OBD-II Diagnostic Trouble Code
P2271 — O2 Sensor Signal Stuck Rich Bank 1 Sensor 2
P2271 indicates the bank 1 sensor 2 oxygen sensor stayed rich and did not switch lean when the ECM leaned the mixture, such as during deceleration fuel cutoff. It applies to gasoline trucks with downstream O2 sensors.
Severity 2/5
Less common on commercial trucks
Service soon
Severity
Service soon
O2 Sensor Signal Stuck Rich Bank 1 Sensor 2
Code
P2271
Category
Powertrain
Subsystem
Emissions
Truck-relevant
Less common
What this means for truckers
P2271 (O2 Sensor Stuck Rich B1S2) — opposite of P2270.
Before you replace parts — try this first
P2271 on the Emissions system is most often failed or contaminated downstream o2 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
Typically only a check-engine light; occasionally accompanied by poor fuel economy or a catalyst code if the engine is running rich.
Common causes
- CommonFailed or contaminated downstream O2 sensor ($120–$350)
- OccasionalEngine running rich (leaking injector, high fuel pressure) ($150–$900)
- OccasionalSignal wire shorted to voltage or heater circuit ($80–$300)
- RareCoolant or oil contamination of the sensor ($120–$2000)
How to fix
Monitor sensor voltage during decel fuel cut; it should drop low
When to use: To confirm the sensor is stuck
Check fuel trims and fuel pressure for a rich condition
When to use: When trims are strongly negative
Inspect sensor wiring for shorts
When to use: When the voltage is unusually high
Replace the downstream O2 sensor
When to use: When the engine and wiring are fine
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
- → P229E — NOx Sensor Circuit Bank 1 Sensor 2
- → 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 P2271?
P2271 is severity 2 — service this week. Not an immediate stop, but ignoring it usually compounds the problem. Most common cause for this code is a worn sensor or minor performance fault that won't strand you today but will get more expensive the longer you wait.
How much does it cost to fix P2271 on a commercial truck?
Total repair cost ranges $80–$2000 depending on the root cause. The cheapest fix is usually the first one listed below — Failed or contaminated downstream O2 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 P2271 fail a DOT inspection?
Yes — P2271 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 P2271 and related codes?
P2271 is closely related to: P229E (NOx Sensor Circuit Bank 1 Sensor 2), 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 (emissions) 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 P2271 is set without the companions, the issue is more isolated.
How do I prevent P2271 from coming back after a repair?
For P2271 (O2 Sensor Signal Stuck Rich Bank 1 Sensor 2), prevention centers on the emissions system. Keep up with PM on the EGR system — clean the valve at 200K miles. Use OEM-spec air filters. Don't ignore minor codes; they often escalate into bigger emissions failures.