Besides the heater supply, a NOx sensor has a sense line through which its module measures the resistance of the heated element and so infers its temperature. P22A6 reports an electrical fault on that feedback line of the rear sensor on bank 1. GM's 3.0L LZ0 sets it for an open circuit at the HTemp pin, 80 failures in 160 samples, Type A after one trip; GM notes that the Continental Gen 3.5 sensor debounces electrical faults internally for 1.5 s. The 2017 small diesels use the same open-circuit check with 20 failures in 40 samples, also Type A. Volvo and Mack list P22A6 among codes that call for a new outlet sensor; GM bulletin 24-NA-094 names it Heater Feedback Circuit and covers it with an LZ0 software update. P22A8/P22A9 are shorts, P22A7 plausibility, P2208 the front sensor.
Medium severity. Can I keep driving?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.
Bank 1 is the side of the engine with cylinder 1. Inline engines only have this bank.
Symptoms
- Malfunction indicator lamp on after one trip
- Outlet NOx sensor not ready, no downstream value
- SCR warning on the display
Most likely causes
- Open heater sense conductor inside the outlet NOx probe or its lead
- Water or corrosion in the probe connector
- 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.
Good to know
- Repair difficulty: medium
- It affects emissions.
What each character of P22A6 means
- P: Powertrain: engine and transmission
- 2: Generic code: same on every make
- 2: Fuel injection
- A6: Specific fault in that system
Frequently asked questions
Can I keep driving with code P22A6?
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 P22A6?
The most common causes are: open heater sense conductor inside the outlet NOx probe or its lead; water or corrosion in the probe connector; software anomaly (GM 3.0L LZ0 2024, bulletin 24-NA-094).
Related codes
- 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)
- P22AANOx Sensor Heater Sense Circuit Intermittent (Bank 1 Sensor 2)
- P22A3NOx Sensor Heater Control Circuit/Open (Bank 1 Sensor 2)
- P2208NOx Sensor Heater Sense Circuit (Bank 1 Sensor 1)
Sources
- gsi.ext.gm.com: 25OBDG04A
- gsi.ext.gm.com: 17OBDG04 Engine Diagnostics
- static.nhtsa.gov: MC 10201707 0001
- static.nhtsa.gov: MC 11018070 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.