Engineering Tools
Fault-Code Library
Understand common OBD fault codes, likely systems, first checks, and when to stop driving.
A fault code identifies a detected condition, not a failed part. Confirm manufacturer-specific subcodes and live data.
Crankshaft / camshaft timing correlation
The ECU sees the crankshaft and camshaft signals outside their expected relationship.
Fuel rail pressure too low
Measured fuel pressure fell below the pressure requested by the engine controller.
Mass-air-flow signal range / performance
Airflow reported by the MAF sensor does not agree with the ECU's calculated operating conditions.
System too lean, bank 1
Fuel trim has reached a lean threshold because the ECU is adding more fuel than expected.
Turbocharger overboost condition
Boost pressure exceeded the ECU's permitted target for the operating condition.
Turbocharger underboost condition
The engine did not produce the boost pressure requested by the controller.
Random / multiple-cylinder misfire
Misfires are occurring across more than one cylinder or without one consistent cylinder pattern.
Exhaust-gas recirculation flow insufficient
Measured or inferred EGR flow is lower than the controller expects.
Catalyst efficiency below threshold, bank 1
Upstream and downstream oxygen-sensor behavior suggests insufficient catalyst oxygen-storage performance.
Diesel particulate filter efficiency below threshold
The ECU calculates that particulate-filter performance is below its required threshold.
Intake-manifold runner position range / performance
The intake-runner position signal is outside the range expected by the controller.
SCR NOx catalyst efficiency below threshold
The SCR system is not reducing NOx emissions as effectively as the ECU expects.
NOx sensor circuit range / performance
A NOx sensor signal or its controller behavior is outside the expected operating range.
DPF differential-pressure sensor range / performance
The pressure signal used to calculate DPF restriction is implausible or outside range.
Diesel particulate filter soot accumulation
Calculated soot loading has reached a level that requires diagnosis before normal operation can continue.
Lost communication with engine control module
One or more modules stopped receiving expected messages from the engine controller.