P20EE
SCR NOx Catalyst Efficiency Below Threshold Bank 1P20EE is a generic OBD-II powertrain diagnostic trouble code: SCR NOx Catalyst Efficiency Below Threshold Bank 1. It is logged by the engine control unit when the scr/adblue monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P20EE means
P20EE is a generic OBD-II diagnostic trouble code that sets when the engine control module determines that the Selective Catalytic Reduction (SCR) catalyst on Bank 1 is not reducing oxides of nitrogen (NOx) as effectively as the calibration requires. The ECU monitors NOx levels using sensors placed before and after the SCR catalyst and compares the conversion rate to a stored threshold. When the measured efficiency stays below that threshold across one or more drive cycles, P20EE is stored and the malfunction indicator lamp is illuminated.
SCR systems inject Diesel Exhaust Fluid (DEF, a urea-water solution) into the exhaust upstream of the catalyst, where it reacts with NOx to form nitrogen and water vapour. Because the code reflects an end-result measurement, the underlying fault is rarely the catalyst itself; it is more commonly a problem with the DEF dosing system, NOx or exhaust temperature sensors, wiring, or upstream exhaust leaks that disturb the SCR reaction.
P20EE almost always sets alongside other DEF/SCR codes that point to the real root cause. On many vehicles a confirmed P20EE eventually triggers a no-start countdown to enforce emissions repair.
Common causes
Most-frequently reported root causes when P20EE is logged.
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1
Low, contaminated, or incorrect DEF (urea) fluid
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2
Faulty DEF dosing injector or supply pump
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3
Failed upstream or downstream NOx sensor
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4
Faulty exhaust gas temperature sensor in the SCR circuit
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5
Damaged wiring or corroded connectors in the SCR/DEF harness
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6
Exhaust leak upstream of the SCR catalyst
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7
Aged or contaminated SCR catalyst substrate
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8
Outdated engine/SCR control module software
Symptoms drivers notice
How to diagnose P20EE
A typical diagnostic flow when this code is present.
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1
Scan all modules and record every stored and pending code; address any DEF dosing, NOx sensor, or exhaust temperature codes before chasing P20EE itself.
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2
Verify DEF level, quality, and concentration; confirm the correct fluid is being used and that the tank is not contaminated with water or fuel.
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3
Inspect the exhaust system from the turbo to the SCR for leaks, cracks, or loose clamps that could let untreated gases bypass the catalyst.
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4
Use live data to compare upstream and downstream NOx sensor readings during a known good drive cycle and check exhaust gas temperature sensor values for plausibility.
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5
Command a DEF dosing test with a capable scan tool and confirm the injector sprays, the pump builds pressure, and the lines are not blocked or crystallised.
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6
Inspect SCR and DEF wiring/connectors for chafing, corrosion, or water ingress; repair as needed and clear codes.
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7
Only after upstream faults are ruled out, evaluate the SCR catalyst itself and check the manufacturer for any applicable software updates or technical service bulletins.
Vehicles where we've handled P20EE
Platforms in our catalogue with confirmed P20EE coverage.
Related powertrain codes
- B0001 — PCM Discrete Input Speed Signal Error
- B0004 — PCM Discrete Input Speed Signal Not Present
- C0359 — Four Wheel Drive Low Range (4LO) Discrete Output Circuit
- C0362 — 4LO Discrete Output Circuit High
- P2000 — NOx Adsorber Efficiency Below Threshold Bank 1
- P2001 — NOx Adsorber Efficiency Below Threshold Bank 2
Frequently asked questions
Can I keep driving with a P20EE code?
Short trips to a workshop are usually fine, but the vehicle may enter reduced power mode and many diesels start a no-start countdown for emissions faults. Do not ignore it.
Does P20EE always mean the SCR catalyst is bad?
No. The code reports low conversion efficiency, but the catalyst itself is rarely the cause. DEF quality, dosing issues, sensors, and exhaust leaks are far more common.
Will topping up or changing the DEF fluid clear P20EE?
If the previous DEF was low, old, or contaminated, refilling with fresh fluid of the correct specification can resolve the fault once the codes are cleared and the system re-tests.
Why do other codes show up with P20EE?
P20EE is an outcome code based on NOx measurements. Faults in NOx sensors, the DEF dosing system, or exhaust temperature sensors typically set their own codes first and should be diagnosed before condemning the SCR catalyst.
Disabling P20EE in software
RaceTune can permanently disable P20EE — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECUs with a P20EE disable in our catalogue
Confirmed coverage from our recipe database — we support many more families. Upload your file and our identifier will match it automatically.
- Bosch EDC17C60 verified 2 software versions
- Bosch EDC17C74 verified 2 software versions
- Bosch EDC17CP57 verified 2 software versions
- Bosch EDC17C56 verified 1 software version
- Bosch EDC17C66 verified 1 software version
- Bosch EDC17CP44 verified 1 software version
- Bosch MD1CP002 verified 1 software version
- Bosch MD1CP004 verified 1 software version
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
Got P20EE in your scan?
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