Code Clearing: Finding the solution in the fine print

By Jordan Coseni

There’s a reason a lot of technicians dread having to diagnose emissions-related failures on light duty diesel trucks and vans. These vehicles can send confusing signals, and codes can be difficult to clear.

Over the past year or so, I’ve noticed a spike in calls from shop owners and technicians asking for help on these dreaded jobs.

Usually, the vehicles arrive with several codes showing, and one or more dash warnings that indicate the vehicle is in limp mode. The driver may or may not be informed that the emissions systems needs service.

Almost all technicians can resolve many of these issues. They’re not actually that difficult. But clearing the dash warnings and engine codes is another matter altogether. Techs often run into trouble in that final step of the repair.

When dealing with
emissions-related failures,
you need to read descriptions
and code information
very carefully.
This is where a lot of
technicians get hung up.

So is there a common denominator in problems like this? Actually, there might be.

Let’s look at a recent case I got called in on. It involved a 2016 Ford F-450 with the 6.7L Powerstroke. This truck first came in with a host of reductant-related codes. The technician was able to get many of the codes to clear after replacing a NOx sensor. However, it appeared that several faults still existed.

Messages showing on the dash were “Service DEF System” and “Limited to 80km-h.” Also, a P207F code was stored in the PCM.

The technician attempted to resolve the remaining issues by replacing the DEF fluid and running several forced SCR resets with the scan tool. Neither of these cleared the faults… and this is the point at which I was called in to help diagnose the issue.

I’ve always been taught that you need to understand what you’re dealing with before you can accurately diagnose a vehicle.

When dealing with emissions-related failures, you need to read descriptions and code information very carefully. In many cases, the vehicle is already fixed, even though a fault code or message remains. If you don’t read it carefully, though, you may think issues are still present.

This is the common denominator where many technicians get hung up. It was certainly the case with this F-450.

Once I started digging into the code information, I discovered that this fault cannot be cleared until a very specific drive cycle is completed. The same applies for the “Service DEF System” message on the dash. In order for our P207F to clear, the vehicle manufacturer has developed a multi-step protocol that must be followed to the letter, and several specific data PIDs that must be monitored.

Specifically, you have to keep a close eye on:

* reductant levels;

* EGT sensors;

* RPM; and

* vehicle speed.

First, the reductant level in the scan data needs to read 100%. If it reads anything less than that, simply add more DEF fluid to the tank to bring the level up.

Once the reductant level is confirmed, the truck needs to be started and held at 1000 RPM while you monitor the EGT data.

All three EGT sensors must read 130C for a minimum of two minutes.

Once the correct temperatures are met, the truck needs to be accelerated steadily up to 80 km-h, followed immediately by a closed throttle deceleration for six seconds. That accel/decel procedure must be performed three times.

Next, all three EGT sensors must read 220C.

Once the proper temperature is reached, the truck then needs to see three moderate to heavy acceleration events for a minimum of three seconds.

If the fault does not clear the first time, repeat the procedure, paying very close attention to each step. It can often take several attempts.

That particular drive cycle was very specific to the fault code we retrieved. But there are many other emissions-related codes that require their own very precise reset procedures. Many of these protocols can differ wildly, depending on what vehicle make or emissions system you’re working on.

The bottom line is to take your time to read the codes and messages very carefully, making sure you fully understand what you’re dealing with. Taking a short cut here could lead to confusion, and cost you a lot of precious diagnostic time chasing a fault which may not even exist.

With stricter emissions regulations being implemented each year, it is evident that these complex emissions treatment systems are here to stay for the foreseeable future. You might as well get used to dealing with them efficiently and effectively.

Jordan Coseni is a technician and professional troubleshooter with Auto Aide Technical Services in Barrie, Ont. You can reach him at jordanc@autoaide.ca