P2398 is a diesel-specific code indicating the secondary (B) intake air flow position sensor circuit is reading below the expected voltage range. This sensor measures air flow into the engine for proper fuel delivery calculation. A 'circuit low' fault means the signal voltage is too low, suggesting an electrical problem rather than a mechanical air restriction.
The sensor itself is most commonly the direct cause of low voltage output, often due to internal contamination, wear, or thermal damage.
Chafed, pinched, or broken wires in the sensor circuit, particularly near hot engine components or moving parts, can cause low or open circuit conditions.
Oxidation, bent pins, or poor terminal contact at the sensor connector can create high resistance and low signal voltage.
An electrical short pulling the signal circuit to ground will cause the PCM to see consistently low voltage.
Unmetered air entering before the sensor can cause abnormal readings, though this more commonly sets range/performance codes.
A failed engine control module can cause erroneous low voltage readings, but this is the least likely cause and should be diagnosed only after all other possibilities are ruled out.
Driving is not recommended as the engine may enter limp mode to protect itself. If the vehicle seems to run normally, short distances to a repair facility are acceptable, but prolonged driving may cause catalytic converter damage from excess fuel.
Not exactly. P2398 specifically refers to the 'B' position sensor in diesel engines that use multiple air flow sensors. Some diesel engines have a primary MAF and a secondary sensor for redundancy or specific cylinder bank monitoring.
Almost never. While a failed ECM/PCM could theoretically cause this code, it is the least likely cause. Technicians frequently replace sensors, wiring, and connectors before concluding the computer is at fault. Always diagnose the simpler causes first.
Repair costs vary widely by vehicle make and model. Sensor replacement typically costs more for diesel applications than gasoline MAF sensors due to specialized parts. Wiring repairs can range from inexpensive (connector cleaning) to moderate (terminal replacement). Labor rates and parts prices differ significantly by region and shop.