What does it mean?
P1622 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: O2 Sensor Reference Voltage Circuit High .
Symptoms
- MIL (check engine lamp) on
- Fuel trims swing widely, with the engine running rich or lean
- Rough idle, hesitation and poor throttle response
- Increased fuel consumption and a strong fuel smell from the exhaust
- Black smoke under load in bad cases
- Catalyst efficiency codes appearing later if the condition is left uncorrected
Likely causes
- Sensor signal or reference wire shorted to a voltage source in the harness
- Chafed insulation where the sensor loom runs close to the exhaust, the heater feed or a power wire
- Water and corrosion inside the sensor connector bridging the pins
- Sensor failed internally and pulling the circuit high
- Open or high-resistance sensor ground, which makes the signal read high
- Incorrect or generic replacement sensor with a different wiring arrangement
- Module reference circuit fault, the least likely cause
How to fix it
- Read live data and see whether the sensor voltage sits pegged high and refuses to react when the mixture is deliberately changed
- Unplug the sensor and measure the signal and reference wires with the ignition on; neither should sit at battery voltage
- Trace the sensor harness for chafing, especially near the exhaust and where the loom crosses the engine or the bulkhead
- Test the sensor ground for continuity and voltage drop, and check the heater circuit separately
- Confirm the fitted sensor is the correct type and correctly wired if it has been replaced before
- Repair the short or replace the sensor, then clear the codes and verify the sensor switches normally through a drive cycle
- Consider the module reference circuit only after the harness and sensor are proven good