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P1646
ECM HO2 Sensor control malfunction – bank 1 upstream (1/1)
ECM HO2 Sensor control malfunction – bank 1 upstream (1/1)
Documented for: 2.0L gasoline; 2.5L/3.0L gasoline · System(s): EMS EOBD, EMS OBD II · Factory MIL flag: 2 · Default action: ECM Default: –HO2S 1/1 control circuit inhibited
Common causes
- HO2 Sensor 1/1 heater failure HO2 Sensor 1/1 sensing circuit: short circuit to ground
- short circuit to high voltage
- open circuit ECM Failure
- Fuel pump relay 2 - malfunction / HO2 Sensor Bank 1
- Linear O2 Sensor Control Chip (Bank 1)
Quick checks
- Confirm freeze-frame and conditions when the code set
- Inspect connectors, grounds, and harness for the circuit named in the code
- Compare live sensor values vs expected (unplugged/biased sensors are common)
Typical fixes
- Replace upstream O2 sensor Bank 1