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P1144

HO2S Bank 1 Sensor 3 Signal Above 0.45v AF Ratio Too Rich.

  • Mazda
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
1
AreaFuel and air metering
44
FaultThe specific fault in that area

What it means

On a Mazda, P1144 means the third heated oxygen sensor on bank 1 has been reading above about 0.45 volts, which the engine control unit interprets as a rich air/fuel mixture. Sensor 3 is normally the sensor downstream of the catalyst or catalysts, so the code can point to a rich exhaust condition, a sensor fault or a catalyst problem. Which sensor is 'sensor 3' depends on the model and exhaust layout.

Symptoms

  • Engine warning light on
  • Slight rise in fuel consumption
  • Smell of fuel or a sulphur-like odour from the exhaust
  • Rough idle or hesitation if a real rich condition exists
  • Possible failed emissions test

Possible causes

  • Genuine rich running from a fuel system fault such as a leaking or sticking injector or high fuel pressurepossible
  • Faulty or contaminated bank 1 sensor 3 oxygen sensor reading highlikely
  • Wiring or connector fault on the sensor circuit, such as a short to voltage or poor sensor groundpossible
  • Degraded or overloaded catalyst affecting the downstream readingpossible
  • Upstream sensor, air flow or coolant temperature sensor fault causing the mixture to run richpossible
  • Exhaust contamination from coolant or oil burningrare
  • Engine control unit faultrare

How to diagnose

  1. Read all stored and pending codes and the freeze frame data, noting engine temperature, load and fuel trim values at the time the code set.
  2. Check for other fuel trim, misfire, air flow or coolant temperature codes and deal with those first.
  3. Inspect the bank 1 sensor 3 wiring and connector for damage, heat or fluid contamination, corrosion and loose pins.
  4. Check the exhaust for leaks near the sensor, as these can distort readings.
  5. With a scan tool, watch live short and long term fuel trims and the upstream sensor readings to see whether the engine is really running rich.
  6. Watch the sensor 3 voltage live at operating temperature and see whether it stays high and fails to respond to mixture changes.
  7. Check the sensor heater circuit and the sensor's supply and signal wiring for resistance and shorts, following the manufacturer's data for your model.
  8. Check fuel pressure and inspect injectors and the air intake path if the trims show a rich condition.

How to fix

  • Repair any wiring or connector fault found on the sensor circuit.
  • Replace bank 1 sensor 3 if it is confirmed faulty or contaminated.
  • Correct the cause of any real rich condition, such as a leaking injector, high fuel pressure or a faulty air flow or temperature sensor.
  • Replace the catalyst if testing shows it is degraded, once the cause of the damage is fixed.
  • Repair any exhaust leak affecting the sensor reading, then clear the code and road test to confirm it stays away.

Can I keep driving?

Medium severity

The car can usually be driven for a short time, but book it in soon because a genuinely rich mixture wastes fuel and can damage the catalyst. If it runs badly or smells strongly of fuel, limit driving.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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