P0548 indicates the Powertrain Control Module (PCM) detects an abnormally low voltage signal from the Exhaust Gas Temperature (EGT) sensor on Bank 2, Sensor 1 (the pre-catalyst sensor on the cylinder bank opposite cylinder #1). This code is set when the sensor circuit voltage falls below the expected range, suggesting an open circuit, short to ground, or a failed sensor.
The sensor itself has failed internally, creating an open circuit or short that produces consistently low voltage reading.
The signal wire between the sensor and PCM has abraded and shorted to chassis ground, pulling voltage low.
Water intrusion or corrosion at the sensor connector or PCM connector can cause poor connectivity and low voltage.
Exhaust heat and vibration can cause the signal wire or ground wire to break or become intermittent.
Rare: The PCM may have a software bug causing incorrect voltage interpretation; reprogramming may resolve.
Very rare: The input circuit within the PCM has failed; this should be diagnosis of elimination only.
Yes, the vehicle will typically operate normally, though you may have slight emissions implications and the Check Engine Light will remain on. However, the underlying issue should be diagnosed to prevent potential catalytic converter damage from undetected overheating.
Because the code indicates a circuit low condition, some technicians may assume the PCM input is faulty before thoroughly checking the much more common sensor and wiring issues. The EGT sensor and its wiring are the root cause in the vast majority of cases.
Costs vary widely by vehicle. Sensor replacement typically ranges from $100-$300 for parts and labor. Wiring repairs if the harness is accessible may cost similar or less. PCM replacement is rare and would be significantly more expensive, often $500-$1000+.