P0057 indicates that the heater control circuit for the downstream oxygen sensor on bank 2 is reporting a voltage lower than expected. The heater is used to bring the sensor to operating temperature quickly; a low‑voltage signal suggests an open or high‑resistance path in the heater circuit.
The internal heater coil can open, causing the PCM to see a low voltage on the heater control line.
Damaged, corroded, or disconnected wires between the PCM and the sensor prevent proper current flow.
Corrosion, bent pins, or loose fit can create excessive resistance in the heater feed.
A blown fuse or a relay that does not close will remove power from the heater circuit.
The PCM’s low‑side driver for the heater may fail, but this is uncommon compared with sensor or wiring faults.
PCM replacement is rarely required; the code is almost always caused by the sensor heater, wiring, connector, fuse, or relay.
The downstream sensor mainly monitors catalyst efficiency; a heater fault usually does not affect drivability, but it can increase emissions and fuel use.
With the ignition on and engine off, use a multimeter to check for battery voltage at the sensor heater feed wire and continuity to ground through the heater element.
Only if the underlying fault is repaired; otherwise the code will return once the PCM re‑runs the heater monitor.