Skip to content A truck develops a warning light halfway through a run. It loses performance for several minutes, makes an unusual noise or starts vibrating. By the time it reaches the workshop, everything appears normal again.
Intermittent faults can be frustrating for drivers, fleet managers and mechanics. A mechanic can inspect the truck, scan its systems and test components, but a fault that only appears under certain driving conditions may not show itself during the workshop visit.
Good notes can give the mechanic a much better starting point.
For an effective intermittent truck fault diagnosis, record what the truck was doing before, during and immediately after the problem. Details such as route, load, speed, warning lights, temperature and how long the symptom lasted can help connect the fault with the conditions that trigger it.
This guide explains what drivers should record and how fleet managers can pass that information to the workshop.
Some faults are present all the time. A broken component, constant leak or failed light can often be confirmed quickly.
A recurring truck fault can be different.
The symptom may depend on:
The truck may arrive at the workshop cold, unloaded or operating at a different speed from when the fault occurred.
That changes the conditions.
The mechanic now has two jobs: identify the problem and work out what causes it to appear.
Driver notes can narrow that search.
The NHVR’s 2026 Master Code recommends defect-reporting processes that let drivers record observations such as changes in vehicle condition, leaks, stains and cracks. It recommends providing a way for drivers to send photos of problem areas. The guidance states that post-shift checks can be useful since the driver may know where to look based on the truck’s behaviour during the shift.
You do not need to provide a mechanical theory. You need to provide accurate observations.
A useful fault report starts with basic facts.
For fleet driver defect reporting, each report should clearly identify which truck had the problem and when it happened.
| What to record | Example | Why it helps |
|---|---|---|
|
Truck ID |
Rego ABC12D / Fleet 27 |
Links the report to the correct vehicle |
|
Date and time |
5 October, 2:40 pm |
Helps compare repeat events |
|
Odometer |
286,450 km |
Provides maintenance context |
|
Route |
Brookvale to Parramatta |
Shows road and traffic conditions |
|
Load |
Near full load |
May reveal load-related symptoms |
|
Road type |
Motorway, steep grade |
Helps identify triggering conditions |
|
Weather |
Hot, dry |
Adds operating context |
|
Speed |
About 80 km/h |
Helps reproduce the event |
|
Engine condition |
Warm after two hours |
Shows whether temperature may matter |
|
Fault duration |
About 20 seconds |
Shows whether the event was brief or sustained |
You do not need perfect measurements.
A simple note such as “warning came on after 40 minutes of motorway driving with a loaded truck” can be much more useful than “warning came on sometime today”.
Think back 30 seconds to a few minutes.
Was the truck:
These details help answer one of the first diagnostic questions: what changed when the symptom appeared?
If the same issue has occurred more than once, send the previous reports with your booking. A pattern across several events may give the mechanic a stronger lead than one event viewed on its own.
When deciding what to tell a truck mechanic, describe the symptom rather than guessing at the failed part.
“The engine made a metallic tapping sound under acceleration” is useful.
“I think the injectors are failing” is a diagnosis, not an observation.
Your mechanic needs the first statement more than the second.
Record:
A photo can help capture the exact warning message. Pull over safely before using a phone or camera.
Try to describe:
Record where the noise seemed to come from and what the truck was doing when you heard it.
Unusual smells can provide useful clues.
Examples include:
Do not investigate a strong fuel, smoke or burning smell in an unsafe location. Stop where safe and follow your company’s incident or defect procedure.
Record where you felt the vibration:
Note whether it changed with road speed, engine speed, braking or acceleration.
Australian heavy-vehicle inspection data shows why detailed observations matter. The NHVR inspected 9,082 vehicles and combinations during its 2024 National Roadworthiness Survey. Seventy-five per cent of units passed inspection.
For rigid trucks, 39% of units recorded at least one non-conformity. Lights and reflectors had a 14% non-conformity rate, brakes 14%, and engine, driveline and exhaust items 12%.
These figures do not measure intermittent faults. They do show that several systems drivers can observe during normal operation are common areas where defects are found.
