P206C: quality-sensor circuit low combines measurement and piezo faults

P206C is a reductant quality-sensor circuit-low code. The reviewed GM controller can receive it through two kinds of evidence from the smart UTLC sensor: an out-of-range quality measurement or internal piezoelectric sensing faults. The word “low” is therefore not a complete description of every trigger.

Distinguish the branches

One branch requires a quality measurement below 0% together with a true quality-readiness bit. A negative out-of-range result is not the same as a valid measurement showing slightly diluted DEF. Other branches include excitation voltage above 5.5 volts or below 4.5 volts and piezo voltage above 2.0 volts or below 0.125 volt.

Those piezo conditions are represented by one internal diagnosis bit sent over SENT. The code does not reveal which internal voltage condition occurred. The printed voltages also do not identify externally accessible test terminals.

When the controller accepts the result

An active vehicle power mode is required, and relevant SENT communication and controller-internal faults must be absent. Four failing half-second samples qualify the two-second condition; reporting is Type A over one trip.

Verification should establish valid communication and determine whether the fault originated from a ready out-of-range measurement or the internal electrical-status branch. Simply replacing fluid or reading a concentration display does not demonstrate that both paths are healthy. The source supplies no replacement instruction or broad vehicle coverage; the actual UTLC system and service procedure must be confirmed for the vehicle.

Source: GM monitor, PDF page 192.