wires
Two electrical wires are unintentionally connected, affecting normal circuit operation.
Circuit High
The control module detects a circuit voltage higher than the specified operating range.
Circuit Low
The detected circuit voltage is below the manufacturer's expected operating range.
High Voltage
The measured voltage exceeds the normal operating limit of the monitored circuit.
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Low Voltage
The measured voltage is lower than the minimum required for normal operation.
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High Input
The input signal received by the control module is higher than the expected value.
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Low Input
The input signal is lower than the acceptable operating range.
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Intermittent
The fault appears and disappears intermittently, making it difficult to reproduce.
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Performance
The component is functioning but its performance is outside the expected specification.
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Range / Performance
The measured value is outside the expected range or the component is performing abnormally.
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Signal Stuck High
The signal remains constantly high instead of changing during normal operation.
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Signal Stuck Low
The signal remains constantly low and does not respond to operating conditions.
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No Signal
No electrical signal is detected from the monitored sensor or component.
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Invalid Signal
The received signal is outside valid parameters or cannot be interpreted correctly.
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Erratic Signal
The signal changes unpredictably due to an unstable electrical or mechanical condition.
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Signal Out of Range
The signal exceeds the minimum or maximum value expected by the control module.
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Rationality Fault
The control module determines that the sensor reading is not logically consistent with other system data.
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Sensor Circuit
An electrical fault has been detected in the sensor circuit.
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Actuator Circuit
The actuator control circuit is not operating correctly.
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Control Circuit
The control module has detected a problem in the control circuit.
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Feedback Circuit
The feedback signal from the component is missing or incorrect.
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Driver Circuit
A fault has been detected in the output driver circuit.
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Heater Circuit
The electrical heater circuit is malfunctioning.
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Solenoid Circuit
The solenoid control circuit has an electrical fault.
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Relay Circuit
The relay circuit is not functioning as intended.
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Pump Circuit
The pump electrical circuit has an abnormal condition.
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Motor Circuit
A fault has been detected in the motor control circuit.
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Valve Circuit
The valve control circuit is operating outside normal conditions.
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Open Load
The electrical load is disconnected or an open circuit is detected.
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Shorted Load
The connected electrical load is short-circuited.
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High Resistance
The circuit resistance is higher than the expected specification.
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Low Resistance
The circuit resistance is lower than the specified value.
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Ground Fault
An abnormal ground connection has been detected in the circuit.
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Power Supply Fault
The component is not receiving the correct power supply voltage.
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Battery Voltage High
Battery voltage exceeds the acceptable operating range.
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Battery Voltage Low
Battery voltage is below the required operating level.
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Reference Voltage Fault
The sensor reference voltage is missing or outside specification.
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Current High
The measured current exceeds the expected operating range.
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Current Low
The measured current is below the specified operating range.
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Frequency High
The signal frequency is higher than the control module expects.
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Frequency Low
The signal frequency is lower than the normal operating value.
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Duty Cycle High
The PWM duty cycle is above the specified operating limit.
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Duty Cycle Low
The PWM duty cycle is below the expected operating value.
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Response Too Slow
The component responds slower than the expected response time.
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Response Too Fast
The component reacts faster than the programmed specification.
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Signal Frozen
The signal remains unchanged while operating conditions change.
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Signal Noise
Electrical interference is causing an unstable or noisy signal.
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Unstable Signal
The signal fluctuates abnormally and cannot be considered reliable.
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Data Mismatch
Received data does not match the expected values.
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Parameter Incorrect
One or more operating parameters are outside the valid specification.
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Invalid Calibration
The stored calibration data is invalid or corrupted.
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Programming Error
The control module software contains an invalid configuration.
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Coding Error
Incorrect coding prevents the module from operating properly.
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Adaptation Failed
The control module could not complete the adaptation process.
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Learning Required
A relearn procedure must be completed after repair or replacement.
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Learning Failed
The learning procedure did not complete successfully.
