What does P1111 mean on a Ford?

P1111. Catalyst System Fault (Ford Enhanced). Applies to Mustang, F-150, Taurus with catalyst monitoring.

What causes P1111 on a Ford?

Degraded catalytic converter Failing downstream oxygen sensor Exhaust leak skewing the monitor Unresolved misfire damaging the catalyst Contaminated converter from coolant or oil burning

How do I fix P1111 on a Ford?

Compare upstream and downstream sensor activity Smoke test the exhaust for leaks Fix any misfire codes first Check for coolant or oil consumption Replace the converter after confirming sensor health

Code

P1111

Catalyst System Fault (Ford Enhanced)

Category: Powertrain - Auxiliary Emissions Controls
Severity: Check Engine Light
Applies to: Mustang, F-150, Taurus with catalyst monitoring
Related: P0420 Catalyst System Efficiency Below Threshold (Bank 1) on OBD Codes List

Findings, check these first

Degraded catalytic converter
Failing downstream oxygen sensor
Exhaust leak skewing the monitor
Unresolved misfire damaging the catalyst
Contaminated converter from coolant or oil burning

Standard procedure

Compare upstream and downstream sensor activity
Smoke test the exhaust for leaks
Fix any misfire codes first
Check for coolant or oil consumption
Replace the converter after confirming sensor health

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: qualified. Read the source limits below.

OBDII.pro: P1111 Ford definition
live reference page (obdii.pro)
Supports: Ford-family meaning for P1111: Intake Air Temperature (IAT) Sensor Circuit Intermittent High Voltage
Fetched directly. obdii.pro is a publisher independent of the engine-codes family.

Last updated 2026-09-05.

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