P2AF0: Intake Air O2 Sensor Negative Current Control Circuit Low Bank 2

P2AF0 is stored when the negative current control circuit of the bank 2 intake oxygen sensor falls below its window. Because the return is meant to sit at a bias of roughly 2.5 V, which Saab's 2010 9-5 lists as the test value on terminal 2 of its exhaust probe, any path to chassis ground pulls it down: insulation worn through at a clip, a crushed connector or an internal short in the sensor. Ford assigns a grounded VM lead on bank 2 exhaust probes to P0151. No manufacturer publishes P2AF0, so the description rests on CARB's range checks and the Bosch pinout. When bank 1 shows P2AE7 as well, suspect a shared harness section first. With the bias gone, the oxygen value of bank 2 is unusable and EGR is cut back. P2AEF is open, P2AF1 high, P2AED the low fault on the pump lead.

Bank 2 is the side without cylinder 1, so it only exists on V or boxer engines.

Symptoms

• Check engine light on
• EGR on bank 2 cut back, possibly higher NOx

Most likely causes

• Return lead worn through at a clip or bracket
• Crushed or damaged sensor connector
• Internal short of the sensor to ground

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 P2AF0 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• A: Hybrid or air and fuel
• F0: Specific fault in that system

Frequently asked questions

Can I keep driving with code P2AF0?

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 P2AF0?

The most common causes are: return lead worn through at a clip or bracket; crushed or damaged sensor connector; internal short of the sensor to ground.

Related codes

• P2AEFIntake Air O2 Sensor Negative Current Control Circuit Open Bank 2
• P2AF1Intake Air O2 Sensor Negative Current Control Circuit High Bank 2
• P2AEDIntake Air O2 Sensor Pumping Current Circuit Low Bank 2
• P2AE7Intake Air O2 Sensor Negative Current Control Circuit Low Bank 1
• P2255O2 Sensor Negative Current Control Circuit Low (Bank 2 Sensor 1)

Sources

• saabwisonline.com: dtc p2237 p2239 p2243 p2251 or p2626
• newtonnet.co.uk: fordobd2012
• bosch-motorsport.com: Data Sheet 69034379 Lambda Sensor LSU 4.9
• law.cornell.edu: 13 CCR 1968.2

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.