Modern diesel trucks have a lot of warning lights, and the exact symbols vary by manufacturer. This guide covers the most common ones in general terms. Always check your owner's manual for your truck's specific meanings.
A basic rule: amber means get it checked soon; red means stop safely and find out why before driving further.
Check engine light (amber)
The engine control system has detected a fault. It could be minor or the early sign of something bigger. Get it diagnosed soon — emissions-related faults can also cause trouble at your next Clean Truck Check.
Stop engine light (red)
A serious fault. Many trucks will derate or shut down to protect the engine. Pull over safely as soon as you can and call for help.
DPF / regeneration lights
These relate to the diesel particulate filter. A lamp may tell you the filter needs a regeneration or that regeneration is in progress. If the light keeps coming back or the truck derates, have the system checked — repeated regen issues often have an underlying cause.
High exhaust system temperature
Usually shown during regeneration, when exhaust temperatures are higher than normal. Be careful where you park — keep the exhaust away from dry grass or anything flammable.
DEF level and DEF system warnings
Low diesel exhaust fluid, poor DEF quality or a problem in the SCR system. Ignoring DEF warnings can lead to power derates. Refill with quality DEF, and if the warning continues, book diagnostics.
Oil pressure and coolant temperature
Low oil pressure or high coolant temperature can quickly damage an engine. Stop safely and investigate. Don't keep driving to “make it home.”
Battery / charging system
Indicates a charging problem — alternator, belt, wiring or batteries. Trucks can run for a while on battery power and then stop unexpectedly, so get it checked soon.
What to do when a light comes on
- Note whether it's amber or red, steady or flashing.
- Take a photo of the dash — it helps the technician.
- If it's red, or the truck derates, overheats or loses oil pressure, stop safely.
- Book diagnostics and upload the photo with your booking.
Frequently asked questions
Can I clear the warning light myself?
Clearing a code doesn't fix the problem, and the light will usually return. It also removes information a technician could use. It's better to get it diagnosed.
Can I upload a photo of my dash when I book?
Yes. The booking form accepts photos of warning lights and problem areas.