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P1143 Manufacturer-specific Basic entry

Lack Of HO2S12 Switch - Sensor Indicates Rich

Updated 2026-10-02 · Manufacturer-specific powertrain

Severity
Medium
Typical repair cost
60 – 500 EUR
System
Powertrain

This is a manufacturer-specific code. Its exact meaning can differ between makes; the definition below follows the most common usage.

What it means

P1143 is defined as "Lack Of HO2S12 Switch - Sensor Indicates Rich". the engine control module stores it when the monitored condition for this component or system is outside the limits programmed by the manufacturer.

This entry is compiled automatically from the standard definition and typical diagnostic practice for this type of fault. A detailed, reviewed article is in preparation.

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Symptoms

  • Check engine light on
  • Rough or unstable idle
  • Hesitation or poor acceleration
  • Increased fuel consumption
  • Possible limp mode with reduced power

Common causes

  1. Lack Of HO2S12 Switch - Sensor Indicates Rich worn, contaminated or out of calibration
  2. Mechanical problem in the system the sensor measures
  3. Air, vacuum or exhaust leak influencing the reading
  4. Wrong or low-quality replacement part
  5. Wiring resistance causing a small voltage offset

How to diagnose

  1. Compare the live Lack Of HO2S12 Switch - Sensor Indicates Rich reading with a known-good value or a second sensor at idle and at 2500 rpm
  2. Check for air, vacuum or exhaust leaks that could skew the reading
  3. Inspect the component for contamination and clean it if the design allows
  4. Verify the part number is correct for the engine
  5. Replace the Lack Of HO2S12 Switch - Sensor Indicates Rich if the reading remains out of specification

Frequently asked questions

Can I keep driving with P1143?

Usually yes for a short time, but expect reduced performance or higher fuel use. Have it diagnosed within a few days.

Will clearing P1143 fix it?

No. Clearing only erases the stored code; it returns as soon as the monitor runs again unless the cause is repaired.

Related codes

P1141P1142P1144

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