P1151
Lack of Upstream Heated Oxygen Sensor Switch — Sensor Indicates Lean (Bank 2)
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The P1151 is the Bank 2 counterpart of the P1131 code and is specific to Ford vehicles. It indicates that the upstream heated oxygen sensor on Bank 2 (the side of the engine that does not contain cylinder #1) is not switching properly and is consistently reporting a lean condition. This may reflect a true lean mixture or a sensor malfunction.
In V6 and V8 Ford engines, this code often appears alongside P1131, which would suggest a common cause like a fuel pump issue. When P1151 appears alone, it typically points to a problem isolated to Bank 2 — most commonly a vacuum leak on that side of the intake, a bad O2 sensor, or clogged injectors feeding Bank 2 cylinders.
This code should be addressed within a week. Prolonged driving with a lean condition can overheat the catalytic converter, cause misfires, and lead to more expensive repairs. A mechanic will typically perform a smoke test for vacuum leaks, check fuel trim data with a scan tool, and monitor the O2 sensor waveform to determine whether the sensor or the engine's air-fuel mixture is at fault.
Severity
Symptoms
- •Check engine light is on
- •Engine hesitation or stumbling under load
- •Decreased fuel economy
- •Rough idle or stalling at idle
- •Reduced power during acceleration
Likely Causes
Cracked vacuum lines, a leaking intake manifold gasket, or disconnected hoses on the Bank 2 side introduce unmetered air, causing a lean reading.
The heated oxygen sensor on Bank 2 may be worn, contaminated with oil or coolant, or electrically sluggish.
Clogged or leaking fuel injectors on the Bank 2 cylinders can reduce fuel delivery to that bank specifically.
A crack or leak in the exhaust manifold on Bank 2 can draw in outside air, fooling the oxygen sensor into reading lean.
Estimated Cost
Professional Repair
Includes parts + labor
Common Fixes
- Inspect and repair vacuum leaks on the Bank 2 side of the engine
- Replace the Bank 2 upstream heated oxygen sensor
- Clean or replace fuel injectors on Bank 2 cylinders
- Repair any exhaust leaks upstream of the Bank 2 O2 sensor