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Initialization Required
The module requires initialization before normal operation.
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Self-Test Failed
The module's built-in self-test did not complete successfully.
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Monitor Failed
A diagnostic monitor detected a fault during system evaluation.
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Monitor Incomplete
The diagnostic monitor has not completed its required test cycle.
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Warm-Up Required
The engine must complete a warm-up cycle before diagnostics can run.
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Readiness Incomplete
One or more OBD readiness monitors have not finished testing.
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Threshold Exceeded
The measured value has exceeded the programmed diagnostic threshold.
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Threshold Not Reached
The monitored value failed to reach the required threshold.
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Value Too High
The detected value is above the maximum allowable limit.
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Value Too Low
The detected value is below the minimum allowable limit.
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Torque Too High
The calculated engine or motor torque exceeds specifications.
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Torque Too Low
The available engine or motor torque is below the expected level.
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Air Flow High
Measured intake airflow is greater than the expected value.
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Air Flow Low
Measured intake airflow is lower than the specified range.
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Fuel Pressure High
Fuel pressure exceeds the manufacturer's specified limit.
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Fuel Pressure Low
Fuel pressure is below the required operating specification.
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Oil Pressure High
Engine oil pressure is higher than the normal operating range.
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Oil Pressure Low
Engine oil pressure is below the safe operating limit.
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Coolant Temperature High
Engine coolant temperature exceeds the normal operating range.
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Coolant Temperature Low
Engine coolant temperature is lower than expected.
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Intake Air Temperature High
The intake air temperature is above the specified operating range.
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Intake Air Temperature Low
The intake air temperature is below the expected operating range.
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Exhaust Temperature High
The exhaust gas temperature exceeds the specified operating limit.
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Exhaust Temperature Low
The exhaust gas temperature is lower than the expected value.
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Boost Pressure High
Turbocharger or supercharger boost pressure is above specification.
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Boost Pressure Low
Boost pressure is below the expected operating level.
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Vacuum Leak
An unwanted air leak is detected in the engine vacuum system.
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Air Leak
Air is entering or escaping from the intake system unexpectedly.
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Fuel Leak
Fuel leakage has been detected in the fuel delivery system.
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Exhaust Leak
Exhaust gases are escaping before reaching the intended outlet.
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Internal Leakage
Internal leakage is reducing the efficiency of the component.
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Blocked Passage
A passage or channel is blocked, restricting normal flow.
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Restricted Flow
The flow of air, fuel, oil, or coolant is restricted.
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Excessive Flow
The flow rate exceeds the specified operating limit.
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Valve Sticking
The valve does not move freely because it is sticking.
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Motor Stalled
The electric motor has stopped unexpectedly during operation.
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Pump Failure
The pump cannot deliver the required flow or pressure.
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Relay Stuck
The relay contacts remain stuck open or closed.
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Fuse Blown
The electrical fuse has opened due to excessive current.
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Actuator Jammed
The actuator cannot move because of a mechanical obstruction.
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Sensor Contaminated
Contamination is affecting the sensor's accuracy and performance.
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Sensor Drift
The sensor output gradually shifts away from its calibrated value over time.
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Signal Offset
The sensor signal has a constant offset from the expected reference value.
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Circuit Resistance High
The circuit resistance exceeds the manufacturer's specified limit.
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Circuit Resistance Low
The circuit resistance is lower than the expected operating value.
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Open Load Detected
The connected electrical load is open or disconnected from the circuit.
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Shorted Load
The electrical load is short-circuited, causing abnormal current flow.
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Excessive Current Draw
The component is drawing more electrical current than specified.
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Insufficient Current
The measured current is below the required operating level.
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Power Relay Fault
The power relay is not switching or operating correctly.
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Main Relay Fault
The main relay has failed or is operating outside specification.
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Ignition Voltage High
The ignition circuit voltage is above the normal operating range.
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Ignition Voltage Low
The ignition circuit voltage is below the required operating level.
