One of the biggest misconceptions about modern vehicle diagnostics is that finding a fault should be almost instant.
Plug in the diagnostic computer. Read the code. Replace the part.
Job done.
Sometimes a fault really is straightforward. But many vehicle problems are not.
Reading a fault code can take minutes. Diagnosing what caused that fault can take considerably longer.
At The Cape Brake Co, diagnostics is not simply about connecting a scanner to a vehicle. It is a process of gathering information, testing possibilities and following the evidence until we have a reasonable understanding of what is actually happening.
SCANNING AND DIAGNOSING ARE NOT THE SAME THING
A diagnostic scan is often one of the first steps in investigating a modern vehicle fault.
Professional diagnostic equipment can communicate with supported control modules and retrieve information such as:
- Diagnostic Trouble Codes
- Live vehicle data
- System information
- Stored fault information
- Data from different electronic control systems
That can give us an extremely useful starting point.
But the scanner cannot always tell us why a particular condition exists.
That is where fault finding begins.
WHY DOESN'T THE COMPUTER JUST TELL YOU WHAT'S BROKEN?
Because the vehicle can only report what its systems are detecting.
Imagine a control module receives a signal from a sensor that is outside the expected range.
The vehicle may recognise that the signal is wrong and store a fault code relating to that circuit or sensor.
But several things could potentially have caused the abnormal signal.
The sensor itself may have failed.
There could be damaged wiring.
A connector could have a poor connection.
The sensor may not be receiving the correct power supply or ground.
Or another problem may be causing the sensor to report a value that genuinely is outside the normal range.
The scanner has identified the symptom detected by the control system.
A technician still needs to investigate the cause.
SOME FAULTS ARE EASIER TO FIND THAN OTHERS
Not every diagnostic job takes hours.
Sometimes the evidence points towards a problem relatively quickly and testing confirms it.
Other faults require considerably more investigation.
The amount of diagnostic time required can depend on factors such as:
- The complexity of the vehicle
- The system involved
- How much technical information is available
- Whether the fault is currently present
- Whether several systems are affected
- Whether previous repairs have been attempted
- The accessibility of wiring and components
- Whether the problem is mechanical, electrical or a combination of both
There isn't a universal amount of time that every diagnostic problem should take.
INTERMITTENT FAULTS CAN BE PARTICULARLY DIFFICULT
One of the hardest faults to diagnose is often the one that isn't happening when the vehicle arrives at the workshop.
You may experience a warning light every few days.
The vehicle may occasionally refuse to start.
It might lose power only when hot.
An electrical system might stop working over bumps and then suddenly start working again.
By the time the vehicle reaches the workshop, everything may appear completely normal.
That doesn't mean the customer imagined the problem.
It means we need to work with the evidence that is available.
HOW DO YOU DIAGNOSE AN INTERMITTENT PROBLEM?
Depending on the fault, technicians may look at stored diagnostic information, inspect wiring and connectors, analyse live data or attempt to reproduce the conditions under which the problem occurs.
This is also why the information provided by the driver can be so valuable.
Knowing that a fault occurs:
only when cold
is very different from:
only after driving for 30 minutes.
Likewise, a fault that happens only under hard acceleration gives us different information from one that occurs while idling.
The more accurately the conditions can be described, the better the starting point for the investigation.
LIVE DATA CAN HELP US SEE WHAT THE VEHICLE IS DOING
Modern diagnostic equipment can often display information being reported by the vehicle in real time.
This is known as live data.
Instead of looking only at a stored code, we may be able to observe how sensors and systems behave while the vehicle is operating.
A technician can then compare those readings with the symptoms and expected behaviour of the system.
Sometimes that points towards the next test.
Sometimes it rules something out.
Both are useful.
Good diagnostics isn't only about proving what is wrong. It is also about eliminating what isn't.
ELECTRICAL TESTING TAKES THE INVESTIGATION FURTHER
If the evidence points towards an electrical problem, a scanner may not be enough.
The next step can involve physically testing the circuit.
