What does fault code P1131 mean?

Lack of HO2S Switch, Sensor Indicates Lean (Bank 1 Sensor 1). Ford-specific code for the upstream O2 sensor not switching properly and reading persistently lean.

P1131

Lack of HO2S Switch, Sensor Indicates Lean (Bank 1 Sensor 1)

Q: What are the symptoms of P1131?

CEL; Possible rough idle or hesitation; Reduced fuel economy

Q: What are the possible causes of P1131?

Vacuum leak; Failing upstream O2 sensor; Exhaust leak before the sensor; Fuel delivery issue

Q: How to fix P1131?

Inspect for vacuum/exhaust leaks; Test O2 sensor response; Check fuel pressure; Replace sensor if others check out

Severity: Medium Fuel & Air Metering Ford Specific Est. Repair: $100 - $350

Schedule diagnosis soon. Continued driving may worsen the issue.

Quick Answer

P1131 means “Lack of HO2S Switch, Sensor Indicates Lean (Bank 1 Sensor 1).” Severity: Medium. Estimated repair cost: $100 - $350. Most common sign: CEL.

What Does P1131 Mean?

Ford-specific code for the upstream O2 sensor not switching properly and reading persistently lean.

Common Symptoms

CEL

Possible rough idle or hesitation

Reduced fuel economy

Possible Causes

Vacuum leak

Failing upstream O2 sensor

Exhaust leak before the sensor

Fuel delivery issue

How to Fix P1131 – Repair Guide

Inspect for vacuum/exhaust leaks

Test O2 sensor response

Check fuel pressure

Replace sensor if others check out

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Budgeting for This Repair?

A typical P1131 repair runs about $100 - $350. If you'd rather spread the cost over time, estimate the payment with our free sister tool: Car Finance Calculator (50-state sales tax, trade-in equity, full amortization).

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Disclaimer: Information is for educational reference only and does not replace professional diagnosis. Actual causes and costs vary by vehicle make, model, year and condition. Always verify with a qualified technician.