2026-04-30 · By the Auto Trends technicians
The Cummins B-series is one of the most respected diesel engines on the planet, and its reputation comes from the 5.9-liter that ran from 1989 to mid-2007. The 6.7 replaced it in 2007.5 to meet new emissions standards — adding a particulate filter, an EGR system, and (later) a DEF / SCR system to reduce NOx.
From a customer’s perspective, those changes matter. The 5.9 has nothing to delete, no DPF to clean, no DEF tank to refill, no NOx sensors to replace. It’s a comparatively simple engine. The 6.7 has all of that — and the systems work, but they’re additional points of failure.
Strengths: mechanical simplicity. The early 24-valve trucks (1998.5–2002) used a Bosch VP44 injection pump that’s well-understood and not expensive to replace. The later 24-valve trucks (2003–2007) used a CP3 high-pressure pump that’s bulletproof. Lift pumps, injectors, head gaskets are all known quantities with strong aftermarket support. A 5.9 with 300,000+ miles is common.
Weaknesses: the early 24-valve VP44 pumps fail; expect to replace one in the truck’s life. The 24-valve cylinder head has a known issue with the “killer dowel pin” (KDP) which can drop into the timing case if not addressed — we tab the dowel during any major service. Power output is modest by modern standards (235–325 hp depending on year and trim).
Repair costs: generally lower. Parts are abundant, labor is straightforward, and the engine is mechanically simple. A typical injector job runs $1,500–$2,500. An entire engine rebuild is in the $8,000–$12,000 range.
Strengths: more power (350–420 hp), better towing torque, modern transmission options (Aisin AS69RC for HD applications), and the truck itself is more refined. Plus, used trucks are far more available — the 5.9 hasn’t been built in 17 years and prices have actually gone up as supply tightened.
Weaknesses: the emissions systems add complexity. The DPF needs to regen periodically (active regen happens automatically; passive regen happens during highway driving). The DEF system needs fluid topped off and the tank header occasionally serviced. NOx sensors fail. And the early 6.7s (2007.5–2012) had injector issues that have largely been resolved on later trucks but show up on used purchases.
Repair costs: higher. A NOx sensor replacement is ~$400 per side. A DPF cleaning service is $350–$600. Injectors on the 6.7 are not significantly more expensive than the 5.9, but the labor is harder. An entire engine rebuild is in the $12,000–$18,000 range.
We see customers in three buckets:
1. “I want to do my own work.” Buy a 5.9. The aftermarket and DIY support is unparalleled. Parts are everywhere. The engine is forgiving of beginner mistakes. Years of YouTube content cover every common job.
2. “I want a daily driver / occasional tower.” Either works. The 6.7 is more comfortable and quieter; the 5.9 is more characterful. Buy the truck that’s in better condition, not the engine.
3. “I tow heavy and put on serious miles.” Buy a 6.7 with the Aisin transmission (HD trucks). The combination of modern power output, transmission durability, and emissions-compliance for heavy work is hard to beat. Budget for the emissions service costs as part of ownership.
If you’re tempted to delete the emissions on a 6.7 to “make it like a 5.9,” don’t. (1) It’s federally illegal and Colorado has been actively enforcing. (2) You lose 30–50% of resale value. (3) You can’t sell or register the truck in any state with emissions inspection. (4) Long-term reliability of deleted trucks is actually worse, not better, because the ECM was never tuned for that configuration. We don’t perform deletes and we don’t service deleted trucks for emissions-affecting work.
If emissions complexity is genuinely the issue, just buy a 5.9. There are still plenty of clean ones on the market.
For a daily driver / weekend tower / shop truck, our techs lean toward 2003–2007 (5.9 24-valve, CP3 pump, before emissions complexity). The truck is simple, reliable, and parts are cheap. For heavy towing and modern comfort, a 2014+ 6.7 with the Aisin transmission is the sweet spot.
Most diesel techs we know say 2003–2007 (5.9 24-valve, CP3 pump). The fuel system is reliable, the engine is mature, and there’s no DPF / DEF complexity. The 2014+ 6.7 with Aisin transmission is the modern equivalent.
Generally no. The truck can’t be registered legally in many states. Resale is much weaker. And if you ever need to bring it back to stock, the cost is significant. If you find a deleted truck you love, plan for the cost of un-deleting before purchase.
The 2019+ 6.7 HO Cummins (in RAM 3500 with the AS69RC Aisin) is the most powerful Cummins ever in a pickup — 400 hp, 1,000 lb-ft. It’s also a more sophisticated engine with tighter tolerances. Parts costs are higher when something fails. For heavy commercial use it’s excellent. For light-duty it’s overkill.
With reasonable maintenance, both engines easily go 300,000+ miles. We see 5.9s past 500,000 still running on the original head gasket. The Cummins B-series is one of the most durable diesel engines ever built.
Yes — see our Cummins repair page. We have the right scan tools (Cummins INSITE) for both generations and we keep parts on the shelf for the most common jobs.
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