Depending on the system, this might include checking:
- Power supplies
- Grounds
- Wiring continuity
- Connections
- Sensor signals
- Voltage
- Circuit behaviour
- Relevant components
A wiring diagram and appropriate technical information can help the technician understand how the circuit is designed and where testing should take place.
That process naturally takes longer than simply reading a fault code.
WHEN DO YOU USE AN OSCILLOSCOPE?
Some electrical and electronic problems require more detailed testing.
An automotive oscilloscope allows us to examine electrical signals as waveforms.
This can reveal behaviour that isn't necessarily visible from a simple voltage reading or fault-code description.
Depending on the problem, oscilloscope testing can be useful for investigating certain sensors, actuators, communication signals and intermittent electrical faults.
It isn't necessary for every diagnostic job.
It is another tool available when the investigation requires it.
TECHNICAL INFORMATION MATTERS TOO
Testing is only useful if you understand what the results should look like.
Professional technical information can provide details such as:
- Wiring diagrams
- Component locations
- System descriptions
- Test procedures
- Electrical information
- Specifications
- Manufacturer-related technical data
This allows technicians to compare what the vehicle is actually doing with how the system is designed to operate.
It is another reason proper diagnostics involves considerably more than owning a scan tool.
PREVIOUS REPAIRS CAN COMPLICATE DIAGNOSIS
Sometimes a vehicle arrives after several attempts have already been made to repair the problem.
Parts may have been replaced.
Wiring may have been altered.
Fault codes may have been repeatedly cleared.
Components may have been disconnected.
In some cases, the original fault is still present alongside a new problem introduced during previous repair attempts.
That can change the diagnostic process significantly.
If previous work has been carried out, tell the workshop exactly what was done and which parts were replaced.
That information can save valuable diagnostic time.
WHY CAN'T YOU JUST START REPLACING THE MOST LIKELY PART?
Because “most likely” and “confirmed” are not the same thing.
Replacing a part may occasionally solve the problem.
But if it doesn't, the customer has paid for a component that may never have needed replacing and the original fault is still there.
Then another part gets tried.
And perhaps another.
This is often referred to as parts swapping or using the parts cannon.
It can become very expensive.
Spending time diagnosing the fault first can make much more sense than spending money replacing components based on assumptions.
DIAGNOSTIC TIME IS WORKSHOP TIME
There is also an important practical point.
A technician carrying out diagnostics is working on the vehicle.
Reading technical information, analysing data, checking wiring, testing circuits, taking measurements and reproducing faults are all part of the repair process.
The vehicle may not look dramatically different while that work is happening.
There may be no pile of new parts next to it.
But the technician is gathering the information needed to make the right repair decision.
Finding the problem is part of fixing the problem.
HOW CAN YOU HELP YOUR TECHNICIAN DIAGNOSE THE FAULT?
Before bringing the vehicle in, pay attention to exactly what it is doing.
Useful information includes:
- When the problem started
- Whether it is getting worse
- Whether it happens hot or cold
- Whether it happens at a particular speed
- Whether it happens under acceleration
- Whether it happens while braking or turning
- Which warning lights appear
- Whether restarting the vehicle changes anything
- Whether the fault is constant or intermittent
- What repairs have recently been carried out
Videos can also be extremely helpful for intermittent noises, dashboard warnings or behaviour that may not happen again at the workshop.
THE CBC APPROACH TO DIAGNOSTIC TIME
At The Cape Brake Co, we don't believe diagnostics should be rushed simply to produce an answer.
We use professional diagnostic equipment, technical information, live-data analysis, electrical testing and oscilloscope testing where appropriate.
Sometimes the answer becomes clear quickly.
Sometimes the evidence takes longer to uncover.
Our objective remains the same:
Understand the fault before recommending the repair.
Because spending more time finding the right answer can be far better than spending more money replacing the wrong parts.
HAVE A FAULT THAT'S DIFFICULT TO PIN DOWN?
If your vehicle has an intermittent warning light, electrical problem, starting issue, loss of power or another fault that seems to come and go, tell us exactly what you've noticed.
The more information you can give us about when, where and how the problem happens, the better.
Ask the Workshop Assistant or WhatsApp The Cape Brake Co.
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