HO2S Bank 1 Sensor 1 Signals Swapped In Key On Engine Running Self Test
On Mazda vehicles, P1128 is logged when the ECU detects a fault in the O2 / lambda: “HO2S Bank 1 Sensor 1 Signals Swapped In Key On Engine Running Self Test”. P1128 is a manufacturer-specific Mazda code (the "1" after the letter marks an OEM-defined code), so its meaning applies to Mazda and may differ on other makes.
Typical triggers for a O2 / lambda code like P1128 include faulty or ageing sensors, wiring/connector faults, a clogged or removed component, or a value drifting outside the ECU's expected window. Symptoms range from a check-engine light only, to limp mode, rough running, higher consumption or failed emissions tests.
When a Mazda has had hardware changed for off-road/motorsport use (for example a removed DPF or EGR), the related monitor must be disabled in the ECU map or the code re-appears. Softechpro Solutions performs DPF/EGR/AdBlue/DTC off and recalculates the checksum, so codes like P1128 stay cleared after the flash. Genuine faults should always be repaired, not just hidden.
Softechpro Solutions does DPF/EGR/AdBlue/DTC off + checksum for 260+ ECU families — from €98.99/mo.
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