Diagnostic Services - Fermoy car mechanic

Diagnostic Services

Fermoy Garage

Diagnostic Services

So there’s something not quite right about the way your vehicle is driving, or you’ve got a warning light on your dashboard that was blinking at you yesterday and now is on steady.

Car errors - fix in Fermoy garage

 What do you do?


Hint: the answer is not to put a piece of electrical tape over the warning light and ignore it.

What makes a warning light come on?


Today’s vehicles are manufactured with complex inter-related systems. On-board computers continuously monitor
and store information concerning the performance of these systems. 

Diagnostic Services fermoy garage

A warning light comes on because the computer has sensed a signal from one of the systems or components that has gone outside of its normal operating range.

The computer then sends a signal to turn on the light to let you know something is wrong!


While warning lights can go on and the car still appears to be driving “fine”, ignoring some lights can lead to serious issues, such as engine damage or another component failure.

In some instances, ignoring warning lights can be a safety hazard. That’s why it is recommended to be safe (give yourself peace of mind) and have your car looked at by a certified professional as soon as possible.

How can FermoyGarage “diagnose” my problem?


At FermoyGarage, we have the tools, training, and technology to handle diagnostic issues such as a Check Engine light. Properly performing a complete diagnostic procedure normally includes the following steps:

1. RETRIEVE DATA – A full functioning scan tool is used to perform an onboard computer system analysis in order to retrieve the following:

  • Computer codes
  • Freeze frame data
  • Computer software version numbers
  • Critical sensor data and status information

NOTE: Merely “pulling codes” does not generally provide enough information to make an accurate diagnosis of the problem. Pulling codes is the initial step in the process by identifying the circuit or system that has illuminated the vehicle’s check engine light.

2. VERIFICATION TESTING – Verification tests determine if systems meet proper specifications.
These tests may include an analysis of:

  • Engine vacuum and backpressure
  • Mechanical and electrical engine timing
  • Ignition system
  • Fuel system
  • Emissions system

NOTE: Failure in any of these basic systems can cause the check engine light to illuminate and falsely identify a circuit or component as the problem, which could lead to improper or unnecessary parts replacement.

3. PINPOINT TESTING – All manufacturers require that circuit or component pinpoint testing is done in order to make an absolute diagnostic determination.

These actions involve:

  • Working through wiring diagrams
  • Performing electrical and/or mechanical tests
  • Performing bi-directional control tests
  • Visual inspections of suspect areas