P206A – Reductant quality sensor – malfunction

Bojan Popic
By Bojan Popic (Contact Me)
Last Updated 2022-11-24
Master Mechanical Engineer
CodeFault LocationProbable Cause
P206A Reductant quality sensor - malfunction
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Wiring, reductant quality sensor, ECM

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Table of Contents

  1. What Does Code P206A Mean?
  2. Where is the P206A sensor located?
  3. What are the common causes of code P206A?
  4. Get Help with P206A

What Does Code P206A Mean?

The generic description for the P206A error code is Reductant quality sensor – malfunction. To understand what this means, we must first explain what the reductant actually is and what it does. Most truck drivers and heavy-duty pickup truck owners probably know this is another name for Diesel Exhaust Fluid or DEF fluid.

This urea-based liquid gets injected into the stream of exhaust gases, reducing its NOx content. Simple as it may be, this system has several failure points, which may eventually prevent the vehicle from being started.

Where is the P206A sensor located?

In a diesel-powered vehicle, the DEF fluid, which is sometimes referred to as AdBlue, is stored in a separate tank. From there, an inbuilt pump transfers it through a series of hoses towards the nozzle fitted on the exhaust pipe. Once injected into it, this liquid reacts with NOx gasses, turning them into nitrogen and water.

The vehicle’s PCM controls the process, ensuring it happens only when certain conditions are met. This includes the outside temperature as well as those of exhaust gasses and engine running parameters. In addition, the quality of DEF fluid and its level is continuously monitored by a dedicated sensor. This is done to ensure sufficient amounts of this fluid are available and to prevent the drivers from driving without it.

In essence, the reductant quality sensor measures the temperature of the DEF fluid and compares it against the intake air and coolant temperatures. Depending on these temperature readings, the vehicle assesses if the fluid level is low or if its quality is inadequate. This, if it happens, will trigger a MIL warning light on the dashboard, and the P206A code will be stored in the diagnostic memory. Furthermore, the vehicle will go into Limp Home mode after a certain number of starts with DEF-related issues. Due to its task, the reductant quality sensor has to be installed within the DEF fluid tank, which most car makers install just next to the fuel tank.

What are the common causes of code P206A?

The P206A trouble code will appear when the signal from the reductant quality sensor is out of range. But before blaming this on the sensor itself, several other things should be checked.

Damaged or corroded connector
The first on the list is the wiring connector at the top of the DEF tank. This position makes it exposed to moisture and mud, which, if it finds its way into the connectors’ body, will cause corrosion on the pins. In addition, the connector itself may be cracked or loose. Both situations will cause interference with the reductant quality sensor’s signal, making it appear as if it is faulty.

Broken wiring
Like connectors, the wiring that goes from the vehicle toward the DEF tank may be damaged. In most cases, this will be caused by mechanical force, such as when being hit with road debris, or rodents. Again, this may mess up the DEF sensor signal.

Malfunctioning IAT or Coolant temperature sensor
The values coming from the reductant quality sensor are compared with intake air and coolant temperatures. And if one of them is off, the vehicle’s PCM may interpret this as a DEF-related issue. Before changing the sensor, the values for intake air and coolant temperatures should be double-checked.

Defective reductant quality sensor
Lastly, if all of the above checks out, a faulty reductant quality sensor remains the only likely culprit. This can be verified with a multimeter, used to measure the voltage coming from it, depending on the actual temperature of the DEF fluid. However, the actual values are not the same for every manufacturer, which is why a service manual is needed for this step.

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