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Sensor Voltage High
The sensor output voltage exceeds the expected operating range.
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Sensor Voltage Low
The sensor output voltage is lower than the specified value.
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Actuator Stuck
The actuator cannot move to the commanded position due to an internal or mechanical problem.
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Actuator Response Slow
The actuator responds slower than the expected operating time.
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Actuator Response Fast
The actuator moves faster than the programmed specification.
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Commanded Position Error
The actual component position does not match the commanded position.
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Actual Position Error
The measured position is outside the expected operating range.
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Synchronization Lost
Synchronization between related system components has been lost.
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Clock Signal Error
The clock signal is missing, unstable, or outside the specified frequency.
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Timing Error
The system timing does not match the expected operating values.
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Reference Signal Missing
The required reference signal is not detected by the control module.
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Reference Signal Invalid
The reference signal is present but outside valid operating parameters.
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CAN Timeout
A required CAN network message was not received within the expected time.
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LIN Timeout
The LIN communication response exceeded the allowed time limit.
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Network Configuration Error
The communication network configuration is incorrect or incomplete.
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Gateway Communication Error
The gateway module cannot exchange data correctly with other modules.
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Module Not Responding
The control module failed to respond to communication requests.
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Module Offline
The module is disconnected or unavailable on the communication network.
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Module Reset Detected
An unexpected reset of the control module has been detected.
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Watchdog Reset
The watchdog timer forced the control module to restart.
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EEPROM Check Failed
The EEPROM memory integrity check did not pass successfully.
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Flash Memory Error
An error has been detected in the module's flash memory.
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Software Incompatibility
The installed software version is incompatible with the system.
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Hardware Failure
A hardware component has failed or is no longer operating correctly.
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Control Module Overheated
The control module temperature has exceeded the safe operating limit.
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Sensor Overheated
The sensor temperature is above its specified operating range.
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Cooling System Fault
A malfunction has been detected in the engine or component cooling system.
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Low System Pressure
The system pressure is below the minimum required operating specification.
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High System Pressure
The measured system pressure exceeds the manufacturer's specified operating range.
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Flow Restriction
Air, fuel, oil, or coolant flow is restricted within the system.
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Air in System
Air has entered a system designed to operate with fluid only.
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Fuel Contamination
The fuel contains contaminants that may affect engine performance.
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Water Detected
Water has been detected in a system where it should not be present.
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Moisture Detected
Moisture is interfering with normal electrical or system operation.
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Ground Circuit Open
The ground circuit is open or disconnected, preventing proper operation.
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Power Circuit Open
The power supply circuit is interrupted and cannot deliver voltage.
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Sensor Supply Fault
The sensor power supply voltage is missing or outside specification.
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Control Signal Fault
The control signal is missing, unstable, or outside the expected range.
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Sensor Bias Error
The sensor output has a constant offset from its calibrated reference.
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Reference Value Error
The measured value does not match the programmed reference value.
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Unexpected Signal
A signal has been detected when none was expected by the control module.
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Signal Distortion
The signal waveform is distorted and cannot be interpreted correctly.
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Noise Detected
Electrical interference is affecting the accuracy of the signal.
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Signal Delay
The signal reaches the control module later than expected.
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Data Overflow
The received data exceeds the allowable processing limit.
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Data Underflow
The received data is below the minimum expected operating value.
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Checksum Mismatch
The calculated checksum does not match the expected stored value.
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Communication Lost
Communication between control modules has been interrupted.
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No Communication
The control module cannot communicate with the specified module or device.
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Bus Error
A fault has been detected on the communication bus affecting data transmission.
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Bus Contention
Multiple devices are transmitting simultaneously, causing communication conflicts.
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CAN Bus Off
The CAN controller has entered the Bus-Off state due to excessive communication errors.
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Bus Overload
Communication traffic exceeds the network capacity.
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CAN High Short to Ground
The CAN High communication line is shorted directly to ground.
