U05A3 Moderate Generic / SAE

U05A3: Invalid Data Received From Reductant Quality Module

Network and Communication Invalid Data Received (continued) Emissions related

What to do

Say exactly what went into the tank and when. This is the code that is often telling the truth — water, screenwash, diesel, or exhaust fluid from a container that has been open for a year all genuinely fail the test, and the fix is draining and refilling rather than a part.

If this appeared in a hard frost, mention that. Exhaust fluid freezes at around minus eleven degrees, and a partly frozen tank cannot be measured. If it clears once the car has warmed through, the tank heater is the thing to look at, not the sensor.

Buy exhaust fluid in sealed containers and use it reasonably promptly. It has a genuine shelf life, and heat shortens it.

Do not ignore it because the car drives normally. Like the other exhaust fluid faults, this one escalates on a schedule — warnings, then a speed limit, then a car that will not restart.

What this code means

The module measuring the quality of the exhaust fluid is reporting a value that cannot be accepted. See U0400 for the family's framing.

What this sensor actually measures is worth knowing, because it explains most of the false alarms. Exhaust fluid is a precise mixture — 32.5% urea in demineralised water — and the concentration matters: too weak and there is not enough ammonia to convert the nitrogen oxides, too strong and it crystallises in the injector. The sensor infers concentration from the speed of sound through the fluid, or from its dielectric constant, alongside its temperature.

Both methods are sensitive to temperature, and exhaust fluid freezes at about minus eleven degrees. A tank that is partly frozen is not a uniform liquid, so the reading is meaningless until it thaws — which is why these faults appear on the first hard frost and disappear by lunchtime. The system is designed for this and has a tank heater; a failed heater turns a winter inconvenience into a standing fault.

The second explanation is the honest one, and it is common. The sensor may be right. A tank topped up with water, with screenwash, with diesel, or with fluid that has sat in an open container for a year genuinely is not exhaust fluid any more — and the sensor is doing exactly its job. Exhaust fluid also has a real shelf life, shortened by heat, and a vehicle that stands for long periods can be running on fluid that has degraded in the tank.

Treat this as a fluid question before treating it as an electrical one. The order that costs nothing: what went in, when, and from what container — then the temperature history, then the heater, then the sensor.

And the consequence is the inducement ladder, as at U010E. A vehicle that cannot verify its fluid is treated as a vehicle that is not dosing, so the warnings escalate on a schedule regardless of how well it drives.

Likely causes

Start here

Reductant diluted or incorrect fluid · easy
Frozen reductant in the tank or lines · easy
Faulty reductant quality sensor · moderate

Less common

Reductant fluid past its shelf life · easy
Faulty reductant tank heater · moderate
Corroded or loose connector · easy

Symptoms

Components involved

Information, not instruction

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Have anything you intend to act on checked by a trained person against the manufacturer's own procedure for your vehicle. Nothing here replaces that procedure.

Community experience

Be the first to write this up

Nothing posted about this yet. Whatever you found is worth writing down — even a dead end saves someone the same afternoon.

What makes one worth reading:

The car — make, model, year and engine. The same fault behaves differently on each.
What you measured, not only what you replaced.
What actually fixed it — or that nothing did, which is worth knowing too.