So for the past 7 or 8 months, the check-engine light on my wife's car has been turning itself on and off... Maybe 3 or 4 months ago it came on and stayed on... I used a basic scan-tool and reset the codes to clear the CEL, but it came right back after 10 or 15 minutes of driving...

So, anyway, this past weekend, it was time for an oil-change and a DSG transmission service, so I went ahead and did an auto-scan since I had my computer plugged into the car to measure the transmission-fluid temperature after the DSG service... It shows a "P0401 (001025) EGR Insufficient Flow -- Intermittent" code and a "P2002 (008194) Particulate Trap, Bank 1, Efficiency Below Threshold" code...

The car has had the VW TDI emissions fix done, about 70,000 to 80,000 miles ago, give or take a bit. I honestly don't remember exactly when we did it, but I know the car had less than 120K miles on it when we did that, and it has 190K miles right now... It's been at least 3 years... If it's really important, I can call the dealer at which we had it done and get the exact date and mileage...

Anyway, I'm hoping that fixing the EGR issue will fix the DPF code -- the DPF light is not on, only the check-engine light is on, and it doesn't seem to be doing any kind of extra regen or anything like that. My wife has noticed no issues with the car whatsoever -- no loss of power, no rough idle, nothing So it really doesn't seem as if the DPF is clogged...

I just need to know what to check in the EGR system to figure out what's going on there... I've never dealt with this issue before, and I'm hoping that y'all will be able to give me some step-by-step instructions to diagnose the issue and fix it. Thanks!

(I had just disconnected the battery for the transmission service, so you can ignore the stuff about the window-position error and the tire-pressure monitoring error in the auto-scan below -- those got fixed after.)

Here's the auto-scan:
Code:
Sunday,01,March,2020,16:31:12:64594
VCDS -- Windows Based VAG/VAS Emulator Running on Windows 10 x64
VCDS Version: 19.6.2.2 (x64)  HEX-V2 CB: 0.4508.4
Data version: 20200210 DS308.0
www.Ross-Tech.com


VIN: 3VWPL7AJ7CM648231   License Plate: 
Mileage: 305790km-190009mi   Repair Order: 



--------------------------------------------------------------------------------
--------------------------------------------------------------------------------


Chassis Type: AJ-VW36 (7N0)
Scan: 01 02 03 08 09 15 16 17 19 1C 25 2E 42 44 46 4F 52 56 62 72
          77

VIN: 3VWPL7AJ7CM648231   Mileage: 305790km-190009miles

01-Engine -- Status: Malfunction 0010
02-Auto Trans -- Status: OK 0000
03-ABS Brakes -- Status: Malfunction 0010
04-Steering Angle -- Status: OK 0000
08-Auto HVAC -- Status: OK 0000
09-Cent. Elect. -- Status: Malfunction 0010
15-Airbags -- Status: OK 0000
16-Steering wheel -- Status: OK 0000
17-Instruments -- Status: OK 0000
19-CAN Gateway -- Status: OK 0000
1C-Position Sensing -- Status: OK 0000
25-Immobilizer -- Status: OK 0000
2E-Media Player 3 -- Status: OK 0000
42-Door Elect, Driver -- Status: Malfunction 0010
44-Steering Assist -- Status: OK 0000
46-Central Conv. -- Status: OK 0000
4F-Centr. Electr. II -- Status: OK 0000
52-Door Elect, Pass. -- Status: Malfunction 0010
56-Radio -- Status: OK 0000
62-Door, Rear Left -- Status: OK 0000
72-Door, Rear Right -- Status: OK 0000
77-Telephone -- Status: OK 0000
-------------------------------------------------------------------------------
Address 01: Engine (CJA)       Labels: 03L-906-022-CBE.clb
   Part No SW: 03L 997 030 E    HW: 03L 907 309 AA
   Component: R4 2.0l TDI G000AG  9983  
   Revision: 12H14---    Serial number: 00000000000000
   Coding: 0050078
   Shop #: WSC 46741 001 1048576
   VCID: 303A195FC62C96A7795-8064

