Diagnostic Technique - Symptoms versus Problems

Not using the correct diagnostic techniques can make it difficult to find the actual cause of a problem. This is important because most problems will have more than one possible cause. The use of the process shown below is a good first step in learning to diagnose successfully. When the list of possible causes has been established the next step involves finding which one is at fault. One effective technique to determine a cause is to find the symptoms associated with each possible cause and create a list. Most conditions have related symptoms. These symptoms are an effective tool when used properly.

Diagnostic Technique Example:

To better understand this system of diagnosis, notice the example below. Here we will use a RWD vehicle experiencing fast pad wear on only one side. Both inner and outer brake pads on on side are wearing much faster than the pad on the opposite side as shown:



Using a diagnostic approach we would come up with the following list of possible causes:

- Sticking caliper piston on side with pad wear problem

- Check valve brake hose on side with pad wear problem

- ABS modulator not allowing fluid release on side with pad wear problem

- Restricted brake hose on side opposite the side with pad wear problem

- Hydraulic restriction higher than brake hose on side opposite side with wear problem.

If we take the same list and add the symptoms each condition would generate we have the following:

1. Sticking caliper piston

2. Check brake hose

3. ABS modulator

4. Restricted brake hose

5. Hydraulic restriction higher than brake

1. Wheel drag

2. Wheel drag

3. Wheel drag

4. Pull to side with pad wear

5. Pull to side with pad wear

Armed with the list above, the first step in any diagnosis would be a test drive. A test drive would allow for a check for a pull and make sure the brakes are at operating temperature. This could be important in duplicating the drag associated with items number 2 & 3. Using the technique of looking for supporting symptoms is one of the most effective diagnostic techniques available.

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