P22B9: O2 Sensor Positive Current Control Circuit Low (Bank 2 Sensor 2)

P22B9 means the positive current control (pump-current) line of the bank 2 downstream wide-band probe reads below its allowed band, most often because the lead has worn through and touches ground. No maker documents this code publicly, so the logic can only be inferred from the bank 1 and upstream relatives: GM lists P22AC for the 3.0 Duramax LM2 without a threshold, Saab treats the upstream P2238 as a Type B fault, and Ford books upstream shorts as P0131. CARB requires out-of-range detection on air-fuel sensors behind the aftertreatment. The fault needs a V or boxer engine with a wide-band probe after each catalyst. P22B8 is the open, P22BA the high variant, P22AC the bank 1 code. A lit warning lamp is usually the only symptom.

Bank 2 is the side without cylinder 1, so it only exists on V or boxer engines. Sensor 2 is the sensor after the catalytic converter.

Symptoms

• Check engine light
• Bank 2 downstream oxygen value at an extreme

Most likely causes

• Pump-current wire chafed through and shorted to ground
• Internal short in the bank 2 downstream sensor
• Water in the connector

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. With the connector unplugged, check whether the signal wire is making contact with ground.
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 P22B9 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 2: Fuel injection
• B9: Specific fault in that system

Frequently asked questions

Can I keep driving with code P22B9?

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 P22B9?

The most common causes are: pump-current wire chafed through and shorted to ground; internal short in the bank 2 downstream sensor; water in the connector.

Related codes

• P22B8O2 Sensor Positive Current Control Circuit/Open (Bank 2 Sensor 2)
• P22BAO2 Sensor Positive Current Control Circuit High (Bank 2 Sensor 2)
• P22ACO2 Sensor Positive Current Control Circuit Low (Bank 1 Sensor 2)
• P2241O2 Sensor Positive Current Control Circuit Low (Bank 2 Sensor 1)

Sources

• law.cornell.edu: 13 CCR 1968.2
• saabwisonline.com: dtc p2237 p2239 p2243 p2251 or p2626
• 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.