P1151 Lack of Upstream HO2S Switch - Sensor Indicates Lean (Bank 2)

What does P1151 mean on a Ford?

P1151 — Lack of Upstream HO2S Switch - Sensor Indicates Lean (Bank 2). This Ford-enhanced code applies to F-150, Mustang, Explorer, Expedition with V6 and V8 engines.

Common causes of P1151

• 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 to fix P1151

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