P20EE on a 2017-2018 Ram 2500/3500 6.7L Cummins: Check Software and DEF First
JC Landry, ASE Master TechnicianPublished Oct 26, 2026 · Updated Oct 27, 2026
P20EE means the PCM sees the SCR catalyst removing less NOx than it expects on a 2017-2018 Ram 2500 or 3500 with the 6.7L Cummins. Start with the PCM software, then DEF leaks and quality, then the exhaust and the decomposition tube, then the injector flow test; the catalyst is replaced only when the flow test points to it. A speed or power limit can follow if the fault is left alone, so do not let it sit.
Safety first
- DEF is highly corrosive. If it gets on the DEF pump wiring connector, replace the DEF tank wire harness.
- If you use a torch on the exhaust, keep flame away from the fuel lines and tank; it can be fatal.
- On the intermittent check with the engine running, stay out of line with the fan, keep hands off belts and pulleys, no loose clothing.
What does P20EE mean on a 2017-2018 Ram 2500/3500?
P20EE (SCR NOx Catalyst Efficiency Below Threshold - Bank 1) is the PCM telling you the SCR catalyst is not converting enough NOx. The DEF injector on the decomposition tube sprays diesel exhaust fluid (a urea solution) ahead of the catalyst, where it turns into ammonia that the catalyst uses to convert NOx into nitrogen and water. The DEF dosing control unit (DCU) runs the system, and the PCM varies the spray by pulse width modulation.
Two NOx sensors judge the catalyst. The upstream sensor (1/1) at the turbocharger elbow downpipe reads NOx going in; the downstream sensor (1/2) at the catalyst outlet reads NOx coming out. The PCM compares the two to work out efficiency.
The PCM sets P20EE when it detects NOx conversion across the catalyst lower than expected. The monitor gathers NOx data across varying engine speeds and loads, makes a pass or fail decision and starts over. A steady highway drive covers the conditions it needs. Weak DEF, a bad spray, an exhaust leak or a spent catalyst all fail the check.
Several related codes matter here:
- P1C54 (SCR NOx Catalyst Missing) uses the same kind of set condition. When pending or active it brings a chime and a "Service DEF System See Dealer" message, then a countdown to a 5 mph speed limit that does not clear until the diagnostic passes or the PCM is recalibrated.
- P2201 and P229F are NOx sensor circuit performance (bank 1 sensors 1 and 2), P22FC is sensor 2 slow response, P207F is reductant quality and P20E8 is reductant pressure too low.
What symptoms does P20EE cause on the Ram 2500/3500?
- Check engine light.
- A speed or power limit can follow if the fault stays unresolved.
What causes P20EE on the Ram 2500/3500, most likely first?
Seven things can drag SCR efficiency down.
| Rank | Cause | Quick confirm | Typical fix |
|---|---|---|---|
| 1 | PCM software out of date | Scan tool shows a newer flash | Flash the PCM, clear the code, test drive |
| 2 | Degraded, diluted or incorrect DEF | Refractometer about 32.5 percent; paper stays light blue; fluid clean | Drain and refill with certified DEF; hydrocarbons mean a new tank, supply pump assembly, injector, supply tube, fill tube and cap |
| 3 | DEF leak in the dosing system | Prime test; check injector, connectors, heater line, supply pump | Repair or replace the leaking part |
| 4 | Exhaust system leak | Look over the whole exhaust | Repair the leak |
| 5 | DEF deposits in the decomposition tube | Pull the injector, look into the tube | Clean the deposits out |
| 6 | Malfunctioning DEF dosing (injector, supply line, supply pump) | Six minute override test: 85 to 115 milliliters is normal; check the line for kinks | Over 115: replace the injector. Under 85: clean debris and retest, then line, then new injector retest, then pump |
| 7 | Defective SCR catalyst | Everything above passes, injector flow 85 to 115 milliliters | Replace the catalyst and the injector gasket |
Chrysler issued tech tip 9003802 for 2016-2017 D2 and DJ trucks (3500 and 2500) naming P20EE, for techs whose call already led to an SCR replacement.
How do you diagnose P20EE on a 2017-2018 Ram 2500/3500?
You will need a scan tool that can run the DEF prime test and doser pump override test, a DEF refractometer, hydrocarbon test paper and a graduated cylinder marked in milliliters. First make sure the scan tool talks to the modules it needs (fix a no-response first) and rule out misfire, hard start, noise or heavy smoke.
- 1
Software, then other codes.
