P223E: Oxygen reference-cell resistance implies an out-of-range temperature

P223E identifies an out-of-range oxygen-sensor reference-cell resistance in the reviewed GM monitor. The sensor interface reports element resistance, and the controller relates it to element temperature using the released sensor specification.

Temperature is inferred from electrical behavior

The documented malfunction limits are a measured reference-cell temperature below 700°C or above 1,000°C. These are sensor-element diagnostic values; they are not coolant-temperature limits or an exhaust-temperature specification for the vehicle.

The controller increments a failure count when the inferred temperature lies outside the expected range. It needs 128 failures out of 160 samples, taken every 25 milliseconds, for the documented decision. A brief value during a transition is different from a sustained out-of-range result in an enabled window.

Warm-up status changes the interpretation

The sensor interface must report valid measurements and ready status, with engine run or auto-stop active. Heater warm-up must be complete and the specified following diagnostic delay must exceed 20 seconds. Listed heater faults and the bank-level fault bundle must also be absent.

Consequently, a low inferred temperature immediately after starting is not enough to establish this diagnosis. Confirm that the warm-up and diagnostic conditions actually permitted the resistance check.

Verification should use the correct sensor data interpretation, confirm valid interface status and allow the monitor to complete after repair. The code does not directly prove a failed heater, an overheated engine or a particular replacement part. The source lists Type B, two-trip behavior for this calibration.

Source and applicability

The documented system and calibration must be confirmed for the vehicle before using these limits. GM diagnostic table, PDF page 622.