Code Definition

P1143 — O2 Sensor Reading Lean or Low Voltage (Bank 1 Sensor 3)

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

About P1143

P1143 is a manufacturer-specific powertrain diagnostic trouble code recorded for GM 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

This General Motors specific code applies to the Bank 1 Sensor 3 oxygen sensor, a third sensor used on vehicles that place an additional oxygen sensor further down the exhaust, typically after a second catalyst section. P1143 sets when the PCM sees the Sensor 3 signal biased toward lean, staying at a low voltage rather than reading the higher voltage expected from the exhaust at that point. Depending on the platform this sensor assists catalyst monitoring and fine fuel trim, so a low or lean reading suggests a contaminated or aged sensor, an exhaust leak drawing in air ahead of the sensor, or ...

Join TaT to view the complete code information and diagnostic details.

Quick Facts