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

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.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank. Sensor 2 is the sensor after the catalytic converter.

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

Most 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

What to check, in order

Start with the simplest. You can tick off each step.

1. Check the wiring and connector of the sensor indicated
2. Compare the reading with other engine data while varying the engine speed.
3. Look for exhaust leaks
4. Check the signal in live data with the engine warm
5. Check the fuse and the heater resistance if the code mentions it
6. Replace the sensor if it has power and does not respond

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P22AF means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 2: Fuel injection
• AF: Specific fault in that system

Frequently asked questions

Can I keep driving with code P22AF?

Yes, you can normally drive in moderation, but get it repaired soon: you will use more fuel and the catalytic converter can be damaged over time.

What causes code P22AF?

The most common causes are: 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.

Related codes

• P22AEO2 Sensor Reference Voltage Circuit/Open (Bank 1 Sensor 2)
• P22B0O2 Sensor Reference Voltage Circuit Low (Bank 1 Sensor 2)
• P22B1O2 Sensor Reference Voltage Circuit High (Bank 1 Sensor 2)
• P22BCO2 Sensor Reference Voltage Performance (Bank 2 Sensor 2)
• P2244O2 Sensor Reference Voltage Performance (Bank 1 Sensor 1)
• P0141O2 Sensor Heater Circuit Bank 1 Sensor 2

Sources

• law.cornell.edu: 13 CCR 1968.2
• bosch-motorsport.com: Data Sheet 69034379 Lambda Sensor LSU 4.9
• newtonnet.co.uk: fordobd2012

Values and procedures vary by manufacturer. If it affects brakes, steering, fuel or high voltage, see a professional. Updated: 2026-11-04. How we build these pages.