Code
P206C
Generic
P — Powertrain
Reductant Quality Sensor Circuit Low
Views:
UK: 21
EN: 29
RU: 30
AI status
Completed
Completed
100%
Causes
- Failed reductant quality sensor (internal short or open)
- Broken, shorted or corroded wiring or connector in sensor circuit
- Poor or missing ground or reference voltage to sensor
- Contaminated or crystallized reductant (urea deposits) affecting sensor operation
- Intermittent connection from vibration or damaged connector seal
- Faulty control module (rare)
Symptoms
- MIL/Check Engine Light illuminated
- Reduced emissions system performance; possible limp mode in some systems
- Diagnostic trouble codes related to SCR/reductant system
- Possible difficulty with SCR dosing or regeneration events
- No obvious engine mechanical symptoms in many cases
What to check
- Read stored codes and freeze-frame/failed-state data with a scan tool
- Check live data for reductant quality sensor signal (voltage or resistance)
- Inspect sensor connector and wiring harness for damage, corrosion, loose pins
- Verify sensor reference voltage and ground at the connector with key ON (engine OFF)
- Measure continuity and resistance of the circuit back to the ECU; perform wiggle test
- Visually inspect reductant fluid level and condition for contamination or crystallization
Signal parameters
- Sensor type: typically analog voltage (0–5 V) or resistive output — consult vehicle-specific data
- Expected idle/normal output: commonly ~0.5–4.5 V depending on sensor design; 'Low' indicates near 0–0.5 V
- Reference supply: usually regulated 5 V reference from ECU (verify specific value)
- Ground: low resistance connection to ECU ground (< 1 ohm typical)
- Short to ground will pull signal toward 0 V; open circuit may float or read out-of-range
Diagnostic algorithm
- Retrieve all related codes and freeze-frame data. Note operating conditions when code set.
- Inspect visually: connector seals, pins, wire insulation for damage, corrosion, or urea deposits. Repair any obvious damage.
- With ignition ON (engine OFF), backprobe the sensor connector and verify reference voltage and ground presence at the connector. Record values.
- Measure the sensor output voltage (or resistance if applicable) with the connector connected and key ON/engine as required by the service manual. Compare to expected range.
- If output is low, disconnect the sensor and check for short to ground on the signal wire (measure continuity to chassis ground).
- Check continuity between sensor connector and ECU connector for signal, reference, and ground circuits. Repair any opens or high resistance.
- If wiring is good and proper reference/ground are present but output remains low, remove and inspect the sensor element for deposits or contamination. Clean only if permitted by OEM procedure; otherwise replace sensor.
- After repair or replacement, clear codes and perform a test drive or required relearn/initialization procedure. Re-scan to confirm code does not return.
- If fault persists with good wiring and new sensor, consider ECU diagnosis or replacement as a last step.
Likely causes
- Damaged or corroded connector / wiring causing low or lost signal
- Failed sensor due to internal fault or contamination
- Missing reference voltage or ground at sensor
- Urea crystallization or contamination on sensor element
Fault status
Status
Reductant quality sensor circuit voltage is below the expected range (low). This indicates the sensor output or wiring is reporting a low signal to the control module.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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