At The DPF Team, our core expertise lies in the precise and professional removal of emission systems, including DPF, EGR, and AdBlue. We work meticulously to ensure that after these modifications, a vehicle performs reliably, cleanly, and without triggering fault codes or causing long-term damage. Our work should not diminish the value of our clients’ assets.

However, a growing and concerning trend has emerged. We are increasingly seeing vehicles that have had their emission systems “deleted” by less knowledgeable operators, leading to a host of complex and expensive problems. These vehicles often arrive at our partner workshops or direct to us with symptoms that are confusing, intermittent, and difficult to diagnose.

This article aims to help you, our valued partners, identify the tell-tale signs of a botched deletion job. Understanding these scenarios can save you and your customers significant time, money, and frustration.

Common Symptoms of a Poorly Executed DPF/AdBlue Deletion

When a deletion is not performed with the due care and technical precision it requires, the vehicle will often exhibit one or more of the following issues:

1. The Phantom DPF: Persistent System Messages

• • The Symptom: The vehicle’s dashboard continues to display DPF-related warnings or messages, even though the physical DPF has been removed and the system was supposedly “tuned.”

• • The Cause: This indicates an incomplete or incorrect firmware modification. The Engine Control Unit (ECU) has not been properly instructed to ignore the removed component, leading it to believe a fault exists.

• • The Diagnosis: Typically this one of the easier scenarios to identify, as the symptom directly points to unresolved firmware flags.

2. The Silent Limp Mode: No Power, No Fault Codes

• • The Symptom: The vehicle experiences a significant and persistent loss of power, yet no Diagnostic Trouble Codes (DTCs) are stored, and no warning lights are illuminated. A real-world example involved a 2013 Mitsubishi Fuso we worked on that would not log codes even when critical sensors like the MAF or boost sensor were disconnected.

• • The Cause: The ECU’s fault-handling protocols have been severely compromised by a bad calibration. It can no longer properly monitor system parameters or trigger the appropriate fault responses, leaving the vehicle in a permanent, silent limp mode. 

• • The Diagnosis: This is a particularly dangerous scenario, as it can mislead technicians into replacing major components when the root cause is a bad dpf calibration map. In the case of this fuso the partnering workshop had replaced the entire engine and became sure something else was going on.  

3. Excessive Black Smoke

• • The Symptom: The vehicle emits excessive, highly visible black smoke from the exhaust.

• • The Cause: A professional deletion should not result in smoke if the vehicle’s fuel system is in good order. Emission systems are designed to trap and neutralize particulate matter which are often invisible to the eye. Huge plums of black smoke after a deletion can be a clear sign of a poor calibration. We corrected this on a 2015 Toyota Hiace 1KD, where a bad firmware change was the sole culprit.

• • The Diagnosis: We asked the customer to see fuel systems specialists but he came out straightforward with transparency on what they had recently been done. More often customers are not very transparent for fear of charge or outright decline. Subsequent investigation did confirm the bad changes to ecu.

4. Periodic White Smoke and Engine Damage

• • The Symptom: The vehicle produces periodic white smoke and suffers from rapid oil degradation, which can lead to catastrophic engine failure. We encountered a GLE350d that destroyed three engines in 13 months due to this issue.

• • The Cause: This occurs when the software instructions for a forced regeneration are not properly disabled. The ECU continues to command post-injection cycles, dumping raw fuel into the exhaust stroke. This fuel dilutes the engine oil, destroying its viscosity and lubricating properties, ultimately leading to engine seizure.

• • The Diagnosis: A severe and destructive failure that points to a deeply flawed calibration affecting core engine functions. In this case customer knew the vehicle’s history. He had owned it for years prior and the issues only started after removal of emissions.

5. Intermittent and Unexplained Power Loss

• • The Symptom: The vehicle drives normally at first but will intermittently and unpredictably enter a limp mode with no warning lights or smoke. This was the case with a Landcruiser 200 series we diagnosed.

• • The Cause: The modified ECU software is tripping over latent or incorrectly mapped parameters. Certain driving conditions or sensor readings trigger a fault state that isn’t properly communicated to the dashboard, leaving the driver and technician with no data to work with.

• • The Diagnosis: This we admit is an extremely difficult scenario. Its difficult to trace without a known history of modification, potentially leading to unnecessary replacement of turbos or other engine components.

Why Correcting These Issues is So Complex

Our work is often perceived as simple, but the reality is far more complex. Allow us to offer an analogy:

Think of a vehicle’s ECU software not as a single page of instructions, but as a 1,000-page book written in machine code (binary/hexadecimal). Our task is to find and correctly modify just 60 specific paragraphs, scattered across 20 different chapters, that relate to the emission systems.

Furthermore, every vehicle with different options and features has a different version of this book—it could be 1,100 pages with entirely new chapters. No two are ever identical, some of our partners have experienced first hand for example; we do one car this week for you next week we tell you another identical one cannot be done. Sound familiar? This would mainly happen on the very latest models. Months later this however changes. 

When we are presented with a vehicle badly done by these operators, our first job is to diagnose what was altered in this 1,000-page book, often without an original copy for reference. Figuring out which pages were incorrectly edited and how to restore them is a painstaking process that demands significant time, expertise and patience. In some cases other modules such as transmission my have received a share of changes as some vehicles limp strategies work with gearbox. Compounding this, the vehicle may have already sustained physical damage from the bad firmware, a problem that may only manifest later.

Our Policy on Correction Work

Due to the immense complexity, unpredictable timelines, and potential for underlying damage, The DPF Team has made a strategic decision to phase out correction work on vehicles previously modified by other operators.

Starting in January 2025, we began limiting this work, and we are now actively discouraging our partners from taking on these “can of worms” type of jobs. It is exceptionally difficult to provide an accurate quote or turnaround time for a vehicle with an unknown and potentially botched modification history.

A clean slate is always preferable. It is far easier, more reliable, clear timelines and more cost-effective for everyone involved to work on a vehicle whose systems have never been tampered with. We also manage reputation risk especially from customers with vehicles that become “can of worms”

Partner with Confidence

Trust The DPF Team for professional, reliable, and clean emission system work from the start. If one of your customers is considering a deletion, steer them toward a professional solution to avoid these costly and dangerous scenarios. For vehicles that have already been poorly modified, we advise extreme caution, as the path to a reliable fix is often long, expensive, and uncertain.

For any new work or consultations, please do not hesitate to contact us.