Powertrain, generic (extended)

P22AF O2 Sensor Reference Voltage Performance (Bank 1 Sensor 2)

Check engine lightOn
EmissionsRelevant
Drive cycleRequired
Limp modeNo

P22AF is a plausibility fault on the Nernst-cell (reference voltage) side of the bank 1 downstream wide-band probe: the wiring is intact, but the cell signal does not behave as the controller expects, for instance it cannot be held at its set point or drifts. Typical reasons are an aged cell whose resistance has risen above the roughly 300 ohms Bosch quotes for the LSU 4.9, soot or oil deposits, or a heater that keeps the element too cool. No maker documents this code publicly. CARB requires the OBD system to catch deterioration of voltage, impedance, current or offset of air-fuel sensors behind the aftertreatment before emissions rise too far. Siblings: P22AE open, P22B0/P22B1 low/high, P22BC bank 2, P2244 upstream.

Likely causes

Aged downstream wide-band sensor with raised cell resistance
Soot, oil or coolant deposits on the sensing element
Weak heater or heater control that leaves the element too cold
High-resistance contact in the Nernst-cell circuit

Symptoms

  • Check engine light
  • Downstream oxygen reading sluggish or offset compared with the upstream sensor
  • Catalyst or aftertreatment monitor may report errors as a follow-up

Repair estimate

DifficultyMediumDIY possible
Parts and labour€80–450
Time0.5–2 h

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

Parts involved

oxygen sensor bank1 sensor2oxygen sensor wiringecm

Related codes

P22AEP22B0P22B1P22BCP2244P0141

References: law.cornell.edu, bosch-motorsport.com, newtonnet.co.uk.