What does code P1128 mean on Mazda vehicles?
The ECU detects that the oxygen sensor signals are reversed during self-test.
OBD-II Code Mazda
P1128 — Mazda — HO2S Bank 1 Sensor 1 Signals Swapped in Key On Engine Running Self-Test
The ECU detects that the oxygen sensor signals are reversed during self-test.
Common symptoms
- Check engine light
Possible causes
- Miswired oxygen sensor connections
Initial recommendation
Verify oxygen sensor wiring and correct signal routing.
Safety notice
This information is for guidance only. Brand-specific codes may vary by model, year, engine, transmission and vehicle configuration. It does not replace a physical inspection or diagnosis by a qualified mechanic. If the vehicle is unsafe to operate, avoid driving it and seek professional inspection.
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