How do you fix 2003 Toyota sequoia error code p0051?

Answer 1

replace O2 sensor ($75-150 depending if OEM) before catalytic converter. need O2 socket ($10) to get at and tough to get to if vehicle isn't at least on a ramp. took me 30 minutes. have to have lights reset.

Answer 2

HO2S (A/F) Sensor Heater Control Circuit Low (Bank 2 Sensor 1)

symptoms
Other than the MIL light illuminating you may not notice any performance issues.

cause
A short in the O2 sensor heater circuit or the sensor itself
A faulty O2 sensor heater
Wiring or connectors are broken or frayed to the sensor or relay
Bad PCM or ECM

The fix
Correct wiring short or loose connector found in inspection.
and/or
Replace the bank 2 sensor 1, O2 sensor
Replace PCM if circuit has failed and no wiring issues present, good O2 sensor