3 Faults Found:
008194 - Particulate Trap Bank 1 
               P2002 - 007 - Efficiency Below Threshold - MIL ON
             Freeze Frame:
                    Fault Status: 11100111
                    Fault Priority: 2
                    Fault Frequency: 1
                    Reset counter: 255
                    Mileage: 290725 km
                    Time Indication: 0
                    Date: 2014.02.20
                    Time: 07:42:49

             Freeze Frame:
                    RPM: 1702 /min
                    Speed: 53.0 km/h
                    (no units): 66.3
                    (no units): 30.6
                    (no units): 2.73
                    Pressure: 203 mbar
                    Pressure: 28 mbar

001025 - EGR System 
               P0401 - 001 - Insufficient Flow - Intermittent
             Freeze Frame:
                    Fault Status: 00100001
                    Fault Priority: 2
                    Fault Frequency: 191
                    Reset counter: 255
                    Mileage: 290754 km
                    Time Indication: 0
                    Date: 2014.02.20
                    Time: 16:38:17

             Freeze Frame:
                    RPM: 2438 /min
                    Speed: 53.0 km/h
                    Voltage: 13.30 V
                    Load: 81.6 %
                    Load: 100.0 %
                    Mass Air / Rev.: 325.0 mg/str
                    Mass Air / Rev.: 340.0 mg/str

001025 - EGR System 
               P0401 - 002 - Insufficient Flow - Intermittent
             Freeze Frame:
                    Fault Status: 00100010
                    Fault Priority: 2
                    Fault Frequency: 1
                    Reset counter: 255
                    Mileage: 305145 km
                    Time Indication: 0
                    Date: 2014.07.14
                    Time: 17:05:41

             Freeze Frame:
                    RPM: 2599 /min
                    Speed: 131.0 km/h
                    Voltage: 13.91 V
                    Load: 100.0 %
                    Load: 100.0 %
                    Mass Air / Rev.: 770.0 mg/str
                    Mass Air / Rev.: 760.0 mg/str

Readiness: 1 2 0 0 0 

-------------------------------------------------------------------------------
Address 02: Auto Trans        Labels: 02E-927-770.clb
   Part No SW: 02E 300 057 A    HW: 02E 927 770 AL
   Component: GSG DSG AG6     511 9334  
   Revision: 05351113    Serial number: 00001110011376
   Coding: 0000020
   Shop #: WSC 00066 000 00000
   VCID: 1768C2C34382619F18F-8042

No fault code found.

-------------------------------------------------------------------------------
Address 03: ABS Brakes (J104)       Labels:. 1K0-907-379-60EC1F.clb
   Part No SW: 1K0 907 379 BJ    HW: 1K0 907 379 BJ
   Component: ESP MK60EC1   H31 0121  
   Revision: 00H31001    
   Coding: 114B600C49260002880D06E7921A0042B70000
   Shop #: WSC 00066 000 00000
   VCID: 7BA0FE7353EAA5FF9C7-802E

1 Fault Found:
01325 - Control Module for Tire Pressure Monitoring (J502) 
            004 - No Signal/Communication - Intermittent
             Freeze Frame:
                    Fault Status: 00100100
                    Fault Priority: 2
                    Fault Frequency: 1
                    Reset counter: 131
                    Mileage: 305792 km
                    Time Indication: 0
                    Date: 2014.07.23
                    Time: 00:58:09

             Freeze Frame:
                    Count: 2
                    Count: 14
                    Count: 20480
                    Count: 16390
                    Count: 43008
                    Count: 0
                    Count: 258
                    Count: 0


-------------------------------------------------------------------------------
Address 08: Auto HVAC (J301)       Labels:| 3C8-907-336.clb
   Part No SW: 7N0 907 426 AN    HW: 7N0 907 426 AN
   Component: AC Manuell    H19 0404  
   Revision: 00001016    
   Coding: 0000001002
   Shop #: WSC 00066 000 00121
   ASAM Dataset: EV_ACManueBHBVW36X A01010
   ROD: EV_ACManueBHBVW36X_VW36.rod
   VCID: 005A899F3A8CC627C95-8054

No fault code found.

