P2626: Front oxygen-sensor pump-current trim circuit fails its interface test

P2626 is a bank 1 sensor 1 trim-circuit diagnosis in the reviewed GM wide-range oxygen-sensor system. The trim circuit fine-tunes the pump-current signal; it is not the same circuit diagnosis as an open main pump-current path.

Interface and sensor type change the limits

The ATIC142 implementation identifies an open trim circuit using sensor-dependent resistance limits. For the selected NGK sensor type the listed upper limit is 4,644 ohms; a different Bosch sensor has a different boundary.

The CJ136 implementation instead gives a permitted NGK resistance region bounded by 118 ohms and 4 kilohms, with separate Bosch limits. It also requires that the pump-current circuit is not already detected open. These alternatives should never be combined into one universal sensor test.

A qualified intrusive test

The source associates the test with a run/crank transition from false to true, but it also requires subsequent eligibility: closed-loop fuel control, no off-stoichiometric mode, no deceleration fuel cutoff, pump current below 1 mA and the specified post-warm-up delay. Listed heater and bank-level faults must be absent.

One failed qualified sample can establish the monitor result, sampled on a 25-millisecond loop, although the DTC response is Type B, two trips. A key cycle alone therefore does not prove the test ran under all required conditions.

Verification should identify the actual sensor/interface combination, confirm valid trim-circuit behavior and allow the qualified diagnostic to complete. The source does not provide a replacement-part decision or a universal resistance-testing procedure.

Source and applicability

These limits describe the stated monitor and require vehicle, hardware and calibration confirmation. GM diagnostic table, PDF page 663. GM diagnostic table, PDF page 664.