ECU & vehicle fault-finding guides
Communication faults, non-starts and sensor warnings need evidence from the whole vehicle. Plan the diagnostic handover before condemning a controller.
Plan the enquiry around the actual job.
Start with the complete scan and actual behaviour: whether the vehicle cranks, starts briefly, fails hot or loses communication intermittently. Include the reporting modules and the repairs already attempted. A code description is a starting point for investigation.
Vehicle supplies, grounds, wiring and connected systems can imitate a controller failure. These guides help owners gather useful details and garages share completed tests. They are planning references; electrical procedures and decisions still need to match the exact vehicle.
View the related service and its assessment process, or use the enquiry finder if you are unsure which route fits.
Read what helps your next step.
No communication with the ECU: why diagnosis comes before replacement
A missing diagnostic connection is a symptom. Find out which information helps distinguish a controller fault from a vehicle-side problem.
Read the guideLow or missing 5V reference: does the fault really need an ECU repair?
A reference-supply complaint needs the circuit and measurement context, as well as the controller. Build a useful diagnostic handover before replacing parts.
Read the guideIntermittent or hot non-start: the information that helps diagnose it
Record crank behaviour, temperature, communication and scan findings when a vehicle starts normally at some times but refuses at others.
Read the guideLost communication and U-codes: why the whole vehicle scan matters
Network warnings need the reporting modules, fault status and electrical findings. A code mentioning an ECU does not by itself prove that ECU failed.
Read the guideVAG P1570: starts then stalls after ECU replacement
For an applicable VAG system, P1570 needs a review of starting behaviour, controller matching and supply findings. Avoid assuming every non-start is immobiliser related.
Read the guideECU bench test passed, but the vehicle still has a fault: what next?
Understand the limits of a removed-unit assessment and prepare the vehicle evidence needed when an ECU fault cannot be reproduced on the bench.
Read the guideSuspected ECU damage after a jump start or electrical event
Prepare a clear electrical-event history, vehicle findings and controller details before choosing ECU repair, data recovery or replacement.
Read the guideThe ECU communicates, but an injector or actuator does not work
Communication alone does not establish the cause of an output fault. Share the affected circuit, load checks and diagnostic findings for assessment.
Read the guideEngine ECU or gearbox TCU fault? Start with the complete vehicle scan
Poor shifts and reduced performance can cross engine and transmission systems. Build an enquiry from the whole scan, behaviour and recent changes.
Read the guideAn ECU repair quote starts with a useful diagnostic report
Send a complete scan, failure-state observations and the checks already performed. A clear report helps separate suspected ECU failure from a wider vehicle fault.
Read the guideDiesel smoke after a remap: collect the evidence first
Describe new smoke, warnings and operating conditions after software or hardware changes. Diagnose the vehicle and review the history before requesting another calibration.
Read the guideAsk about your vehicle.
Send the registration, postcode and the evidence described in the relevant guide.