P22B6: O2 Sensor Pumping Current Trim Circuit Low (Bank 1 Sensor 2)

By its name P22B6 is the low fault on the trim line of the bank 1 downstream wide-band probe, i.e. the lead to the calibration resistor in a Bosch-style sensor connector. GM's diesel tables use the slot differently: they set it when the oxygen value reported by the second NOx sensor falls below its physical minimum, less than -4 % in 200 of 250 samples in the 2016 table, with the engine in combustion mode and no NOx sensor fault pending. It is a Type B code with two trips. GM also lists P22B6 in PIP5468 for 2017-2018 Silverado/Sierra HD with the 6.6 L5P, where leaking charge-air ducting can set it, and in 21-NA-149 for the 3.0 LM2. P22B5 is the open, P22B7 the high counterpart, P22C3 bank 2. The lamp comes on.

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
• Negative oxygen percentage shown for the downstream sensor in live data
• Possible additional boost or air-flow codes when charge air leaks

Most likely causes

• Faulty downstream NOx/oxygen sensor delivering an impossible oxygen value
• Leaking charge-air cooler ducting (GM 6.6 L5P)
• Trim or signal wire shorted to ground in the harness

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 P22B6 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 2: Fuel injection
• B6: Specific fault in that system

Frequently asked questions

Can I keep driving with code P22B6?

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 P22B6?

The most common causes are: faulty downstream NOx/oxygen sensor delivering an impossible oxygen value; leaking charge-air cooler ducting (GM 6.6 L5P); trim or signal wire shorted to ground in the harness.

Related codes

• P22B5O2 Sensor Pumping Current Trim Circuit/Open (Bank 1 Sensor 2)
• P22B7O2 Sensor Pumping Current Trim Circuit High (Bank 1 Sensor 2)
• P22C3O2 Sensor Pumping Current Trim Circuit Low (Bank 2 Sensor 2)
• P2627O2 Sensor Pumping Current Trim Circuit Low (Bank 1 Sensor 1)

Sources

• gsi.ext.gm.com: 16OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 18OBDG04 Engine Diagnostics
• gsi.ext.gm.com: 25OBDG04B
• static.nhtsa.gov: MC 10123220 9999

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.