Put the code in context before ordering anything
Insufficient or excessive flow
Provide the code number rather than just the translated word EGR. Include the other records and whether the tool labels each as active, pending or historical.
Warnings and engine behaviour
Describe any change in idle, power or starting and the circumstances already observed. Those symptoms alone do not establish valve position or mechanical condition.
Previous work
If a valve has already been replaced, intake work carried out or codes erased, provide the record and sequence of events. A returning code is not proof that a new part is defective.
A flow-related record is not a component inspection
EGR returns some exhaust gas to the combustion process. HELLA describes different control arrangements and the relevance of other components that affect how the system is evaluated. A flow-related record therefore cannot be treated as a direct mechanical inspection of one valve. The underlying system and the information used to assess it both matter.
Depending on the design, an appropriate investigation may consider passage restrictions, control operation and related measurement. That is not a shopping list or a claim that every engine has the same vacuum hoses or sensor. An internet account involving a similar model cannot replace the correct engine documentation. A live-data number also needs units and operating context before it can inform a decision.
Preserve evidence before the warning is switched off
Save the available report, date and mileage before another intervention. Include operating information captured when the fault occurred if you already have it. You do not need to buy a scan application or reproduce the fault to prepare an enquiry. If you only have a verbal description from another garage, identify it as such rather than guessing missing code numbers.
Erasing a warning does not repair its cause and can remove useful context. OBD monitor readiness also matters before an emissions inspection; a separate guide covers that issue. Do not commission warning-light erasure as a substitute for investigating the fault. After repair, a single empty fault screen immediately following a reset is likewise not sufficient evidence that the original problem has been resolved.
Should EGR cleaning be booked straight away?
Cleaning, repairing a control issue and replacing a component are different proposals. Ask what supports each option and what outcome will be checked. Deposits are one relevant possibility, not a confirmed explanation for every P0401. Equally, P0402 does not by itself establish that a valve is permanently open and should simply be replaced.
Do not disconnect hoses or electrical connectors with the engine running, or spray cleaner into the intake as an experiment based on a generic video. An unsuitable intervention can complicate the subsequent assessment. An enquiry first establishes what can appropriately be checked on this vehicle. This guide does not promise universal EGR cleaning, engine decarbonisation or adaptation procedures across every make.
Request an agreed assessment, not a guessed parts price
Ask for investigation of the cause of the known code. Agree the initial scope and charge, what basic code reading includes and the point at which further approval is required. If an engine requires a specialist test or work beyond the workshop's confirmed scope, that should be clear before commissioning it. This article is not a catalogue of every specialist operation available locally.
Any subsequent repair proposal should separate assessment, labour, parts and follow-up verification. An honest fixed repair price needs the engine and supporting findings, not just the code. Include the vehicle's condition and any dangerous symptoms in your initial discussion. Receiving an enquiry does not itself confirm an appointment, a particular repair or permission to drive the car to the workshop.
Your checklist before contacting the workshop
- Make, model, year, fuel type and exact engine if known.
- Complete P0401/P0402 and related code records, with their available status.
- Existing engine symptoms, warnings, date and mileage.
- Records of previous EGR or intake work and any code clearing.
Use existing observations. Email only relevant records taken while safely parked; the form does not accept attachments.
Frequently asked questions
Does P0401 prove that the valve is clogged?
No. It records insufficient flow. Deposits are one possibility, not a diagnosis without supporting context and inspection.
If EGR was already replaced, must the new part be faulty?
Not automatically. Provide the intervention history and establish what the current findings support. A returning code alone does not prove a defective replacement.
Is clearing the code enough before an emissions test?
It does not repair the cause and may change OBD monitor readiness. Agree suitable fault investigation and verification; an unlit warning is not an emissions-pass guarantee.
Agree the next step
Send Autoservis 1 the report and engine details to agree a suitable initial assessment. The workshop is at Unhošťská 92, Červený Újezd, serving Unhošť, Hostivice, Kladno and Prague-West. With dangerous symptoms, call first; an appointment is not permission to drive an unsafe car.
Discuss a P0401/P0402 assessmentSources and limits
Published 24 October 2026. Sources explain general principles, not a diagnosis of your vehicle. Follow the instructions for your particular car.