By TRT Road Service
On a Detroit DD15 or DD13, read the lamp first, because the lamp tells you how urgent the problem is. A solid DPF lamp means a parked regeneration may be needed, and a flashing one means do it as soon as you can. A flashing DPF lamp with a check engine lamp means the engine is derated, and a red stop engine lamp means shutdown. If a second parked regeneration fails, call for service. That order comes from Detroit’s own driver card, a copy hosted by a Freightliner dealer.
Read the lamp before you read the code
A fault code names a part or a system. A lamp tells you what the truck needs from you right now. On the road, the lamp is what you can act on. The code is what a technician reads with a diagnostic tool afterward.
Detroit’s driver card lists each aftertreatment lamp with its meaning and the driver action. It is a Detroit Diesel Corporation sheet from 2013, so a newer truck’s dash or message center may word things differently. The lamp logic below still tells you how to rank the problem.
What each aftertreatment lamp is asking for
Start with the lamps that cost you the least time, and work up.
Lamps you can drive with
- HEST lamp, solid. Per Detroit’s card, the exhaust is at high temperature and the truck is slow or parked. No change in driving style is required. When parked, keep the truck clear of people and flammable materials or vapors.
- Check engine lamp (amber). Engine controls or aftertreatment parts have an issue. The card says the truck can be driven to the end of the shift. Call for service.
- Malfunction indicator lamp (MIL). There may be a problem with the emission controls. The card says to call for service if the MIL is still on after three drive cycles. It also warns that a long drive with the MIL on can damage the engine or aftertreatment.
Lamps that want action now
- DPF lamp, solid. A parked regeneration may be needed. The card says to do one, or bring the truck to highway speed so the filter can clean itself.
- DPF lamp, flashing. A parked regeneration is needed as soon as possible. The filter is close to its limits.
- Flashing DPF lamp with the check engine lamp. The engine is derated. The filter has reached its limits. A parked regeneration must be done.
- Flashing DPF lamp, check engine lamp and red stop engine lamp. The card calls this engine shutdown. The filter has gone past its limits.
No change in driving style is required. Source
Engine derated, a parked regeneration must be done. Source
How a parked regeneration works, and what stops it
A parked regeneration cleans the DPF while the truck sits still. Detroit’s card says it may take up to 40 minutes. It is done when the engine returns to idle and the DPF lamp stays off. The HEST lamp may stay on, and the truck can still be driven.
The card also lists what ends the process early. Turning the key off, pressing the clutch, putting the truck in gear or releasing the parking brake all stop it. So leave the truck alone while it runs.
The exact start steps depend on the engine year. The card says some of its steps are not needed on GHG14 engines or later. Follow the prompt on your own dash.
Park outdoors and away from anything that burns. Stay with the truck.
When it is not safe to keep driving
Do not push on when the lamps say derate or shutdown. The card’s rule is plain. A parked regeneration must be done. If it exits and the lamps stay on, repeat it. If the second try fails, call for service.
With the red stop engine lamp, the card adds a warning. The engine can be restarted, but a parked regeneration must start within 30 seconds or the engine shuts down again.
Two other lamps can also lead to a derate. A restricted fuel filter lamp gives you one to three days to get service, says the card. A water in fuel lamp means the water separator must be drained, or the engine will derate.
Restart, then start a parked regeneration within 30 seconds or the engine shuts down. Source
DEF lamps and the speed limit you may see
The DEF gauge has its own lamp. A very low level shows a solid lamp. According to Detroit’s card, an empty tank shows a flashing lamp and a 55 mph limit. Empty and ignored adds the stop engine lamp and a 5 mph limit until DEF is detected in the tank.
The card also warns that the wrong fluid in the DEF tank cuts engine performance. Put only DEF in that tank.
Those speeds are from the 2013 card, and newer software changes them. Daimler Truck North America says it is updating about 330,000 in-service vehicles with revised DEF software. The release covers DD15 engines from model years 2021 to 2025 and DD13 engines from model years 2022 to 2025. In final inducement, the speed limit rises from 5 mph to 25 mph.
The DEF tank level logic stays the same, and vehicles must still be repaired. For a longer look at this derate, see our article on what a DEF and DPF derate means on I-40.
Rises from 5 mph to 25 mph on updated DD15 (model years 2021-2025) and DD13 (2022-2025). Source
Why the code still matters after the lamp
A lamp does not say which sensor, line or part is behind it. The card’s own rule is to call for service when the second parked regeneration fails. That is the point where the code is worth reading, so you stop guessing.
TRT Road Service reads Detroit codes at your breakdown location with JPRO Professional dealer-level fault code reading. Our heavy-duty diagnostics service covers Detroit engines, and our crew comes to you. There is no shop drop-off. Tennessee personally handles most jobs.
We come to your breakdown location. Open 24/7.
Frequently Asked Questions
Quick answers to the questions people ask before they call or book.
Is a solid HEST lamp a fault?
Not by itself. Detroit’s card says a solid HEST lamp means the exhaust is at high temperature while the truck is slow or parked. No change in driving style is required. Keep the truck away from people and flammable materials when parked.
Can I run a parked regeneration if the stop engine lamp is on?
The card says yes, but with a short window. The engine can be restarted, and a parked regeneration must begin within 30 seconds or the engine shuts down. If the second attempt fails, call for service.
Which Detroit engines got the new DEF software?
Daimler Truck North America names DD15 engines from model years 2021 to 2025 and DD13 engines from model years 2022 to 2025. Your dealer or a technician can confirm whether your truck has the update.
Does TRT come to the truck?
Yes. TRT is mobile only, so the mechanics come to your breakdown location. We serve I-40 from Seligman through Kingman and Needles to Barstow, and AZ-95 from Searchlight to Parker.
Derated or shut down on a Detroit? Call now
If a parked regeneration did not clear the lamps, stop retrying.
Call TRT Road Service
Call TRT Road Service at (928) 577-1496. We are open 24/7. You can also use the contact page to describe what the dash shows. Tell us the lamps you see and the engine year, and we will take it from there.
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