P22AA: NOx Sensor Heater Sense Circuit Intermittent (Bank 1 Sensor 2)

P22AA covers a heater sense line on the rear NOx sensor of bank 1 that fails only now and then. The module uses this line to read the element temperature and keep the heater on target; if the reading drops out or jumps for short moments, the temperature control briefly loses its reference and the sensor may fall out of its ready state. No manufacturer publicly documents a threshold or a bulletin for P22AA, and GM, Ford and VW do not list it in their published tables. CARB asks for continuous monitoring of NOx sensor heater circuits, and smart sensors report the heater circuit state (open, short, no error) over CAN. In practice, check terminal grip, cable routing near hot parts and water ingress. P22A6, P22A8 and P22A9 are the steady faults, P2212 the front sensor.

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

Symptoms

• Malfunction indicator lamp that may come and go
• Outlet NOx sensor intermittently not ready

Most likely causes

• Loose or corroded terminal in the probe connector
• Lead near the exhaust cracked by heat or vibration
• Intermittent internal contact fault in the probe

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. Gently move the wiring with the engine running and watch whether the reading changes.
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 P22AA means

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

Frequently asked questions

Can I keep driving with code P22AA?

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 P22AA?

The most common causes are: loose or corroded terminal in the probe connector; lead near the exhaust cracked by heat or vibration; intermittent internal contact fault in the probe.

Related codes

• P22A6NOx Sensor Heater Sense Circuit (Bank 1 Sensor 2)
• P22A7NOx Sensor Heater Sense Circuit Range/Performance (Bank 1 Sensor 2)
• P22A8NOx Sensor Heater Sense Circuit Low (Bank 1 Sensor 2)
• P22A9NOx Sensor Heater Sense Circuit High (Bank 1 Sensor 2)
• P2212NOx Sensor Heater Sense Circuit Intermittent (Bank 1 Sensor 1)

Sources

• law.cornell.edu: 13 CCR 1968.2
• ni.com: NOx Sensor USB UM RevA
• hella.com: nitrogen oxide sensor nox sensor

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.