Replacement DEF sensors are now available.
By Steve Bertling, F460062, & Ken Carpenter, F312233
June 2024
Feedback from diesel engine manufacturers indicates that a recall notice related to the DEF sensor (also called the DEF head) problem is in the works, so RVers who have experienced this will be able to get it fixed at no charge under the recall program. At press time, the recall was expected to be announced soon. Reportedly, an adequate supply of replacement parts now exists. However, no change has been made in the EPA rules associated with derating an engine once the DEF head quality sensor reports a problem. The sensor tests DEF quality (concentration of DEF in the tank), temperature (must be within acceptable temperature range of optimal performance), and level (must be an adequate volume in the tank). In the event any of these tests fail, the driver is usually notified through a warning message on the driver information center (DIC). The warning message could be one of the following:
- Exhaust Fluid Quality Poor: This message is displayed when the selective catalytic reduction (SCR) efficiency is below a calibrated value.
- Diesel Exhaust Fluid Warning Lamp On: This message is displayed when the DEF system requires immediate service.
- Other Exhaust Fluid Quality Related Concerns: This message is displayed when there are other DEF quality-related concerns.
The DEF warning light, if accompanied by the check engine light (red), will trigger a derating process that ultimately results in limiting vehicle speed to 5 mph. This takes place over a several-hour period to allow time to get to a service facility. A driver will be left on the side of the road only if he or she ignores these two warning lights. Prompt response to this warning is critical.
Besides the time factor, any of the following will trigger the 5-mph limit:
- Idling for more than an hour.
- Turning off the engine.
- Refueling.
Typically, if a DEF sensor fails, it is easy to simply install another one. However, the global shortage of these sensors created a problem for vehicle owners who could not get a replacement. This left many RV owners fearful of being disabled along a busy highway and reluctant to use their motorhomes.
After the shortage of DEF sensors impacted vehicle owners, both individual RV owners and engine manufacturers developed solutions that enabled operation until the sensor supply problem was solved. The EPA has approved all the software solutions provided by the engine manufacturers, and manufacturers have already begun implementing many of them. Each manufacturer has numerous engine families, and each family typically requires a unique software solution. Manufacturers determined the pace and sequence for software deployment for each of their engine families. Vehicle owners were advised to contact their local dealership’s service department for information about when a solution for their specific vehicle would be available.
Under the recall program, notices are to be sent by manufacturers directly to the vehicle owner along with applicable instructions. Anyone who had the temporary fix must respond to the recall.
With the resolution of the supply problem, the software flash is no longer available, and the DEF head is to be replaced. Rather than wait for the notice, affected owners should be able to get the repair by contacting their dealer or service center.
It’s important to note that the recall notice will be sent to the registered owner. Owners need to make sure they are listed as the owner of record with the motorhome manufacturer, the engine manufacturer, and the chassis manufacturer.