P206B — Reductant Quality Sensor Circuit Range/Performance

Causes

• Faulty reductant quality sensor
• Damaged, corroded or disconnected sensor connector or wiring (open, short to ground, short to power)
• Contaminated, diluted or incorrect reductant fluid
• Low reductant (DEF/AdBlue) level allowing sensor exposure to air or crystals
• Faulty sensor heater or internal electronics
• Poor ground or supply voltage to the sensor

Symptoms

• Malfunction Indicator Lamp (MIL) or DEF warning illuminated
• Reduced power or limp mode depending on manufacturer strategy
• Reduced or inhibited SCR performance; possible increased NOx emissions
• DEF system warnings on cluster or message center
• Failed emissions/inspection tests

What to check

• Read freeze frame and live data with a capable scan tool; record reductant quality sensor values and related DEF system codes
• Visually inspect DEF tank, filler neck and sensor area for contamination, crystals or foreign material
• Inspect sensor wiring harness and connector for corrosion, damage, pin push-out or water intrusion
• Confirm DEF level and check for correct fluid (no water or improper fluids)
• Backprobe connector and check reference voltage (typically 5 V reference), signal voltage range and ground integrity
• Measure heater circuit resistance if applicable and compare to specification

Signal parameters

• Sensor uses vehicle reference voltage (commonly 5 V) and ground; signal typically within 0–5 V range depending on fluid condition
• Normal idle/steady values often near mid-scale; out-of-range low or high voltages indicate sensor or circuit issues
• Heater circuit (if present) generally measures in the tens to a few hundred ohms range (manufacturer-specific)
• Short to battery will show near battery voltage on signal; short to ground will show near 0 V
• Rapid or erratic signal fluctuations can indicate intermittent connection, contamination or failing sensor electronics

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