Code Definition

P1128 — Upstream Heated O2 Sensors Swapped

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

About P1128

P1128 is a manufacturer-specific powertrain diagnostic trouble code recorded for Jaguar 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

On Jaguar vehicles, the P1128 fault code indicates the Engine Control Module (ECM) has determined that the upstream (Sensor 1) heated oxygen sensor signals for Bank 1 and Bank 2 appear to be swapped. The ECM detects this when it makes a fuelling correction to one bank and sees the oxygen sensor on the opposite bank respond, which shows the sensor inputs or their wiring are crossed. This most often follows recent work on the exhaust, sensors, or engine wiring where the two upstream sensor connectors have been interchanged. When this code is set the engine may run with incorrect fuel trims on ea...

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

Quick Facts