Code Definition

P1128 — Upstream Heated O2 Sensors Swapped

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

About P1128

P1128 is a manufacturer-specific powertrain diagnostic trouble code recorded for Peugeot vehicles. It belongs to the P-prefix family of codes, which covers engine, transmission, emissions, or fuel-system faults.

When P1128 is stored, the module has detected 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.

P1128 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 fault code is set when the Engine Control Module (ECM) detects that the upstream (pre-catalytic converter) oxygen sensors have been installed incorrectly or their wiring is crossed. The ECM relies on these sensors for accurate air-fuel ratio adjustments. Incorrect sensor placement can lead to improper fuel mixture control, increased emissions, and drivability issues.

Quick Facts