-------------------------------------------------------------------------------
Address 09: Cent. Elect. (J519)       Labels:. 1K0-937-08x-09.clb
   Part No SW: 5K0 937 084 G    HW: 5K0 937 084 G
   Component: BCM PQ35 B    011 2048  
   Revision: BG011001    
   Coding: 2F380E1F802F3EC4008800817000004441000086535D0560648020200040
   Shop #: WSC 46741 001 1048576
   VCID: 36362F472848B897239-8062

   Subsystem 1 - Part No: 5K1 955 119   Labels: 1KX-955-119.CLB
   Component: Wischer 15111  26  0512 
   Coding: 009795

1 Fault Found:
01504 - Bulb for License-Plate Light (X) 
            010 - Open or Short to Plus - Intermittent
             Freeze Frame:
                    Fault Status: 00101010
                    Fault Priority: 2
                    Fault Frequency: 42
                    Reset counter: 169
                    Mileage: 299904 km
                    Time Indication: 0
                    Date: 2014.05.18
                    Time: 16:26:36

             Freeze Frame:
                        Term 15 On
                    Voltage: 14.25 V
                        ON
                        ON
                        OFF
                        OFF
                        OFF


-------------------------------------------------------------------------------
Address 15: Airbags (J234)       Labels:| 5K0-959-655.clb
   Part No SW: 5K0 959 655 H    HW: 5K0 959 655 H
   Component: AirbagVW10G   013 0724  
   Serial number: 003GVRA0MPEJ  
   Coding: 00003133
   Shop #: WSC 00066 000 00000
   ASAM Dataset: EV_AirbaVW10SMEVW360 A01014
   ROD: EV_AirbaVW10SMEVW360.rod
   VCID: 3FD84A6307F279DFF0F-806A

   Seat occupied recognition: 
   Subsystem 1 - Part No SW: 1KM 959 339 B    HW: 1KM 959 339 B
   Component: BF-Gewichtss.  006 0001 
   Serial number: ---0000R--00002B7C00

   Crash sensor for side airbag: driver side: 
   Subsystem 2 - Part No SW: 1KM 955 557     HW: 1KM 955 557 
   Component: S.Sens.Fahr.V  H01 ---- 
   Serial number: 3572MSME5F161365ZZZZ

   Crash sensor for side airbag: front passenger side: 
   Subsystem 3 - Part No SW: 1KM 955 557     HW: 1KM 955 557 
   Component: S.Sens.Beif.V  H01 ---- 
   Serial number: 3582MSME4D151665ZZZZ

   Crash sensor for side airbag: rear: driver side: 
   Component: S.Sens.Fahr.H  --- ---- 
   Serial number: 3511HSME0E103029ZZZA

   Crash sensor for side airbag: rear: passenger side: 
   Component: S.Sens.Beif.H  --- ---- 
   Serial number: 3521HSME1A152F29ZZZR

   Crash sensor for front airbag: driver side: 
   Component: F.Sens.Fahr  --- ---- 
   Serial number: 35527SME03254028ZZZ0

   Crash sensor for front airbag: front passenger side: 
   Component: F.Sens.Beif  --- ---- 
   Serial number: 35627SME77094028ZZZE

No fault code found.

-------------------------------------------------------------------------------
Address 16: Steering wheel (J527)       Labels:| 5K0-953-569.clb
   Part No SW: 5K0 953 507 AH    HW: 5K0 953 549 B
   Component: Lenks.Modul   008 0080  
   Revision: --------    Serial number:  90440KIC000SX
   Coding: 188A140000
   Shop #: WSC 00066 000 00185
   ASAM Dataset: EV_SMLSNGKUDS A05001
   ROD: EV_SMLSNGKUDS_A05.rod
   VCID: 76B6EF476848F897E39-8022

   Multifunction steering wheel control module: 
   Subsystem 1 - Part No SW: 5K0 959 542 A    HW: 5K0 959 542 A  Labels: 3C8-959-537.CLB
   Component: E221__MFL-TAS  H09 0013 
   Serial number: 0691649             
   Coding: 820000

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments (J285)       Labels:| 5K0-920-xxx-17.clb-SRI1
   Part No SW: 5K0 920 972 C    HW: 5K0 920 972 C
   Component: KOMBI         H32 0310  
   Revision: X0032006    Serial number:               
   Coding: 270F01
   Shop #: WSC 00066 000 00121
   ASAM Dataset: EV_KombiUDSMM9RM10 A04305
   ROD: EV_KombiUDSMM9RM10_A04_VW36.rod
   VCID: 303A195FCAAC96A7795-8064

No fault code found.

