Code Definition

P1155 — A/C Evap Temperature Switch High Voltage, or O2 Sensor Reading Lean (Bank 2 Sensor 1)

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

About P1155

P1155 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 P1155 is stored, the module has detected a signal or supply voltage higher 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.

P1155 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 has two platform dependent definitions, an A/C evaporator temperature sensor or switch reading high voltage, or the Bank 2 Sensor 1 upstream oxygen sensor reading lean. In the oxygen sensor form, P1155 sets when the PCM sees the Bank 2 upstream sensor biased toward lean, staying low in voltage and failing to swing rich during closed loop, which can reflect a genuine lean mixture on that bank or a skewed sensor. In the A/C form, the evaporator temperature sensor signal is high, which on a thermistor type sensor usually corresponds to a cold reading or an open c...

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