U010E: Lost Communication With Reductant Control Module
What to do
The car drives normally today, and that is the trap. A vehicle that cannot dose exhaust fluid is required by law to make the problem impossible to ignore, so expect a countdown: warnings first, then a mileage limit, then a reduced speed, and eventually a vehicle that will not restart once the count runs out.
So book this in promptly even though nothing feels wrong. The escalation runs on distance driven, and it does not pause because the car seems fine.
Ask for the connector and wiring at the exhaust fluid tank to be checked first. This module sits under the vehicle in road spray and salt, and a corroded connector there is far commoner than a failed module — which is an expensive part.
Topping up the AdBlue will not clear this. A low or contaminated tank sets different codes; this one means the module is not talking at all.
What this code means
The module that doses exhaust fluid into the exhaust has stopped being heard from. The family's framing is at U0100.
First, the names, because four of them mean one thing and the confusion is real. Reductant, diesel exhaust fluid, DEF, AdBlue and urea are the same fluid — a 32.5% urea solution injected into hot exhaust so that ammonia is released and the SCR catalyst can convert nitrogen oxides into nitrogen and water. A workshop system may call this module the DEF control unit and a scan tool may call it the reductant control module; nothing distinguishes them.
What makes this code more serious than its symptoms is that it starts a clock. A vehicle that cannot dose is a vehicle emitting more NOx than it is certified for, and the law requires it to make that impossible to ignore. So the response is not a warning light and a shrug — it is the inducement ladder, the same escalation the corpus describes in the P2Bxx range: messages, then a countdown of miles, then a speed limit, and finally a vehicle that will start a fixed number of times and then not at all.
Which means the useful thing to know is the order of events, not the fault. Today it drives normally. The consequence arrives on a schedule, and the schedule keeps running while the vehicle is used.
Where the fault usually is: the module lives on or beside the exhaust fluid tank, under the vehicle, in road spray and salt. Its connector is in one of the worst positions on the vehicle, and corrosion there is ordinary rather than exceptional. Check that and the supply before the module.
A tank that has been refilled with the wrong fluid, or with water, produces a different set of codes — the quality and level ones — not this one. This code is about silence on the network.
Likely causes
Start here
- Corroded or loose connector · easy
- Damaged wiring harness · moderate
- Failed power or earth supply to the module · moderate
Less common
- Damaged data bus wiring · moderate
- Water ingress into connector · easy
Symptoms
Components involved
Information, not instruction
CarGeek is a reference, not a service manual. Its pages are written from public sources and from what other people have found, never from a manufacturer's own service information, so they can be wrong or incomplete for your particular vehicle. Some of what they describe carries real risk: high voltage, fuel under pressure, stored energy, hot and moving parts.
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
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