DPF Regen Failing Explained
Diesel Particulate Filters (DPFs) have been around since 2007. By now everyone understands that there are mainly two types of regen events that are run. One is passive, which means that the DPF is cleaning itself - much like a self-cleaning oven - while you are driving down the road through heat built indirectly in the system. The other is an active regen event, which means the vehicle is injecting fuel into the exhaust system to create high temperatures. One variation of the active regen is the “parked regen.” This is where the driver or technician presses a button while the vehicle is stationary to perform an active regeneration.
However, sometimes even the parked regeneration doesn’t work, and you need to use a diagnostic tool to “force” the DPF regen. The problem is that this often doesn’t work as well. Various software packages may or may not explain why forced regeneration fails. This blog post will give you some common checks that you can do.
Dash Switches & Pedals In Wrong Position
A common cause for a DPF regen failing is that the software you’re using isn’t clearing the vehicle as “safe.” The following conditions must be met for the software to clear the vehicle or else the vehicle cannot initiate regeneration:
- Parking brake is set
- Clutch is not pressed in
- Accelerator pedal is not pressed in
- Vehicle is in neutral
- Vehicle speed is zero
Once you’ve confirmed these qualifications, check your software to view the live data to ensure that a faulty clutch switch or accelerator pedal is not showing the electronic control module (ECM) they’re engaged when they’re not.
PTO & Idle Switches are ON
Check the PTO and idle switches in the dash. If they are “on,” they must be turned “off” to prevent the DPF regen failing.
Air Conditioning is OFF
This doesn’t apply to all manufacturers and engines, but often having the air conditioning ON - even at the lowest setting - will trigger a DPF regen failing. This is because the engine and cooling fans can create a cooling effect that won’t allow the engine to generate enough heat for regeneration temperatures. Engine cooling fans that are stuck on can also cause lead to a DPF regen failing.
Derate Codes are Present
One common cause for a DPF regen failing is an active derate code. On many vehicles, you can NOT run a regen when a derate code is active.
Look carefully at what fault codes your diagnostic tool is showing. The ECMs on commercial truck engines will set a code that specifically states the vehicle is derated. These codes are only set with other fault codes logged for a period of time. (For example, P1495 and P1496 are common derate codes on PACCAR MX engines.)
You must fix the original fault code first, then run a de-rate disable command in your diagnostic software. Only after this is completed can you run a regen command without the DPF regen failing.
Some manufacturers and engines require the soot level to be above a certain percentage for a stationary/forced regeneration to occur. This is usually more of a problem in earlier year model truck engines (mainly EPA2007 engines), but has been seen in later years as well. If this is the case, you can try to run the vehicle at a high idle state long enough to create enough soot.
Other Active Fault Codes
Your truck engine ECM is built to protect the engine. Many fault codes, when active, will not allow you to perform a regen. This is another common cause for a DPF regen failing. We highly recommend you check all your active fault codes in Diesel Repair to see if that code is preventing the DPF regeneration from starting.
If you’ve completed these basic checks and still find your DPF regen failing, take a look at this video:
Still having problems?
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