P206B: reductant quality data remains unavailable when it should be ready

P206B is not, in this GM strategy, a direct judgment that DEF concentration is wrong. It checks whether the ultrasonic quality sensor fails to provide a ready measurement when conditions should permit one. The sensor reports low confidence through a readiness bit when its echo is weak, missing or inconsistent.

Eligibility separates unavailable data from bad fluid

The malfunction is the quality-readiness bit remaining false. The test requires more than 300 seconds since refill or draining, estimated DEF quantity above five liters, tank temperature between 0°C and 70°C, and UTLC temperature above 3°C. Heater 1 and heater 3 commands must be zero.

The table also requires no slosh flag, an active tank-agitation flag and vehicle speed above 2 km/h. Those apparently different movement flags should be kept distinct; the source does not say that any tank movement automatically invalidates the test.

Confirmation needs the same measurement opportunity

Relevant voltage, SENT communication and controller-internal faults must be absent. Failure qualification is 600 samples at 0.1 second, or 60 seconds; the listed success count is 40 samples. Reporting is Type A over one trip.

Verification should show the readiness bit becoming valid during a qualified measurement opportunity. A concentration number displayed while readiness is false is not equivalent evidence. Conversely, no fault immediately after refilling does not establish a pass because the waiting condition remains relevant. This monitor does not identify contaminated fluid or mandate sensor replacement. Exact vehicle and calibration applicability require confirmation beyond this 2025 GM summary.

Source: GM monitor, PDF page 191.