P2243: Bank 1 front oxygen reference-voltage circuit is diagnosed open

P2243 describes an open reference-voltage signal circuit for bank 1 sensor 1 in the reviewed GM wide-range oxygen-sensor system. An interface chip diagnoses the circuit and sends fault information to the ECM, which then applies its own counters.

Do not merge the interface variants

For the ATIC142 interface, an open indication can arise from an open reference-voltage pin or reference-cell voltage above 1.2 V while pump-cell voltage remains below 1.2 V. The internal qualification uses passive and active stages totaling 2.5 seconds.

A separate CJ136 variant uses deviation of the Nernst signal from 0.45 V by more than 1 V, with its own short internal qualification. These are alternative hardware strategies, not two tests that necessarily apply to the same vehicle.

Prerequisites are part of the diagnosis

The ECM requires 20 failures out of 24 at 25-millisecond sampling. The interface must be ready and measurements valid. Engine run or auto-stop status, completed heater warm-up and a subsequent delay exceeding 20 seconds are also required, with the listed heater and bank-level faults absent.

An early warm-up signal therefore cannot be interpreted against the enabled open-circuit decision without context. The code also does not simply mean that exhaust oxygen concentration is wrong.

Identify the actual sensor/interface system, then follow its electrical diagnostic procedure. Verification requires valid reference-circuit behavior and monitor completion. The source provides Type B, two-trip classification, but no universal pinout or replacement instruction.

Source and applicability

The documented system and calibration must be confirmed for the vehicle before using these limits. GM diagnostic table, PDF page 623.