Guide
Car Problem Comes and Goes? How to Record an Intermittent Fault
The car won't start this morning, but is fine by lunchtime. A warning light comes on, then disappears. A noise only happens sometimes. Intermittent faults are frustrating — especially when "the car behaved perfectly when the mechanic looked at it." This guide helps you gather the observations that actually help, without trying to diagnose it yourself.
Your job is not to name the fault. Your job is to describe what happened.
1Why intermittent faults are frustrating
Some problems only occur under specific conditions — a certain temperature, a particular speed, after the car has sat, or only when it is damp. By the time someone looks at it, the conditions have changed and the fault has gone. That does not mean it is not real. It means the clues matter more than usual.
2Do not worry about naming the fault
You do not need to know what is wrong. In fact, guessing can send help in the wrong direction. What helps is a clear, honest description of what you saw, heard and felt — and when. Leave the diagnosing to someone with the right equipment.
3Record when it happens
Timing is one of the most useful things you can note. Does it happen:
- First start of the day
- When the engine is hot
- When the engine is cold
- After rain or damp weather
- After a long drive
- After the car has been sitting
- While accelerating
- While braking
- At certain speeds
- While turning
- While idling
These are observations, not diagnoses — a condition does not automatically point to a particular fault. But it gives a mechanic a much better place to start.
4Record what happens
Describe what you actually experienced:
- A click
- No crank at all
- Rough running
- Hesitation
- Loss of power
- A warning light
- Vibration
- A smell
- A new noise
- An electrical system stops working
5Photograph warning lights — when safely parked
A photo of the exact symbol or dashboard message is genuinely useful. But only capture it when you are safely stopped.
Never use your phone while driving to photograph a warning light. Note the colour and whether it was steady or flashing, then photograph it once parked.
6Record the exact warning message
If the dashboard displays text — for example "Engine fault, reduced power" or "Check hybrid system" — write it down or photograph it when parked. The exact wording can be more useful than the symbol alone, because many cars share similar icons for different messages.
7Record how long the problem lasts
Duration is a useful clue. Does it last:
- A few seconds
- Several minutes
- Until the car is restarted
- Only once, then not again
- Every few days
8Does restarting change anything?
Note whether turning the car off and on again clears the fault, or changes it. This is worth recording — but do not repeatedly restart a vehicle that feels unsafe. If the car has cut out or feels wrong to control, stop and get help rather than experimenting.
9Weather and temperature
Note whether the fault happens in the wet, in the cold, after the car has been in the sun, or only when the engine is fully warmed up. These can be useful observations. They do not diagnose the fault on their own — but a pattern across weather or temperature can help.
10Create a simple fault diary
A short written record over a few days is often the single most useful thing you can bring. Use this template — on paper or in your phone's notes:
Fault diary entry
- Date:
- Time:
- Location:
- Engine hot / cold:
- Weather:
- What happened:
- Warning light / message:
- Sound:
- Smell:
- How long it lasted:
- What happened next:
Keep this for yourself — we do not collect or store your fault diary through this site. Bring it with you, or read it out, when you get in touch.
11Why diagnostic scanners don't always tell the whole story
- Some faults create stored codes that remain even after the symptom has gone
- Some faults leave no code at all
- A code points to a system or component, but does not always confirm the exact part at fault
- Codes are clues rather than automatic diagnoses
A clear fault diary and a diagnostic scan together are usually more useful than either on its own.
12When intermittent becomes urgent
Some intermittent faults should not wait for the next episode. Treat it as urgent if you notice:
- A change in braking
- A change in steering
- Severe loss of power
- The engine cuts out
- Smoke
- Overheating
- A strong burning smell
- The vehicle becomes difficult to control
13What to tell the mechanic
When you get in touch, share your fault diary and the key details — when it happens, what happens, how long it lasts, and whether anything seems to trigger it. The more specific the observations, the better.
14Why a mobile diagnostic visit can sometimes help
If the vehicle is safely parked, a mobile diagnostic visit can read stored codes and test relevant systems where the car sits — which is often easier than trying to recreate the fault on a workshop forecourt.
A mobile visit is a sensible starting point, but it does not guarantee the fault will be found — especially if it is not present at the time. It narrows things down.
Frequently asked questions
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