P0428 means the powertrain control module has detected a voltage signal from the Bank 1 catalyst temperature sensor that is higher than the calibrated limit. This sensor monitors exhaust temperature near the catalytic converter. A circuit-high reading usually points to an open sensor, a short to voltage in the wiring, or a compromised ground circuit rather than a catalyst efficiency failure.
An internal open circuit in the thermistor raises resistance, which the PCM interprets as an abnormally high signal voltage and sets the code.
The sensor signal circuit may be rubbed through and contacting a voltage source, or the sensor ground return may be open, causing the voltage to rail high.
Heat cycling and moisture near the exhaust can push out pins, corrode terminals, or create partial opens that result in a high-voltage reading.
Prolonged exposure to excessive exhaust temperatures can degrade wire insulation and conductors near the sensor, leading to a short or open in the circuit.
A rare internal failure in the PCM’s signal processing or reference voltage circuit could cause an erroneous high reading, but this is not a typical cause.
Short trips are usually safe, but prolonged driving is not recommended if the vehicle uses this sensor for catalyst protection or regeneration control, because incorrect temperature data can lead to converter damage.
No. This is a circuit code for the temperature sensor, not an efficiency code. The catalytic converter itself is often not the root problem.
That is very unlikely. Most P0428 codes are caused by a defective temperature sensor, wiring shorts, or connector issues. The sensor circuit and wiring should be thoroughly tested before the PCM is considered.
No. The catalyst temperature sensor is a separate thermistor-style device. While it may be mounted near the catalytic converter, it is distinct from the oxygen sensor and should not be confused with it.