Bottom Line
Maintenance Q&A
Too cool to heat up

By Paul Abelson
senior technical editor


Q. I changed carriers so I could be home more often. The company put me on routes with a lot of city driving. I got a 2008 Freightliner with a Detroit and an UltraShift transmission. The fleet I got it from uprated it to 500 hp.

Several warning lights keep coming on, then start flashing. The fleet couldn't find the owner's manual, so I have no idea what the pictures are. After a few times, a red light came on that read "stop engine."

I did and called a Freightliner dealer. He started the engine and came out of the cab. He waited around for about 45 minutes, went back into the cab, and hit me with a bill for a one-hour road service call. It happened again a few weeks later.

I never had these problems before. I can't afford road service every six weeks or so. Did they screw something up when they uprated the engine?

A: Your engine has a diesel particulate filter as part of the emissions control equipment. It captures soot in its porous ceramic body.

Eventually, the soot builds up and clogs the filter. It can be removed by a process called regeneration.

The temperature inside the ceramic is raised to almost 1,200 degrees. That burns the soot, converting almost all of it to carbon dioxide gas. The process is monitored and controlled by computer.

When driving over-the-road, the engine is hot and regeneration takes place automatically. In city driving, particularly pickup and delivery work, the engine rarely gets warm enough to initiate the regen. It must be initiated manually.

As you drive, the engine controller monitors the engine and emissions control systems. When soot level is too high, the DPF regeneration lamp will stay on. If you drive on the highway under load, a regen will start automatically.

If the light starts flashing, you should park and start a parked, or manual, regeneration. There's also a high exhaust temperature system lamp that warns when the exhaust is extremely hot. It may come on after a regen is started.

If you must stop, be sure you won't hurt people or equipment nearby. The red "stop engine" lamp warns of a fault that could damage the engine. The controller will derate and may stop the engine. That's what you experienced.

Here's how to avoid future road service calls.

If the DPF lamp begins flashing, park and regenerate the DPF as soon as possible. Otherwise, the "check engine" light will come on and the engine will lose 25 percent of its power. It may shut down.

If regeneration is still not done, the red "stop engine" light will come on. Move the vehicle away from people, flammable materials and overhead structures, including trees and power lines.

Do these in order:

  1. Set the parking brake.
  2. Turn off and restart the engine. On restart, the engine must reach 600 rpm.
  3. Place the transmission in neutral. Shift to drive and back to neutral.
  4. Release the parking brake. Wait five seconds and reapply the brake.
  5. Press and hold the "Parked Regen" switch for five seconds. This initiates the regeneration. The engine speed will ramp up and the switch indicator lamp will stay on when the cycle starts.

If the indicator still blinks, make sure all conditions are met. Once started, the cycle will take between 20 and 60 minutes. If you don't do all the steps within 30 seconds of key on, the engine will shut down. If you need to cancel a parked regeneration, hold the DPF switch to the "on" position for five seconds and release.

When the regeneration is complete, the engine rpm will return to normal idle and warning lights will be off. The truck can now be driven. If the DPF lamp comes back on, the regeneration failed. Contact your dealer.

If the key is turned off, the service brake is applied, the transmission is taken out of neutral, or your Detroit Diesel is not at 185 degrees, then the regeneration will stop and must be restarted.

It would also be advisable to contact a Freightliner dealership and get a manual that shows the common alerts and warning lights for your truck for when you have problems in the future.LL

Senior Technical Editor Paul Abelson is a Life Member of OOIDA, holds an Illinois CDL, is active in the Technology & Maintenance Council and is a recipient of the Lifetime Achievement Award from the Truck Writers of North America. He can be reached at