10 diagnostic jobs that might surprise you

With cars fast becoming computers on wheels, parts that were once simple remove and refit jobs, may now require reprogramming or adapting after installation. Failure to teach the new part how to behave using a diagnostic tool can cause the vehicle to exhibit the same fault as before, generate an entirely new fault or simply not perform as it should – be it higher emissions, lower fuel economy, poor engine performance or reduced safety. Either way, the chances are you’ll have a repeat visit from an unhappy customer, losing you time, money and potentially your reputation. So, to avoid any unwanted surprises, we asked our in-field service team for 10 diagnostic jobs that can catch even the most experienced technicians unawares.

With cars fast becoming computers on wheels, parts that were once simple remove and refit jobs, may now require reprogramming or adapting after installation. Failure to teach the new part how to behave using a diagnostic tool can cause the vehicle to exhibit the same fault as before, generate an entirely new fault or simply not perform as it should – be it higher emissions, lower fuel economy, poor engine performance or reduced safety. Either way, the chances are you’ll have a repeat visit from an unhappy customer, losing you time, money and potentially your reputation. So, to avoid any unwanted surprises, we asked our in-field service team for 10 diagnostic jobs that can catch even the most experienced technicians unawares.

1. When fitting a new air filter on some diesel powered Mercedes-Benz vehicles i.e. 2013 Sprinter 2.2L, a diagnostic procedure is required to tell the ECU that it has been replaced.  This then adapts the MAF sensor readings to ensure the correct air flow measurement is calculated.
2. Replacing a modern stop-start battery can take significantly longer than a conventional battery, because the vehicle’s energy management system must now be reprogrammed using a diagnostic device. If this is not performed, the stop-start system may not function correctly, resulting in increased fuel consumption and emissions. 
3. After replacing an EGR valve, on a Ford Focus 1.6TDi 2011 for example, the valve must be readapted. If not, the pintle can break off and drop into the engine, causing repeated EGR failures, and potentially catastrophic engine failure.
4. When installing air suspension springs on some BMW models, such as the 5 Series, a three-stage diagnostic process must be performed.  Failure to carry out these exact steps, in the right order, may result in the car sitting at different heights front to rear, or side to side, after replacement.
5. Windshield replacement is no longer a straight-forward job. On vehicles fitted with Advanced Driver Assistance Systems, otherwise known as ADAS, technicians will need to perform either a static or dynamic calibration to ensure these safety-critical systems still function correctly.

1. When a camshaft sensor, measuring both speed and position, is replaced on a Citroën C4 1.6D for instance, a diagnostic procedure is required to clear the learned values from the old sensor, and place the ECU into learning mode for the new sensor. Without this the vehicle owner may experience loss of power and poor fuel economy.
2. Even something as simple as a basic oil and filter change may now require a diagnostic procedure. Take a Volvo S60 1.6 gasoline - the ECU must now be reset to reflect the ‘oil quality’ values of the newly replaced oil.   
3. When changing brake fluid in an electronically controlled ABS system, a diagnostic tool is required to initiate a routine on the ABS ECU. By rapidly opening and closing the valves during the bleeding process, it ensures the air is purged from the modulator. Not doing this will result in the brakes not performing as they should.
4. Just to maintain the warranty on some electric vehicles, a battery health check must be performed using a diagnostic tool. This will measure the battery’s State of Health i.e. how much life it has left.
5. When fitting a new control arm on a vehicle equipped with self-leveling headlights, the sensor must be reset using a scan tool, to ensure the headlights are always at the appropriate height for the vehicle. Failure to do this could result in a vehicle with incorrect beams, reducing visibility for the driver and distracting oncoming vehicles.

These are just a few of many examples. There any many, many more. That's why it pays to keep up to date on your training, and we're here to help. For more information and to book a course please visit our training information page.