“I just need a fault light turning off.” This is something we hear on a regular basis and unfortunately is not that simple. If a system has an intermittent fault on it then it can usually be reset and the ECU will extinguish the light until the fault next occurs, which could be milliseconds to weeks or months later.
“The scanner tells you which part to change.” Actually the scanner gives an indication to a particular circuit that misbehaves. Even in a simple circuit that could include: several metres of wire, numerous joins or connectors, a sensor or actuator or influence from an undetectable mechanical fault. For example, a leak in a manifold can cause an ECU to set a fault code for a Manifold Absolute Pressure sensor outside limits.
“I bought a cheap EOBD reader on the internet but it won’t show the fault.” Whilst plain EOBD readers are great, we have three different “cheap” readers that we use for various things, they lack the software to access systems not covered by the requirements of EOBD. Enter several thousand pounds worth of equipment backed up by teams of developers constantly creating updates and new systems access for ever more complex vehicles.