What does P1151 mean on a Ford?

P1151. Lack of Upstream HO2S Switch - Sensor Indicates Lean (Bank 2). Applies to F-150, Mustang, Explorer, Expedition with V6 and V8 engines.

What causes P1151 on a Ford?

Vacuum leak affecting the bank 2 side of the intake Aging bank 2 upstream oxygen sensor stuck lean Low fuel pressure or restricted fuel delivery Dirty mass air flow sensor Exhaust leak ahead of the bank 2 upstream sensor

How do I fix P1151 on a Ford?

Compare bank 1 and bank 2 fuel trims to isolate the affected side Smoke test the intake for leaks near bank 2 runners Verify fuel pressure and MAF readings with a scan tool Inspect the exhaust manifold and pipes ahead of the bank 2 sensor Replace the bank 2 upstream HO2S after confirming fuel and air delivery

Code

P1151

Lack of Upstream HO2S Switch - Sensor Indicates Lean (Bank 2)

Category: Powertrain - Fuel/Air Metering
Severity: Check Engine Light
Applies to: F-150, Mustang, Explorer, Expedition with V6 and V8 engines
Related: P0174 System Too Lean (Bank 2) on OBD Codes List

Findings, check these first

Vacuum leak affecting the bank 2 side of the intake
Aging bank 2 upstream oxygen sensor stuck lean
Low fuel pressure or restricted fuel delivery
Dirty mass air flow sensor
Exhaust leak ahead of the bank 2 upstream sensor

Standard procedure

Compare bank 1 and bank 2 fuel trims to isolate the affected side
Smoke test the intake for leaks near bank 2 runners
Verify fuel pressure and MAF readings with a scan tool
Inspect the exhaust manifold and pipes ahead of the bank 2 sensor
Replace the bank 2 upstream HO2S after confirming fuel and air delivery

Code lookup

Type a code above, or start from a symptom or a common code.

Press / to jump to the box. Ford-enhanced powertrain, body, chassis and network codes. Generic P0xxx codes live on OBD Codes List.

Sources and review

Review: checked against the recorded source material.

OBDII.pro: P1151 Ford definition
live reference page (obdii.pro)
Supports: Ford-family meaning for P1151: Lack Of HO2S21 Switch - Sensor Indicates Lean
Fetched directly. obdii.pro is a publisher independent of the engine-codes family.
P1151 FORD Code: Meaning, Causes, and Symptoms | OBD2 Codes
live reference page (obd2-codes.co)
Supports: Ford meaning for P1151: Lack of Upstream Heated Oxygen Sensor Switch Sensor Indicates Lean Bank 2
Fetched directly. obd2-codes.co phrasing matches the engine-codes family, so it counts as one publisher.

Last updated 2026-09-04.

Report a correction for P1151. Include your vehicle, the issue and a source if you have one.

This fault is part of the Ford fuel and ignition codes guide. It covers the family and the order to check it.