P20EE: SCR NOX Catalyst Efficiency Below Threshold
P20EE is a powertrain diagnostic trouble code in the the manufacturer's own system grouping group. Our vehicle database stores it against 3 models.
What P20EE actually means
P20EE is not on the shared SAE J2012 list: it is a manufacturer-specific code, so its definition comes from the maker’s own service documentation rather than the standard numbering scheme. Our vehicle database stores it against 3 models.
The stored definition for P20EE is “SCR NOX Catalyst Efficiency Below Threshold”. The first character of the code identifies the system — Powertrain in this case. The second character tells you who defined the code: this one is a manufacturer-specific code. Reading the code that way matters: a manufacturer-defined code means the test and its causes are the maker’s own, so the list below is narrower by design and generic code references will not define it.
Within that system, P20EE sits in the the manufacturer's own system grouping group. That is the part of the vehicle the control module was watching when it set the code — the subsystem this code belongs to — and it narrows down enormously where a technician will start looking. Manufacturer-specific codes are worked with the maker’s own service procedure, so the factory test routine matters more than generic advice.
How serious is P20EE?
We rate P20EE as Moderate — diagnose soon. That rating comes from the severity recorded in our database for this code, not from how alarming the name sounds.
A moderate-severity code usually leaves the vehicle drivable, but the underlying fault tends to worsen and can cascade into a more expensive repair. It is reasonable to drive cautiously to a workshop in the near term, but the code should be diagnosed rather than cleared and forgotten.
Most likely causes of P20EE
Our database records 2 causes for P20EE, ranked by how many of the 3 models that log this code report each one.
DEF system / catalyst degradation — the most widely recorded cause, appearing on 2 of the 3 models. DEF system degradation — logged by a single model in our database.
Causes are listed as recorded in the database. The same code can have different root causes on different vehicles, so the ranking is a starting order for diagnosis rather than a diagnosis in itself.
How a technician diagnoses P20EE
Manufacturer codes are worked with the maker’s own service procedure, so the factory test routine matters more than generic advice. Confirm the code is active rather than historic, then work through the ranked causes from cheapest and most likely to most intrusive. In practice that means:
How a technician works P20EE — decision path
Powertrain codes respond to data. Capture the freeze frame, then work through the ranked causes from cheapest and most likely to most intrusive.
- Confirm the code is active and capture freeze-frame dataThe snapshot recorded when the code set holds the engine speed, load, coolant temperature and fuel trims at that moment — often the single most useful piece of evidence for separating one candidate cause from another.
- Compare live data against the freeze frameRe-create the conditions from the snapshot and watch the relevant sensors live. A value that cannot reach the expected range narrows the search immediately.
- Work the ranked causes from cheapest and most likelyThe list on this page is ordered by how many of the recorded vehicles show each cause. Start at the top: an intake leak, a dirty sensor or a worn cap is far more common than a failed assembly.
- Repair the confirmed cause, then re-check the monitorsFix what the evidence actually points at rather than replacing parts speculatively — a misfire or lean code will re-set if the real cause is still present.
- Clear the code and complete a full drive cycleClearing alone proves nothing. The code must stay clear through a drive cycle that reproduces the original conditions, and the readiness monitors must run again.
If a workshop replaces a component for P20EE without showing you the measurement that condemned it, ask for the data. On a the manufacturer's own system grouping code, the recorded causes are usually testable, so a diagnosis should be demonstrable rather than asserted.
What drives the cost of fixing P20EE
We deliberately do not print a single repair price for P20EE. The parts bill depends entirely on which recorded cause is confirmed. The honest answer is that the cost is set by which cause is actually present, and that range is wide — a repair for the first cause listed above and the last can differ by more than an order of magnitude in parts alone: the confirmed cause moves the bill more than any other variable. Add regional labour rates and the spread becomes wider still.
The factors that actually move the number, in rough order of impact:
- Sensor or module. Whether the confirmed cause is a sensor or a control module is the first thing that moves the bill, and on manufacturer-specific systems the pricing is the maker’s own.
- Access. Access varies more on manufacturer-defined systems than on standard ones, because the component placement is not shared across models.
- Dealer-network parts. Some manufacturer-specific components are only available through the dealer network, which removes the aftermarket option from the comparison.
- Diagnosis billed separately. Manufacturer codes are worked with the maker’s own procedure, so the diagnostic step takes the time it takes.
The practical approach: get the cause confirmed first, then collect two or three written quotes for that specific repair. To judge whether the repair is worth doing against the value of the vehicle, use our repair-or-replace decision guide.
Vehicles in our database that log P20EE
Only 3 models in our database record P20EE, so the list below is short but specific. The makes appearing most often are Chevrolet (1), GMC (1), Ram (1). Each model links to its own guide, where this code appears alongside that vehicle's full fault list and running costs.
Frequently asked questions about P20EE
Is P20EE a generic OBD-II code?
No. P20EE is a manufacturer-specific code, so it does not appear on the shared SAE J2012 list and generic code references will not define it. Its meaning comes from the manufacturer’s own service documentation, which is also why the causes listed on this page are narrower than for a generic code.
Is it safe to drive with P20EE?
Severity for P20EE is rated medium in our database. A moderate-severity code usually leaves the vehicle drivable, but the underlying fault tends to worsen and can cascade into a more expensive repair. It is reasonable to drive cautiously to a workshop in the near term, but the code should be diagnosed rather than cleared and forgotten.
What are the most common causes of P20EE?
In our vehicle database, the causes recorded for P20EE are: DEF system / catalyst degradation; DEF system degradation. They are ranked on the page by how many of the 3 vehicles that log this code list each cause.
How much does it cost to fix P20EE?
We do not publish a single figure for P20EE because the real cost depends entirely on which cause is present — a repair for the cheapest cause on the list and the most expensive one differ by an order of magnitude, and labour rates vary by region. The page explains which factors drive the cost and recommends collecting written quotes before authorising work.
Which vehicles commonly report P20EE?
Our database stores P20EE against 3 vehicles, most frequently from Chevrolet (1), GMC (1), Ram (1). The full list is shown on this page and each model links to its own cost and fault guide.
Related codes and next steps
Codes that share the same system group often appear together, because a single fault can set more than one:
For the full list, see the OBD-II fault code cross-reference. If the repair cost is what you are weighing, model the total with our total cost of ownership calculator before deciding, and check whether an open safety recall covers the fault with the recall lookup.
Sources and scope
Code definitions follow SAE J2012 / ISO 15031-6 naming. The descriptions, listed causes, and severity ratings on this page are the values stored in the VehCalc vehicle database (snapshot 2026-08-20) for the models listed above. Codes and causes vary by model year and engine.
Diagnostic reference only — not repair advice. This page is provided for educational and planning purposes and does not replace an inspection by a qualified technician or the manufacturer's service information. Before repairing a vehicle you depend on, confirm the diagnosis with an ASE-certified mechanic.