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CAN Low Short to Ground
The CAN Low communication line is shorted directly to ground.
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CAN High Short to Voltage
The CAN High communication line is shorted to battery voltage.
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CAN Low Short to Voltage
The CAN Low communication line is shorted to battery voltage.
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CAN Open Circuit
The CAN communication circuit is open or disconnected.
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LIN Open Circuit
The LIN communication wire is open or disconnected.
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LIN Short to Ground
The LIN communication line is shorted to ground.
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LIN Short to Voltage
The LIN communication line is shorted to battery voltage.
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Network Wake-Up Failure
The communication network failed to wake up from sleep mode.
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Sleep Mode Failure
The module cannot enter or exit sleep mode correctly.
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Invalid Message
A received communication message contains invalid or corrupted data.
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Message Timeout
The expected communication message was not received within the specified time.
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Authentication Failure
The communication authentication process failed.
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Security Access Denied
The control module denied diagnostic or programming access.
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Diagnostic Session Timeout
The active diagnostic communication session expired due to inactivity.
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Calibration Error
The control module detected invalid or corrupted calibration data.
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Configuration Error
The module configuration does not match the required vehicle settings.
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Variant Coding Error
The vehicle variant coding is incorrect or incomplete.
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Memory Error
An internal memory fault has been detected in the control module.
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RAM Error
The module detected an error in Random Access Memory (RAM).
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ROM Error
The Read-Only Memory (ROM) integrity check has failed.
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Processor Fault
The control module processor is not operating correctly.
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Internal Control Module Fault
An internal hardware or software fault has been detected inside the module.
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Checksum Error
The calculated checksum does not match the stored reference value.
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Data Corrupted
Stored or transmitted data has become corrupted.
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EEPROM Failure
The EEPROM memory cannot reliably store or retrieve data.
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Flash Programming Failed
The software programming process did not complete successfully.
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Bootloader Error
The module bootloader encountered an internal fault.
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Power-On Reset
The control module has restarted after power was restored.
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Unexpected Reset
The module restarted unexpectedly during operation.
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Communication Initialization Failed
The communication network could not be initialized correctly.
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System Initialization Failed
The control system failed to complete its startup sequence.
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Controller Locked
The control module has entered a locked or protected state.
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Safety Shutdown
The system has shut down to prevent damage or unsafe operation.
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Failsafe Mode Active
The control module has activated a protective operating mode due to a detected fault.
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Engine Overspeed
The engine speed has exceeded the maximum allowable RPM limit.
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Engine Underspeed
The engine speed is lower than the expected operating range.
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Idle Speed High
The engine idle speed is higher than the specified value.
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Idle Speed Low
The engine idle speed is below the normal operating specification.
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Engine Stall Detected
The engine has stopped unexpectedly during operation.
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Misfire Detected
One or more cylinders are not combusting fuel correctly.
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Random Misfire
Misfires are occurring on multiple cylinders without a consistent pattern.
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Cylinder-Specific Misfire
A misfire has been detected in a specific engine cylinder.
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Knock Detected
Engine knock or detonation has been detected by the knock sensor.
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Pre-Ignition Detected
The air-fuel mixture ignited before the intended spark timing.
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Lean Condition
The air-fuel mixture contains too much air and not enough fuel.
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Rich Condition
The air-fuel mixture contains too much fuel compared to air.
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Fuel Trim High
Fuel correction values have increased beyond the normal operating limit.
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Fuel Trim Low
Fuel correction values have decreased below the expected range.
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Catalyst Efficiency Low
The catalytic converter is no longer operating at the required efficiency.
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Evaporative Leak Detected
A leak has been detected in the EVAP emission control system.
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Oxygen Sensor Slow Response
The oxygen sensor is responding slower than the expected rate.
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Heater Performance
The sensor heater is operating outside its normal performance range.
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System Too Lean
The engine management system has detected an excessively lean mixture.
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System Too Rich
The engine management system has detected an excessively rich mixture.
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