With the ignition on, confirm the PCM has the latest flash. If it does not, flash it, erase the code and test drive under the conditions that set it. If the code stays gone, you are done. If the PCM already had the latest flash, or the code returns after the flash, check for other active codes. Handle every other active NOx sensor and DEF dosing code first, by family:
- NOx sensor circuit and performance: P2201, P2202, P2209, P220A, P220B, P225C, P225D, P225E, P225F, P229E, P229F, P22A7, P22FC
- NOx sensor intermittent: P1C55, P1C56
- NOx sensor communication and data: U029D, U029E, U059E, U059F
- SCR catalyst and SCR error: P1C54, P1C70
- DEF injector and dosing performance: P202E, P2048, P204F, P218F, P249E
- DEF pump and pressure: P208A, P208B, P208C, P208D, P204A, P204C, P204D, P20E8, P20E9, P1E1C
- DEF quality: P206B, P206D, P207F, P2BA9
- DEF level and empty tank: P203B, P203C, P203D, P203F, P2BA7
- DEF temperature and heater circuits: P2043, P2044, P2045, P205C, P205D, P205E, P202B, P202C, P209F, P20B7, P20B8, P20B9, P20BB, P20BC, P21C4
- NOx exceedance and driver inducement: P2BAC, P2BAF
- Dosing control unit power and communication: P21CB, P21CC, U010E, U02A2, U040F, U11C1
If P20EE is active, move on. If it is not active, work it as an intermittent condition.
- 2
DEF leaks, then DEF quality.
With the ignition on, run the DEF prime test, which pressurizes the system. Check the injector and connectors, DEF heater line and supply pump. Repair or replace any leaking part and confirm the repair. Then, with the ignition off, take a sample from the tank itself (not the fill pipe) and look for debris or contamination. The refractometer should read about 32.5 percent. Hydrocarbon test paper in the tank fluid turning from light blue to dark blue means oil or hydrocarbons.
- Fails the refractometer, passes the paper, no other contamination: drain, refill with fresh DEF and confirm the repair.
- Fails the paper or shows other contamination: drain the DEF and replace the tank, supply pump assembly, injector, supply tube, fill tube and fill cap, then confirm.
- In spec and clean: move on.
- 3
Exhaust, then decomposition tube.
Inspect the whole exhaust and repair any leak. If it is tight, disconnect and isolate both negative battery cables, soak the injector bolts with rust inhibitor, wait 5 minutes and pull the injector. Look in the tube for DEF deposits; clean them out and confirm the repair. If it is clear, go on to the flow test.
- 4
Injector flow test, before you replace the injector.
Reconnect the harness and hold the injector in the graduated cylinder. With the ignition on, run the DEF reductant doser pump override test (not the prime test) for the full six minutes until it times out; flow can rise and fall. The spray should be a mist and never drip from the holes. White tip deposits are harmless dry urea, and a bit of residual fluid is no reason to replace it. Then measure:
- 85 to 115 milliliters: replace the injector gasket on reinstall, replace the SCR catalyst, then confirm.
- Above 115 milliliters: replace the injector, then confirm.
- Below 85 milliliters: check for debris. If found, clean it off and rerun the test. If none, check the supply line next.
- 5
Supply line, then pump.
Check the line from the injector back to the pump for kinks or pinching. If it is restricted, replace it and confirm the repair. If it is free, with the ignition off, replace the injector but do not install it in the tube yet; connect it, hold it in a container and rerun the doser pump override test for the full six minutes.
- Still below 85 milliliters: replace the DEF supply pump. Then check the DEF level reads at least 50 percent, run the doser prime override test to completion twice, and test drive at least 15 minutes before checking codes. Then confirm the repair.
- Not below 85 milliliters: install the new injector in the tube with a new gasket. The repair is complete; confirm it.
Get the P20EE tests for your Ram 2500/3500
The software check, DEF tests and injector flow test above follow Ram's own test order. Ask emanuals.ai about your Ram 2500 or 3500 with the Cummins and get the exact test steps, specs and procedures from the factory manual.
Specs you need for the Ram 2500/3500 P20EE repair
| DEF injector bolts | 11 N-m (8 ft. lbs.), with a new gasket |
|---|---|
| SCR catalyst flange nuts | 60 N-m (44 ft. lbs.), with new flange gaskets |
| DEF pump cover bolts | 14 N-m (10 ft. lbs.) |
| DEF type | Mopar Diesel Exhaust Fluid (API Certified) or an equivalent API Certified to ISO 22241; other fluid may damage the system |
| DEF system capacity | 5.5 gallons (21 liters) |
What if the obvious fix does not work?
