What does a Diagnose & Plan assessment cost?

We confirm the price of the assessment when you book, before any work starts. Any repair is priced separately in your written plan, and nothing is done without your written approval.

Is reading the fault codes the same as Diagnose & Plan?

No. A fault code shows where the car has noticed a problem, which is not always where the problem starts. We use the codes as a starting point, then test to prove the cause before we recommend a repair.

What if the cause needs more testing?

We tell you in writing what we have tested, what we found and what further testing is needed, with its price. We go further when you agree, not before.

Do I have to have the repair done with you?

No. The written plan is yours to keep, and you decide what happens next.

Which faults is Diagnose & Plan for?

Warning lights, misfires, intermittent faults and electrical faults. For a diesel particulate filter, AdBlue or EGR concern, or for an automatic gearbox, we also offer a DPF and emissions health check and a transmission condition check.

Fault assessment before any repair

Diagnose & Plan: find the cause, then decide

Diagnose & Plan is an initial specialist assessment of a fault: we test the car, find the cause and give you a written plan and price for the repair. Nothing is repaired until you have read the plan and given us your written approval.

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Last updated 12 November 2026

What is Diagnose & Plan?

Diagnose & Plan is an initial specialist assessment of a fault. We test the car, find the cause and give you a written plan and price for putting it right. You then decide what happens next.

A fault code is not a repair. A code shows where the car has noticed a problem, which is not always where the problem starts. So we test to prove the cause before we recommend any part.

Which faults is it for?

warning lights on the dashboard
misfires
intermittent faults that come and go
electrical faults

For a diesel particulate filter, AdBlue or EGR concern, see the DPF and emissions health check. For an automatic or dual-clutch gearbox, see the transmission condition check.

What does the assessment cover?

Your account of the fault. We ask when it happens, what you notice and what has been done about it before.
Fault memory. We read the stored fault codes and the data saved with them.
Testing. We carry out targeted tests on the system involved, such as live data readings and electrical checks, to find which part or connection has failed.
Road test. Where it is safe and useful, we drive the car to see the fault for ourselves.
Photos. We photograph what we find.

What do I get?

A written plan that sets out:

what we tested and what we found, with photos
the cause we have proved
the repair we recommend, with a written price
anything we could not yet confirm, and what further testing it would need

What happens next?

Send the enquiry form on this page and tell us about the fault.
We contact you to confirm a booking.
We carry out the assessment and give you the written plan and price.
You decide. Nothing is repaired until you give us your written approval.
If you go ahead, we carry out the repair, then test the car again to check the fault has gone.

What is not included?

the repair itself and any parts, which are priced in your plan
further testing beyond the initial assessment, which we price and agree with you first
recall work, which is done by the manufacturer’s network: check your car on gov.uk

For a general fault or warning light enquiry, see car diagnostics.

Our promise on every job

Written approval before any extra work
Photographic proof of what we find
A promised update time
No surprise invoice
A test drive and verification where appropriate

Our service centre

Where will my car be looked after?

At our centre at 57 Great North Road, Welwyn Garden City, built so that waiting for your car is not wasted time.

Seven ramps and an on-site MOT bay
Three customer waiting areas
A co-working space with Wi-Fi
A multi-faith prayer room and quiet room
Lavazza coffee
Customer parking

Questions people ask us

What does a Diagnose & Plan assessment cost?: We confirm the price of the assessment when you book, before any work starts. Any repair is priced separately in your written plan, and nothing is done without your written approval.
Is reading the fault codes the same as Diagnose & Plan?: No. A fault code shows where the car has noticed a problem, which is not always where the problem starts. We use the codes as a starting point, then test to prove the cause before we recommend a repair.
What if the cause needs more testing?: We tell you in writing what we have tested, what we found and what further testing is needed, with its price. We go further when you agree, not before.
Do I have to have the repair done with you?: No. The written plan is yours to keep, and you decide what happens next.
Which faults is Diagnose & Plan for?: Warning lights, misfires, intermittent faults and electrical faults. For a diesel particulate filter, AdBlue or EGR concern, or for an automatic gearbox, we also offer a DPF and emissions health check and a transmission condition check.