For transit fleets, aftertreatment surprises mean road calls, missed pull-outs, and expensive parts swaps. One frequent culprit: partial Diesel Oxidation Catalyst (DOC) face plugging that quietly slows DPF warm-up until the filter overloads. In this case, WatchTower, Diesel Laptops' predictive maintenance tool for transit buses, caught the problem days before any fault code, so maintenance could fix the root cause and avoid a failure. Here's how predictive AI plus human diesel technicians made the difference.

The Problem: Hidden Aftertreatment Risks in Transit Duty Cycles

Transit duty cycles create perfect conditions for aftertreatment trouble. This includes stop-and-go patterns, variable loads, and frequent regenerations. When the DOC begins to face-plug, the DPF struggles to reach regeneration temperature, pushing soot loading higher and raising failure risk. The worst part? The ECM often won't warn you early enough to prevent downtime.

What this means operationally: more road calls, derates, and vehicles out of service at the worst possible time. WatchTower provides transit fleet monitoring with AI plus expert review and repair plans so this doesn't happen.

The Approach: Predictive AI + Expert Review, Not Just Thresholds

Simple thresholds on temperature or pressure miss early-stage trends. WatchTower instead analyzes regeneration profiles and inlet temperature behavior across context to spot anomalies that point to DOC face plugging. Every alert is then validated by a Master Technician, who issues the recommended repair and confirms the label ("true"; vs "false"), creating a continuous feedback loop that boosts accuracy over time.

Data inputs used: inlet/outlet temperatures, pressures, engine speed, and regeneration states all captured while the bus is operating, not just in the bay.

The Result: Actionable Detection Days; Weeks In Advance

In this case, WatchTower identified partial DOC face plugging early by detecting a slower-than-normal DPF warm-up during regens before any fault codes appeared. Across deployments, fleets typically see detection ~5 days in advance, up to 30 days, and a 91% true positive rate on repair plans. This means when we say to act, you can trust it.

Why it matters: catching DOC plugging early prevents DPF overloads, avoids unplanned downtime, and reduces material costs. These outcomes echoed on our WatchTower page (fewer road calls, faster diagnostics, lower costs).

 

What we looked for:

• Regen warm-up time: abnormally slow temperature rise at DPF inlet.
• Outlier detection vs. vehicle’s normal profile: flagged as likely DOC face plugging before escalation.

How to Apply This in Your Fleet

We provide an easy path to enable this technology to be tested in your fleet:

1. Start with monitoring + baseline: Connect vehicles and let WatchTower establish normal regeneration and temperature patterns per asset and route.
2. Act on expert-validated alerts: Your team gets human-reviewed alerts and step-by-step repair plan. No more guessing for your technicians.
3. Measure results in 30-60 days: Track road calls avoided, diagnostic time saved, and material cost reduction. Transit agencies have reported up to 24% material cost reduction and around 50% faster diagnostics.

Why Not Just Use Fault Codes?

Because they're often late. In both DOC and DPF failures, we routinely detect the trend days before the ECM throws a DTC. Giving you time to plan, schedule, and fix before it becomes a service disruption.

Ready to See WatchTower in Action?

If you manage a transit bus or coach fleet and want to get ahead of aftertreatment failures, diesel aftertreatment monitoring with predictive AI may be right for you. We'll model your fleet, connect a pilot, and show you what predictive maintenance looks like with AI and expert diesel technicians behind every alert. Fill out this form, and we'll also send you a case study so you can see WatchTower in action and learn how real fleets are reducing downtime before failures occur.