If the injector sprays 85 to 115 milliliters and everything before it passed, the catalyst is the repair, with a new injector gasket. If it still sprays low with a new injector and a free supply line, the pump is next.
Other suspects: a failing or drifting downstream NOx sensor can report NOx that is not really there, and the PCM reads a weak catalyst. Cheap or diluted DEF can leave deposits. Two common mistakes: replacing the catalyst before ruling out the sensor and dosing side, and clearing the code without finding the cause, which usually returns it after more drive cycles.
How do you confirm the repair?
This is required. Clear the code and reset all memory values with the scan tool. Drive for at least five minutes, with some of it at 40 mph (64 km/h) or faster. During the drive, stop and shut the engine off for 10 seconds or more, then restart and carry on, and make sure the transmission shifts through every gear. After the drive, turn the engine off and read the codes. No code means the repair is complete.
Two more items are required. If the battery was disconnected for any reason (it is for the injector, SCR catalyst and pump jobs), the Battery Reconnection procedure is required. If the PCM was ever replaced, record the injector correlation codes and enter the correct VIN and mileage, or codes will set in the ABS, airbag and wireless control modules.
Questions mechanics ask about P20EE on the Ram 2500/3500
Can you drive a Ram 2500 or 3500 with P20EE?+–
I would not leave it sitting. The sibling code P1C54, which sets on the same kind of conversion shortfall, brings a DEF warning, then a countdown to a 5 mph speed limit that stays until the diagnostic passes or the PCM is recalibrated. A power or speed limit can follow P20EE too if the fault stays unresolved.
What else sets with P20EE on the 6.7L Cummins?+–
Work any other active NOx sensor and DEF dosing codes first. P1C54 uses the same kind of set condition, and the reductant quality code P207F can show up alongside P20EE.
Is there an official record for P20EE on these Ram trucks?+–
Yes. Chrysler tech tip 9003802 covers 2016-2017 Ram 2500 and 3500 trucks. It is a heads-up for techs whose P20EE call has already led to an SCR replacement, and it says Cummins and FCA engineering were investigating the root cause.
Should I replace the SCR catalyst right away on a P20EE Ram?+–
No. The catalyst is replaced only after the earlier checks pass and the DEF injector sprays 85 to 115 milliliters in the six minute test. In that case replace the injector gasket too.
Should you update the PCM software first for P20EE on the 6.7L Cummins?+–
Yes. Confirm the PCM has the latest flash, flash it if not, clear the code and test drive; if the code returns, continue the diagnosis. For 2017 trucks the maker lists a PCM and DCU flash in service bulletin 25-002-17 (built on or before February 22, 2017) and a PCM flash in service bulletin 18-073-17 (built on or before July 31, 2017). For 2018 the PCM flash is service bulletin 18-080-22.
Sources
- Ram 2500/3500 Service & Repair Manual, section DTC-Based Diagnostics, Powertrain Control Module (6.7L Diesel).OEM Manual
- Chrysler GPOP Tech Tip 9003802, "GPOP - Issue Review System", MY16, 17 D2, DJ, 10/18/2017.Service Bulletin
- FCA service bulletin 18-073-17, "Flash: Powertrain Diagnostic and System Improvements", 2017 (DJ) RAM 2500 Pickup and 2017 (D2) RAM 3500 Pickup, August 16, 2017.Service Bulletin
- FCA service bulletin 25-002-17, "Flash: Dosing Control Unit Diagnostic And System Improvements", 2017 RAM 2500 Pickup (DJ) and RAM 3500 Pickup (D2), March 10, 2017.Service Bulletin
- FCA service bulletin 18-080-22, "Flash: Powertrain Control Module (PCM) Updates", 2018 (DJ) RAM 2500 Pickup and 2018 (D2) RAM 3500 Pickup, April 12, 2022.Service Bulletin
- emanuals.ai, Query data, "P20EE Ram 2500/3500".First-Party Data
ASE Master Technician
JC spent 15+ years as a certified Master Mechanic before trading the shop for the keyboard. He's worked across dealerships, owned and operated his own independent garage, and consulted on automotive trade school curricula, reviewing technical textbooks used in vocational programs.
He now serves as Editor-in-Chief at emanuals.ai, where he oversees the platform's technical content. He's one of the few voices in automotive publishing who turned wrenches professionally for decades before he had a byline.
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