What does P1157 mean on a Ford?

P1157. Lack of O2 Switches - Bank 2 Sensor 2 Lean. Applies to F-150, Mustang, Expedition.

What causes P1157 on a Ford?

Exhaust leak ahead of the bank 2 downstream sensor Aging downstream sensor stuck lean Failed converter on bank 2 Upstream lean fault carrying through Heater fault keeping the sensor cold

How do I fix P1157 on a Ford?

Smoke test the bank 2 exhaust Verify sensor heater operation Fix upstream fuel faults first Evaluate converter function Replace the downstream sensor after excluding leaks

Code

P1157

Lack of O2 Switches - Bank 2 Sensor 2 Lean

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

Findings, check these first

Exhaust leak ahead of the bank 2 downstream sensor
Aging downstream sensor stuck lean
Failed converter on bank 2
Upstream lean fault carrying through
Heater fault keeping the sensor cold

Standard procedure

Smoke test the bank 2 exhaust
Verify sensor heater operation
Fix upstream fuel faults first
Evaluate converter function
Replace the downstream sensor after excluding leaks

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

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OBDII.pro: P1157 Ford definition
live reference page (obdii.pro)
Supports: Ford-family meaning for P1157: Lack Of HO2S22 Switch - Sensor Indicates Lean
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Last updated 2026-09-05.

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