P2259 indicates the powertrain control module (PCM) has detected a low voltage condition in the secondary air injection system's 'B' control circuit. The secondary air system pumps fresh air into the exhaust stream during cold start to help warm the catalyst and reduce hydrocarbon emissions. A low-voltage reading typically points to a short to ground, excessive resistance, or a failed component in that control branch.
The solenoid or valve that controls airflow on the B side is the most common failure point; internal coil shorts or carbon contamination can pull the control circuit voltage low.
Corroded, chafed, or broken wires and damaged connectors are a frequent cause of a 'circuit low' reading, especially in the under-hood heat-soak area.
A relay with high resistance contacts can reduce voltage supplied to the control circuit and trigger the code.
A seized or shorted pump motor, or a stuck/leaking combination valve, can drag the circuit voltage down and set the code on some applications.
Although less common, a partially failed fuse, weak ground, or corroded chassis ground can produce a low-voltage signal the PCM interprets as a fault.
Rare. The control module should only be considered after the wiring, solenoid, relay, and pump have all been ruled out with electrical tests.
Yes, in most cases the vehicle will run normally once warm and the code does not typically cause drivability problems. The main practical impact is a likely emissions-test failure, so it should be repaired before a smog or inspection appointment.
Indirectly. The secondary air system helps the catalyst reach operating temperature quickly, and a persistent fault can allow slightly higher exhaust emissions. However, P2259 itself does not mean the catalyst is bad and replacing the converter will not fix it.
Possibly, but that advice is usually wrong for P2259. The secondary air control solenoid/valve, its wiring, and the relay fail far more often than the PCM. A capable technician will confirm the fault electrically before any control module is considered.
On V-configured engines, Bank 1 is typically the side containing cylinder 1 and Bank 2 is the opposite side. The 'A' and 'B' circuit labels can also refer to manufacturer-specific sub-circuits within the air injection system, so consult the vehicle-specific service information for the exact component location.