P0051 HO2S Heater Control Circuit Low (Bank 2 Sensor 1)

The heated oxygen sensor on bank 2 is the upstream sensor (sensor 1, before the catalytic converter), used for mixture control. Its heating element brings it quickly to operating temperature. Typically the heater receives battery voltage via a fuse, and the engine control module switches the ground side with a pulsed signal while checking that the circuit state matches the command. P0051 means the control module measures too low a voltage or current in the heater control circuit, for example because of a short to ground or, depending on the system, a burnt-out element. Which physical fault sets the general, low or high code is defined by each manufacturer. Without heating, closed-loop mixture control starts late and cold-start emissions rise. Bank 2 codes occur only on engines with two exhaust banks (V or boxer engines).

Likely causes

Symptoms

• Check engine light on
• Usually no noticeable drivability problem
• Closed-loop control starts late after a cold start
• Emissions test or readiness check failed

Repair estimate

Typical range across vehicles; the real cost depends on what the testing finds.

Parts involved

Related codes

References: law.cornell.edu, saabwisonline.com, en.wikipedia.org.