Introduction to Automatic “Auto Desorb“ Feature on MX Powered Peterbilt Chassis

By Allstate Peterbilt Group | Posted in Diesel Technicians & Mechanics on Monday, July 15th, 2019 at 7:29 pm

On May 7, 2018, Engine software version RC 7 was released to add a new functionality to the MX engine family.

Automatic regens or “Auto Desorb,” as it is referred to by Paccar, is your truck’s ability to do small maintenance regenerations without the driver’s interaction. Think of them as automatic mini regens to help prevent the operator from having to perform a mandatory stationary regen. As we all know, these types of regenerations are required to be initiated by the driver and render the vehicle out-of-service, sometimes for up to an hour. Particularly, if your vehicle idles for more than three hours continuously, operates in cold climates, or is a 2017 year model. It is important to make sure to utilize this new feature to prevent shortened aftertreatment life, nuisance manual regens, and costly downtime.

The following information was released from Paccar as part of field service bulletin E-211:

MX Behavior During Extended Idling

Before MY17 RC7 & MY18 RC2 MX Automatic DPF Warm-up Functionality

  • Manual parked regeneration is requested after a certain amount of idle time (6-18 hours)
  • Manual parked regeneration needs to be initiated by the driver using the regen switch

After MY17 RC7 & MY 18 RC2 MX Automatic DPF Warm-up Functionality

The following characteristics are standard for MY2018 chassis and optional for MY2017 chassis:

  • As a convenience, Automatic DPF (Diesel Particulate Filter) Warm-up may occur automatically without driver input while the vehicle is idling. During extended idling, the vehicle will periodically increase engine speed to perform this function, sometimes without notification to the driver.

*If used, driver will likely not have to perform a parked regeneration after extended Automatic DPF Warm-up Information for Drivers

  • Drivers cannot drive if a Parked Regeneration is requested. “DO NOT DRIVE” displays on the dash. The vehicle is safe to drive if an Automatic DPF Warm-up is occurring.
    • Automatic DPF Warm-up can be stopped by pressing the brake pedal, and then the vehicle can be driven.
The Vehicle is NOT safe to drive during Parked Regeneration.

A “DO NOT DRIVE Parked Regen Required” message displays.

A 10-minute restart delay timer begins if Automatic DPF Warm-up is stopped.

  • If Automatic DPF Warm-up is stopped by the driver, the function will be attempted every 10 minutes until it can be completed.
  • DPF Warm-up functionality can be disabled via SPP or temporarily disabled using the regen inhibit switch.
    • If DPF Warm-up functionality is disabled, a Parked Regeneration may be required after extended idling.
    • If drivers use the inhibit switch to disable Automatic DPF Warm-up, drivers will need to remember to un-inhibit regens before driving
  • Tailpipe exhaust temperatures will remain below 450F (230C)

The chart below explains a list of operator actions that will ACTIVATE or DEACTIVATE the auto desorb feature:

(The following information is taken from the programming guide)

Activate Deactivate
Accelerator pedal not pressed Accelerator pedal pressed
Foot brake not pressed Foot brake pressed
Clutch pedal not pressed if equipped Clutch pressed if equipped
Vehicle in neutral Vehicle not in neutral
Parking brake set Parking brake not set
DPF regen switch is not set to ‘inhibit’ DPF regen switch set to ‘inhibit’
Vehicle speed = 0 Vehicle speed > 0
No related engine or aftertreatment faults Related engine or aftertreatment faults ie: BPV, VGT, EAS overtemps, pre-DOC temp, etc
Coolant at operating temp Coolant not at operating temp
Engine load less than 600 lb-ft* Engine load greater than 600 lb-ft*
If PTO active, engine speed greater than 900 RPM** If PTO active, engine speed less than 900 RPM**
* Engine load threshold varies based on engine speed

** Engine speed threshold varies based on ambient conditions

Automatic DPF Warm-up                      

  • Automatic DPF Warm-up will occur every 3 – 8 hours during extended idling and take 20 to 60 minutes to complete.
    • Engine speed is elevated while Automatic DPF Warm-up is occurring
    • If driver notifications are available, a two-minute countdown timer will alert drivers that an Automatic DPF Warm-up is about to start
  • OBD monitors introduced for Auto DPF Warm-up functionality
    • Regeneration related faults indicate an issue with engine temperature control.
  • Automatic DPF Warm-up will function with PTO or FIC active
    • Auto DPF Warm-up will NOT change engine speed if PTO is active.
    • PTO Engine Speed needs to be above about 900 rpm for Auto DPF Warm-up to occur with PTO active.

Automatic DPF Warm-up Availability

  • MY17
    • Software can be updated to MY17 RC7 to enable Automatic DPF Warm-up Functionality.
    • Functionality will be disabled by default (labels included in SPP to allow customers to enable via PVP).
  • MY18
    • Software can be updated to MY18 RC2 to enable Automatic DPF Warm-up Functionality.
    • MY18 Automatic DPF Warm-up functionality disabled by default on chassis built before 05/01/2018 when updated to RC2.
    • MY18 Automatic DPF Warm-up functionality enabled by default on trucks built after 05/01/2018.

Important Things to Know About DPF Filters 

How do I know if my DPF is regenerating? 

During a regeneration, the engine RPM will raise to create higher exhaust temperatures to assist with the regens. Another indicator to look for is a “high exhaust temperature” warning when the park brakes are set and the vehicle is performing a regen. 

How can I tell if my DPF is clogged? 

Fault codes such as “too frequent of regens” or “DPF differential pressure high” are good indications that your filter may be clogged or in need of cleaning. 

What are some common mistakes with DPF maintenance? 

High idle times are the largest contributor to premature DPF cleanings and failures. 

How long should a DPF filter last? 

Based on idle times, fuel usage and application, the average filter needs to be cleaned around 250,000 miles and replaced around 500,000 miles. Keep in mind that these are estimates and it will vary by filter. 

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