OBD-II Diagnostic Trouble Code
P229E — NOx Sensor Circuit Bank 1 Sensor 2
P229E indicates a circuit fault on the bank 1 sensor 2 NOx sensor, which on heavy diesels is normally the outlet NOx sensor after the SCR catalyst. The fault is usually an internal sensor or communication fault reported by the sensor's control module.
Severity 4/5
Truck-relevant
Stop within 50 mi
Severity
Stop within 50 mi
NOx Sensor Circuit Bank 1 Sensor 2
Code
P229E
Category
Powertrain
Subsystem
Aftertreatment
Truck-relevant
Yes
What this means for truckers
Stop within ~50 miles on a Cummins X15, Detroit DD15, PACCAR MX-13. Driving longer risks damaging adjacent components (turbo housing, head gasket, aftertreatment) and turning a $300 fix into a $3,000 fix.
Before you replace parts — try this first
P229E on the Aftertreatment system is most often failed outlet nox sensor — not a dead part. On commercial diesels especially, work these in order before spending money on parts:
- Confirm the symptoms. Match what your truck is doing to the Symptoms section below. If the code is set but the symptoms are not there, clear the code and re-test after a drive cycle — it may not return.
- Clean and dry the sensor connector. Water, road salt, or oil seeping into a connector is the #1 fake sensor failure. Disconnect, look for green corrosion or moisture, spray with electrical contact cleaner, dry, reseat. Many faults clear here for $0.
- Inspect the wiring harness. Trace the wire from the sensor toward the ECM — look for chafing against the engine block, melted insulation near the turbo or exhaust, or pinch points where a clamp has rubbed through.
- Test the sensor before swapping it. Most Common Causes (below) list the expected voltage or resistance range — a $20 multimeter saves a $300 sensor swap that does not fix the problem.
- Only then, replace the part. Use the OEM or a tier-1 aftermarket. Cheap sensors throw the same code in two weeks.
Symptoms
Emissions or check-engine light and loss of SCR efficiency monitoring. If not repaired, most trucks enter a timed inducement derate and speed limit.
Common causes
- CommonFailed outlet NOx sensor ($450–$1200)
- CommonDamaged harness or connector at the sensor module ($100–$400)
- OccasionalLoss of power, ground or CAN to the sensor ($100–$450)
- RareControl module fault ($800–$2500)
How to fix
Check power, ground and CAN at the outlet NOx sensor module
When to use: First check
Inspect wiring along the exhaust for heat damage
When to use: When supply is intermittent
Replace the outlet NOx sensor
When to use: When wiring is good
Run SCR performance test
When to use: After repair to verify
Affects most
No specific vehicle pattern found in our complaint database. This code can appear on any vehicle that supports OBD-II diagnostics.
Related
- → Browse all DTC trouble codes
- → Decode a VIN to check codes for your truck
- → Owner-operator maintenance guides
- → P2200 — NOx Sensor Circuit Bank 1
- → P229F — NOx Sensor Bank 1 Sensor 2
- → P22A4 — Reductant Heater B Control Circuit/Open
- → P22A5 — Reductant Heater B Control Circuit Low
- → P22A6 — Reductant Heater B Control Circuit High
Frequently Asked Questions
Can I drive with code P229E?
Drive with caution. P229E is severity 4 — stop within ~50 miles. Most commercial diesel codes at this severity (turbo, fuel rail, transmission solenoid) can damage adjacent expensive components if left unrepaired. Get to a service location before highway-speed loads.
How much does it cost to fix P229E on a commercial truck?
Total repair cost ranges $100–$2500 depending on the root cause. The cheapest fix is usually the first one listed below — Failed outlet NOx sensor — which is also the most common. On commercial trucks the cost is usually higher than passenger vehicles due to part availability and shop labor rates ($120–185/hour at most truck shops, vs $90–130 at general auto shops). DIY-capable fixes (sensors, hoses, filters) are at the low end; major component replacements (turbo actuator, high-pressure fuel pump, transmission solenoid pack) are at the high end. Always diagnose with a scan tool BEFORE replacing parts — guessing wrong on a $1,500 turbo actuator when the actual issue was a $30 boost hose is a common expensive mistake.
Will P229E fail a DOT inspection?
Yes — P229E is an emissions-related code, and DOT inspectors check emissions compliance. An active emissions code with a check engine light can result in an out-of-service violation under FMCSA Part 393. The truck typically can't be moved until the code is cleared. Repeated emissions violations escalate to CSA scores.
What's the difference between P229E and related codes?
P229E is closely related to: P2200 (NOx Sensor Circuit Bank 1), P229F (NOx Sensor Bank 1 Sensor 2), P22A4 (Reductant Heater B Control Circuit/Open), P22A5 (Reductant Heater B Control Circuit Low). These codes share the same subsystem (aftertreatment) and often appear together. If you see this code, scan for the full code list — fixing the root cause usually clears multiple companion codes at once. If only P229E is set without the companions, the issue is more isolated.
How do I prevent P229E from coming back after a repair?
For P229E (NOx Sensor Circuit Bank 1 Sensor 2), prevention centers on the aftertreatment system. Run quality DEF (verify supplier — BlueDEF, PEAK, Yara Air1). Don't skip parked regens — when the dash asks for one, do it. Avoid extended idle time which fouls the DPF. Replace NOx sensors at the OEM interval (typically 400K miles).