The Patient Writes the Prescription


I took the photo above in my brother-in-laws 2015 Jeep Grand Cherokee EcoDiesel. It says “Exhaust Filter Nearing Full Safely Drive at Highway Speeds to Remedy.”

I’d never seen anything like that before neither had he – it seemed like a terrible idea at first. What if the person couldn’t drive at highway speeds right then? Spending an unknown time driving at highway speeds wasting gas also seemed unpleasant. My brother-in-law said that he was having issues with the car before, but it wasn’t until the Jeep downloaded a software update that it displayed this message on the dashboard.

My own car will be 14 years old this year (nearing an age where it can get its own learner’s permit?), so I had to adjust to the idea of a car that updated itself. I was intrigued by the issue and looked around to see what other Jeep owners had to say.

I found another unhappy customer at the diesel Jeep forum:

At the dealer a very knowledgeable certified technician explained to me that the problem is that we had been making lots of short trips in town, idling at red lights, with the result that the oil viscosity was now out of spec and that the particulate exhaust filter was nearly full and needed an hour of 75 mph driving to get the temperature high enough to burn off the accumulated particulates. No person and no manual had ever ever mentioned that there is a big problem associated with city driving.

And further down the rabbit hole, I found it wasn’t just the diesel Jeep. This is from a Dodge Ram forum:

I have 10,000K on 2014 Dodge Ram Ecodiesel. Warning came on that exhaust filter 90% full. Safely drive at highway speeds to remedy. Took truck on highway & warning changed to exhaust system regeneration in process. Exhaust filter 90% full.
All warnings went away after 20 miles. What is this all about?

It looks like Jeep added a supplement to their owners manual in 2015 to explain the problem:

Exhaust Filter XX% Full Safely Drive at Highway Speeds to Remedy — This message will be displayed on the Driver Information Display (DID) if the exhaust particulate filter reaches 80% of its maximum storage capacity. Under conditions of exclusive short duration and low speed driving cycles, your diesel engine and exhaust after-treatment system may never reach the conditions required to cleanse the filter to remove the trapped PM. If this occurs, the “Exhaust Filter XX% Full Safely Drive at Highway Speeds to Remedy” message will be displayed in the DID. If this message is displayed, you will hear one chime to assist in alerting you of this condition. By simply driving your vehicle at highway speeds for up to 20 minutes, you can remedy the condition in the particulate filter system and allow your diesel engine and exhaust after-treatment system to cleanse the filter to remove the trapped PM and restore the system to normal operating condition.

But now that I’ve had time to think about it, I agree with the remedy. After all,my own car just has a ‘check engine’ light no matter what the issue. Twenty minutes on the highway is a lot easier than scheduling a trip to a mechanic.

What could be done better is the communication of the warning. It tells you what to do, and sort of why, but not how long you have to execute the action or the consequences of not acting. The manual contains a better explanation of why (although the 20 minutes there does not match the 60 minute estimate of at least one expert), not that many people read the manual. Also, the manual doesn’t match the message. The manual says you’ll receive a % full, but the message just said “nearly.” The dash display should direct the driver to more information in the manual. Or, with such a modern display, perhaps scroll to reveal more information (showing partial text, so the driver knows to scroll). Knowing the time to act is more critical, and maybe a % would do that since the driver can probably assume he or she can drive closer to 100% before taking action. It looks as though the driver needs to find a way to drive at highway speeds right now, but hopefully that is not the case. I can’t say for sure though, since neither the manual nor the display told me the answer.