A full-length read on a 2018 Ram 2500 Cummins with P20EE.
This is what a TorqueTrace preliminary report actually looks like end to end — vehicle summary, plain-language problem summary, ranked likely causes with confidence, urgency, OBD-II interpretation, recommended shop checks, and the handoff note. The content below is a fully worked example. Your report will use the same shape, tuned to the year, make, model, symptoms, and OBD-II codes you submit.
What the truck is — the build context that shaped this read.
What was reported, restated so you can read it on the sidewalk.
Active regens have been triggering roughly every 120 miles since a DEF refill last month, and the truck has thrown an intermittent P20EE (reductant efficiency low, bank 1). Under heavy tow the engine briefly cuts power but no limp mode has latched. No active check-engine light on cold start, no visible smoke, no fuel-system codes. The pattern is consistent with a post-SCR system slowly losing conversion efficiency, not a hard failure yet.
Synthesized from: vehicle build context, the owner-written symptom set, the scan-tool readout (one stored code, P20EE), and a live-noise self-check.
From most plausible down — each one with a confidence flag.
Causes are ordered by how well the cluster of symptoms and scan data fits each explanation on its own. Two independent sensor signals aligning with a single component is the strongest pattern in this report.
Degraded SCR catalyst — most common at this mileage band.
On the 2013–2018 6.7L Cummins XCP, the SCR catalyst begins to lose conversion efficiency between roughly 110k and 140k miles, especially with frequent short trips or extended idle time. A degraded catalyst explains both the shortened regen interval AND the bank-1 P20EE, because the post-SCR NOx sensor sees elevated tailpipe NOx while the pre-SCR reading stays in range. Confidence is MEDIUM-high because two independent sensor signals line up with a single component.
Stuck or internally leaking DEF injector — the cheap-to-fix alternative.
A DEF injector that dribbles instead of atomizing will produce urea crystals on the SCR face, which looks identical to catalyst degradation from the NOx sensors. This is the FIRST thing a credible shop will rule out because replacing a DEF injector is far cheaper than a catalyst. If the post-SCR NOx drops to near-zero during a commanded injection but rises again when the injector is commanded off, the injector is the cause, not the cat.
NOx sensor drift on bank 1 — possible, but does not explain the regen interval.
A drifting post-SCR NOx sensor can throw P20EE on its own. If the regen interval were unchanged this would be the prime suspect. Because the regen interval is also shortened, a sole sensor-fault read is less likely. It still belongs on the shop's checklist because replacing a NOx sensor first and then discovering the cat is also tired is a common miss.
Whether to drive it, when to book, and how to plan the next stop.
Drivable. No active limp mode, no smoke, no warning beyond the stored P20EE. Confirm it is safe to drive through the next regen cycle, and book a shop visit within the next 2–4 weeks — not an emergency tow, but also not something to ignore across a multi-day tow haul.
What the stored trouble code actually means, in plain language.
Reductant Efficiency Low (Bank 1)
P20EE means the engine computer is comparing NOx readings before and after the SCR catalyst and seeing too little reduction across the catalyst. On its own, P20EE does not point at one component — it describes the symptom of low conversion efficiency. The job of a credible diagnostic is to figure out whether the catalyst is tired, the DEF injector is misbehaving, or the NOx sensor itself has drifted. That is why the in-shop pre- and post-SCR NOx test is the first check, not a parts swap.
What to ask the shop to do, in the right order, before any parts swap.
The list below is ordered for cost and for risk of a premature parts replacement. Share it with the shop before they quote any work.
- 1Share with the shop before any parts quote.
In-shop pre-SCR and post-SCR NOx sensor test
Have the shop capture live NOx values from both sensors during steady-state cruise and during a commanded active regen. A healthy catalyst should show post-SCR NOx well under 50 ppm while pre-SCR holds under 300 ppm. If post-SCR NOx mirrors pre-SCR, the catalyst is exhausted. If post-SCR NOx drops under load but climbs again after a cool-down, the DEF doser is the prime suspect.
- 2Share with the shop before any parts quote.
DEF injector leak-down test
A dealer-level scan tool can command the DEF injector to fire a fixed volume and watch the downstream delivery rate. Compare against spec; a dribbling injector will show a delivery curve that starts high and falls off. Also have the tech visually inspect the SCR inlet face for urea crystal build-up — heavy crystal coverage points at injector dribble rather than cat aging.
- 3Share with the shop before any parts quote.
DEF quality and level verification
Pull a DEF sample and check concentration with a refractometer (target 32.5% urea). Contaminated or diluted DEF will trigger P20EE even with a healthy catalyst and injector. Also verify the level sensor — a phantom full reading from a faulty level sensor can produce over- or under-dosing.
- 4Share with the shop before any parts quote.
Active regen observation
Ask the shop to command a parked active regen and watch tailpipe temperature, post-SCR NOx, and DPF differential pressure. A regen that completes in normal time and brings DPF pressure back to baseline rules out a secondary DPF restriction — which matters because a restricted DPF will drive more frequent regens even with a perfectly healthy SCR.
- 5Share with the shop before any parts quote.
ECM reset and recheck after any repair
After a DEF injector replacement (or any NOx sensor swap), clear the P20EE with a dealer-level scan tool and run the truck through normal driving for at least two regen cycles. If P20EE returns within one regen cycle, the underlying catalyst is the next stop — do not chase sensor replacements past the first legitimate fix.
- 6Share with the shop before any parts quote.
Final: do not replace the SCR catalyst first.
It is the most expensive component in the diagnosis and the one most often replaced prematurely. A competent shop will only quote an SCR catalyst replacement after the DEF injector and NOx sensors have been definitively ruled out.
The handoff — what to bring into the shop and what to expect.
Take this to a qualified mechanic. TorqueTrace is a credible first-pass read you can take to your shop — it is not a substitute for an in-person inspection, scan-tool data, or for the judgment of a technician who can put hands and a lift on the truck. Walk the mechanic through the causes ranked above and ask them to start with the DEF injector and live NOx test, not with a SCR catalyst quote.
Operating-principle caveat · read before acting on this report.
TorqueTrace is preliminary guidance, NOT a diagnosis. Use it as a smarter starting point for a shop conversation. If a brake warning, steering pull, fluid leak, smoke, or hybrid high-voltage warning is present, stop driving and contact a qualified mechanic first.
- Brake warning, soft pedal, grinding, or fluid leak.
- Steering pull, hard steering, or visible front-end fluid leak.
- Smoke from engine bay, exhaust, or under the vehicle.
- Hybrid or EV high-voltage battery warning light.
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