P22A1: NOx Sensor Circuit High (Bank 1 Sensor 2)

P22A1 flags a raw value from the rear NOx sensor on bank 1 that is higher than anything plausibly left behind the SCR catalyst. GM's 6.6L LML uses 1,500 ppm, or 2,500 ppm in table 14OBDG10; the 3.0L LZ0 and the 2017 small diesels also use 2,500 ppm, Type B after two trips. VW's 2014 Touareg TDI uses 1,655 ppm or a lambda signal above 1.54. Volvo and Mack count P22A1 among codes that point to a damaged outlet sensor and replace that sensor alone. For Ram ProMaster vans, a 2025 Stellantis case (S2525000001) reports P22A1 together with P20EE, asks for standard diagnosis including the DEF condition and states that engineering is still looking for the root cause. GM includes the code in LZ0 software bulletin 24-NA-094. P22A0 is the lower limit, P2203 the front sensor.

Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.

Symptoms

• Malfunction indicator lamp on
• Implausibly high downstream NOx value in live data
• SCR efficiency code P20EE stored alongside

Most likely causes

• Outlet NOx sensor reading high due to internal damage
• DEF quality or dosing problem raising real tailpipe NOx
• Engine software anomaly (GM 3.0L LZ0 2024, bulletin 24-NA-094)

What to check, in order

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

1. Read the codes and the NOx data before and after the SCR catalyst
2. Check the sensor's ground and make sure the signal wire is not receiving voltage from another circuit.
3. Check the sensor's connector and wiring
4. Look for exhaust leaks ahead of the sensor
5. Confirm that the AdBlue/DEF is of good quality
6. Replace the sensor only after ruling out power, ground, and leaks

Good to know

• Repair difficulty: medium
• It affects emissions.

What each character of P22A1 means

• P: Powertrain: engine and transmission
• 2: Generic code: same on every make
• 2: Fuel injection
• A1: Specific fault in that system

Frequently asked questions

Can I keep driving with code P22A1?

You can usually keep driving in the short term, but get it repaired soon: on many diesels, the warning eventually limits starting or engine power.

What causes code P22A1?

The most common causes are: outlet NOx sensor reading high due to internal damage; dEF quality or dosing problem raising real tailpipe NOx; engine software anomaly (GM 3.0L LZ0 2024, bulletin 24-NA-094).

Related codes

• P229ENOx Sensor Circuit (Bank 1 Sensor 2)
• P229FNOx Sensor Circuit Range/Performance (Bank 1 Sensor 2)
• P22A0NOx Sensor Circuit Low (Bank 1 Sensor 2)
• P22A2NOx Sensor Circuit Intermittent (Bank 1 Sensor 2)
• P2203NOx Sensor Circuit High (Bank 1 Sensor 1)
• P20EESCR NOx Catalyst Efficiency Below Threshold (Bank 1)

Sources

• gsi.ext.gm.com: 25OBDG04A
• gsi.ext.gm.com: 14OBDG04 Engine Diagnostics
• static.nhtsa.gov: MC 10074008 2280
• static.nhtsa.gov: MC 10201707 0001

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.