Fault code

P0401 fault code.

This code comes up with 2 known faults.

Generic code

Code type

Engine and drivetrain

System

Exhaust gas recirculation flow is insufficient

The EGR valve feeds exhaust gas back to the intake side so that less nitrogen oxide is formed. The engine control unit measured less of it than expected. A coked EGR valve, a clogged passage, a cracked EGR cooler or a faulty sensor all lead here.

The code tells you what the control unit measured, not which part has failed. The same code has several possible causes.

Which known faults it comes up with

EA189 TDI: EGR valve and particulate filter blocking

expensive

The EGR valve and its cooler block up with soot and oily deposits; the particulate filter cannot regenerate on short urban trips. The signs are reduced power, a warning light, and frequent regeneration. The software update after the diesel emissions affair made the EGR operate more often, which accelerated the phenomenon: the maker gave goodwill repairs in several cases.

between 140,000 and 160,000 km

What to check

Ask what kind of journeys the car did: a daily short urban run is the worst for the filter
With a code reader look at the stored faults (P0401/P0402, and P2002 for the filter)
Ask whether it received the post emissions affair software update, and when

1 more steps in the write-up

EGR valve and intake manifold: soot half blocks the channels

expensive

The EGR system recirculates the unburnt gases into the intake manifold, and together with the fumes from the crankcase breather this builds soot into the channels. The deposit gathers slowly, and by 150 000 kilometres the channels of the intake manifold can be as much as half blocked.

Show the rest

The symptom is jerking under acceleration, an uneven idle and occasional stalling. Codes P0401 and P0402 appear in the fault memory, and black smoke can come from the exhaust.

The solution is proper cleaning of the valve and the intake manifold. Deleting the EGR in software is not a solution: it does not remove the cause of the deposit, and it also affects the compliance of the vehicle.

At a purchase the kind of use is what matters: in a car driven on short urban journeys the soot gathers faster, because the engine does not warm up properly.

above 150,000 km

What to check

Accelerate hard: jerking and hesitation belong here
Watch the engine at idle: uneven running and occasional stalling are signs
Have the fault codes read and look for codes P0401 and P0402

3 more steps in the write-up

Information, not an expert opinion

We write the descriptions, and we put the source next to them. A person reviews them before they go out. They are still information, not a technical expert opinion.

A fault on the list does not mean the car you are looking at has it.
A fault missing from the list does not mean the model is fault-free. Write-ups are made model by model. Not all of them are done.
You decide whether to buy. This is no substitute for an inspection. That needs a workshop and a history check.

Details in the terms