A photo can preserve evidence that may be gone by the time the truck reaches the workshop.
Useful photos may include:
Do not place yourself under a truck on the roadside. Do not open hot cooling systems. Do not touch damaged electrical components. Do not film or photograph anything when driving.
Yes, when the truck displays a code or a fleet-approved diagnostic system has already captured one.
Record the code exactly.
Do not rely on an online description of the code as the diagnosis. One code can be linked to several possible causes, and the mechanic still needs to test the system.
Avoid clearing stored codes unless a qualified mechanic or your fleet procedure asks you to. Stored diagnostic information may give the workshop another clue about what happened.
If your truck has shown the same symptom several times, send the completed notes to Auramotive when requesting a diagnostic booking. That gives the workshop useful information before the truck arrives.
A driver fault report does not decide that a truck is safe.
If you suspect a safety problem, stop in a safe place and follow your fleet’s defect procedure. Report the issue to the relevant manager, operator or maintenance contact.
Signs requiring immediate attention can include:
The NHVR states that a heavy vehicle is unsafe when its condition, components or equipment make its use unsafe or endanger public safety. Where a defect presents an imminent and serious safety risk, the vehicle may need immediate repair and cannot continue operating on the road unless movement is permitted under the applicable conditions.
If you are uncertain, do not try to prove the fault by continuing to drive. Contact your fleet manager or mechanical workshop for direction.
Use this truck fault report template whenever a problem appears and later disappears.
Registration:
Fleet number:
Make/model:
Odometer:
Driver:
Date:
Time:
Location/route:
Approximate load:
Weather:
Road conditions:
Approximate speed:
Time operating before fault:
Warning light/message:
Noise:
Smell:
Vibration:
Change in performance:
How long did it last?
What was the truck doing when it started?
Did the problem stop by itself?
Did it return after restarting?
Photos attached: Yes / No
Video recorded after safely stopping: Yes / No
Fault code recorded: Yes / No
Code/message:
Has this happened before? Yes / No
Previous date or report number:
Were the conditions similar?
Vehicle stopped: Yes / No
Fleet manager contacted: Yes / No
Workshop contacted: Yes / No
This format gives the workshop a timeline rather than a vague symptom description.
A fleet manager can build the driver’s report into a simple maintenance record.
Use a defect number, job number or digital record so photos, mechanic notes and repair invoices stay linked.
Three reports saying “warning light appeared” may seem vague.
Three reports showing that the same warning appears after 60–90 minutes under load gives the workshop a clearer pattern.
After inspection, record:
If the fault does not return after repair, close the report under your fleet process.
If it returns, reopen the history rather than starting from zero. Send the previous repair notes back to the workshop.
Where your business uses formal defect management, record who reviewed the repair and when the vehicle returned to service.
Intermittent faults are easier to investigate when the workshop receives a clear record of the conditions surrounding each event.
For intermittent truck fault diagnosis, capture the truck ID, route, load, warning messages, sounds, smells, driving conditions and duration. Add safe photos when useful. Keep previous reports when the problem repeats.
Your role as the driver or fleet manager is not to diagnose the component. Your role is to preserve the clues.
Auramotive Mechanical Solutions provides truck fault diagnosis and repairs from its Brookvale workshop, with experience across mechanical, electrical and heavy diesel systems.
Send your completed fault notes when booking your truck with Auramotive. The extra detail can help the mechanic start with a clearer picture of when the issue occurs and what needs to be checked.
No, unless a mechanic or your fleet procedure directs you to clear it. Record the code or dashboard message and leave stored diagnostic information available for the workshop where practical.
Give the mechanic your fault report, photos, codes and previous repair history. The workshop can use these clues to decide which systems need inspection or testing.
Yes. A disappearing warning or symptom can still point to a developing problem. Record what happened, how long it lasted and whether restarting changed it.
Only when the truck is safely stopped. Never use a phone to photograph or film a fault when driving.
Keep each report linked to the vehicle’s repair history. Compare load, route, operating time and other conditions across each event, then provide the full history to the workshop at the next diagnostic booking.