P2271 code: O2 Sensor Signal Stuck Rich (Bank 1, Sensor 2)
P2271 means o2 Sensor Signal Stuck Rich (Bank 1, Sensor 2). The code says where to look, not what failed — the fix depends on which cause your car actually has.
What P2271 means
P2271 is the rich-side counterpart of P2270: the post-catalyst sensor on bank 1 reports rich continuously and fails to show the behavior the computer expects behind a healthy converter. Because this sensor does not control fueling, the code seldom changes how the car drives; the question is why the signal is pegged. A failing or contaminated sensor and a signal wire shorted to voltage are the direct-fault explanations. The indirect one deserves a check too: an engine running genuinely rich pushes unburned fuel through the converter, which can hold the downstream signal high — so glance for upstream rich evidence like P0172 or P2196 before condemning the sensor. It overlaps with P0138 (high voltage on the same circuit), and like its lean twin it can distort catalyst monitoring until resolved.
P2271 symptoms
- Check-engine light, usually with no driving change
- Failed emissions test
- Fuel smell or poor mileage only when a real rich condition is behind it
What it costs to fix P2271
Typical range: $100–$450 · about ~0.3–1.5 hrs of labor
| If the cause is… | Part | Labor |
|---|---|---|
| O2 sensor (Bank 1, Sensor 2) | $30–$200 | ~0.3–1 hrs |
| Wiring or connector repair | $5–$60 | ~0.5–1.5 hrs |
| Exhaust leak repair (gasket or flange) | $15–$100 | ~0.5–1.5 hrs |
If the sensor is the fault, this is a routine, moderately priced job. The estimate does not cover the scenario where an upstream rich condition is the true cause — that diagnosis leads to fuel-system repairs priced under the relevant code, such as P0172.
The price swings on which cause it turns out to be — so confirm the cause before paying. Diagnose P2271 for my exact vehicle →
How to fix P2271
Easy — basic tools, most owners can do this
- Confirm the upstream side is behaving
Before going under the car, watch Bank 1 Sensor 1 and fuel trims on a warm engine. A normally switching upstream sensor, or a steady correct reading on wideband systems, with trims near zero means the engine isn't feeding the converter excess fuel; negative trims or P2196 and P0172 in memory move the job upstream first.
- See if the rear sensor drops during fuel cut
Record live data on a drive and lift fully off the throttle from speed while still in gear. Fuel shuts off, the exhaust fills with oxygen, and even a tired downstream sensor should fall toward the bottom of its range within a few seconds; one that stays parked high through the whole coast-down is stuck.
- Trace the harness for a short to voltage
Follow the downstream lead for insulation melted on the pipe or worn through against another wire. The giveaway that it's electrical rather than chemical: a warm reading above roughly 1 V, more than a zirconia sensor can produce, or voltage that stays on the harness-side signal pin with the sensor unplugged.
- Inspect the removed sensor for coolant or oil fouling
White or greenish crusting on the tip suggests coolant reaching the exhaust, and heavy black oily deposits suggest oil burning. Either can foul a sensor into reading rich, and the new one will follow unless the source is found with a cooling-system pressure test or compression and leak-down testing.
- Install the new Sensor 2 and rerun the monitors
Fit the replacement with the car on stands, clear codes, and drive a mix of city and highway until the catalyst monitor completes. If a converter-efficiency code shows up afterward, it's now worth taking seriously, because the rear sensor feeding that test can finally be trusted.
DIY or shop? With a scan tool that records live data and a way to get the car safely in the air, this is a manageable home job: the upstream check, the coast-down test, and the harness inspection need no special equipment, and the rear sensor is usually accessible. Bring in a shop when the old sensor shows coolant or oil fouling, since that means an engine fault that needs pressure or compression testing, or when the downstream signal is high because the engine itself runs rich and the cause isn't obvious from trims and codes.
Tools for the DIY steps: Scan tool that records live data · Digital multimeter · Jack stands or ramps · O2 sensor socket · Penetrating oil
Not sure which step applies to your car? Get the likely cause for your exact vehicle before buying anything for P2271.
Start a case with P2271 and your car. Redline weighs these causes against what your car shows, and names the check that would settle it before you buy parts.
Can I drive with P2271?
Redline can’t determine from a symptom or code alone whether your car is safe to drive.
P2271: common questions
Should I check anything before replacing the sensor for P2271?
Do — look for signs the engine is actually running rich: codes like P0172 or P2196, strongly negative fuel trims, a fuel smell, or fouled plugs. A downstream sensor honestly reporting fuel slipping through the converter is not broken, and replacing it would fix nothing.
What is the relationship between P2271 and P0138?
Both concern the bank 1 downstream sensor reading high. P0138 is triggered by circuit voltage above range; P2271 by the signal behaving stuck-rich during the monitoring routine. In practice the suspect list is the same — sensor, wiring short to voltage, or genuine rich exhaust.
Can P2271 cause a false catalytic converter failure?
It can interfere. The converter is graded by comparing upstream and downstream sensor behavior, and a downstream signal stuck rich corrupts that comparison — potentially triggering or masking a P0420. Fix this code first so the catalyst monitor judges the converter on real data.
My car drives perfectly — why fix this at all?
Three reasons: the check-engine light will mask any new problem that appears, an OBD emissions inspection is an automatic fail with the code active, and the computer currently cannot watch your catalytic converter — an expensive part you want monitored.
Related trouble codes
Don’t have a scanner yet? A ~$25 Bluetooth adapter reads codes like P2271 from your phone. See our guide to the best OBD2 Bluetooth adapters. Run a repair shop? See Redline for shops.
Generic OBD-II reference. Manufacturer-specific behavior varies. Confirm with a scan tool and, for safety-related codes, a professional inspection. Cost ranges are reference ranges, not quotes.
Seeing P2271 on your car?
Every problem becomes a Case. Tell Redline what the car is doing: it shows what the evidence supports, what’s still missing, and what to check next, before you approve a repair.
“Inner pad ~1 mm. Outer pad 3 mm.”
Next: check the slide pins move freely before buying parts.