Code Definition

P1143 — Heated Oxygen Sensor 1 bank 1 voltage low

System: Powertrain  |  Type: Manufacturer-Specific  |  Make: Infiniti

About P1143

P1143 is a manufacturer-specific powertrain diagnostic trouble code recorded for Infiniti vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1143 is stored, the module has detected a signal or supply voltage lower than the expected operating range; a bank-specific fault, meaning it applies only to one cylinder bank of a multi-bank engine; and a sensor-related fault — the reported value from the named sensor is out of spec.

Scanning & clearing: A generic OBD-II scan tool will usually read and clear powertrain (P) codes. For live data, freeze-frame capture, and bi-directional tests you may need a more capable scan tool that supports the vehicle's ECM protocol.

P1143 is a manufacturer-specific code. The same code string on a different make may have a different meaning. Always confirm the code's definition against the vehicle's service information for the specific make and model under test.

Code Information

The heated oxygen sensor 1 on bank 1 is the front, pre catalyst sensor that the Engine Control Module (ECM) uses to measure exhaust oxygen content and control fuel trim on the bank containing cylinder number one. DTC P1143 sets when the ECM detects that this sensor signal is biased low, meaning the voltage stays toward the lean end of its range and does not switch normally. This can be caused by a genuinely lean exhaust, by a contaminated or aged sensor, or by a fault in the sensor signal or heater circuit. Symptoms can include rough running, hesitation, increased emissions and reduced fuel ec...

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