-------------------------------------------------------------------------------
Address 19: CAN Gateway (J533)       Labels:. 7N0-907-530-V2.clb
   Part No SW: 7N0 907 530 K    HW: 1K0 907 951 
   Component: J533  Gateway H40 1620  
   Revision:   H40       Serial number: 20101101290042
   Coding: 352002
   Shop #: WSC 00066 000 00000
   VCID: 382A217F225C4EE7315-806C

No fault code found.

-------------------------------------------------------------------------------
Address 1C: Position Sensing        Labels: 1Kx-919-xxx-1C.lbl
   Part No SW: 5N0 919 879     HW: 5N0 919 879 
   Component: Kompass         001 0001  
   Revision: 00001000    Serial number: 1225223RF2VT06
   Coding: 0000002
   Shop #: WSC 00066 000 00000
   VCID: 7EA6F7674CF8B0D7BB9-802A

No fault code found.

-------------------------------------------------------------------------------
Address 25: Immobilizer (J334)       Labels:| 5K0-920-xxx-25.clb
   Part No SW: 5K0 953 234     HW: 5K0 920 972 C
   Component: IMMO          H32 0310  
   Revision: X0032006    Serial number:               
   Coding: 000000
   Shop #: WSC 00000 000 00000
   ASAM Dataset: EV_ImmoUDSMM9RM10 A01301
   ROD: EV_ImmoUDSMM9RM10_VW12.rod
   VCID: 6A8ECB372CF02C77771-803E

No fault code found.

-------------------------------------------------------------------------------
Address 2E: Media Player 3 (J650)       Labels:. 5N0-035-342.lbl
   Part No SW: 5N0 035 342 E    HW: 5N0 035 342 E
   Component: SG EXT.PLAYER H13 0240  
   Revision: A1001003    Serial number: 7660747997    
   Coding: 010000
   Shop #: WSC 00066 000 00000
   VCID: 290CF43BE9F6E76FBEB-807C

No fault code found.

-------------------------------------------------------------------------------
Address 42: Door Elect, Driver (J386)       Labels:| 3C0-959-70X-GEN4.clb
   Part No SW: 561 959 701     HW: 3C0 959 793 B
   Component: TUER-SG FT    002 0501  
   Revision: 13110009    Serial number: 0003599273
   Coding: 0004B5
   Shop #: WSC 01383 790 50316
   ASAM Dataset: EV_TSGFPQ35BRFVW46X A04001
   ROD: EV_TSGFPQ35BRFVW46X_VW36.rod
   VCID: 5BE09EF3F3AA45FFFC7-800E

   Slave Driver: 
   Subsystem 1 - Part No SW: 3C0 959 703 C    HW: 3C0 959 795 D  Labels: 1K0-959-70X-GEN4.CLB
   Component: J388__TSG-HL  007 1509 
   Serial number: 00000006141036      
   Coding: 000490

1 Fault Found:
66048 - Motor for Front Window Regulator 
          B11EC 54 [008] - Missing Calibration / Basic Setting
          Intermittent - Confirmed - Tested Since Memory Clear
             Freeze Frame:
                    Fault Status: 00000001
                    Fault Priority: 7
                    Fault Frequency: 1
                    Reset counter: 171


-------------------------------------------------------------------------------
Address 44: Steering Assist        Labels: 1K0-909-14x-GEN3.clb
   Part No: 1K0 909 144 M
   Component: EPS_ZFLS Kl. 70     3201  
   Revision: 00H20000    
   Shop #: WSC 02069 000 90108
   VCID: 3432154F3234AA871DD-8060

No fault code found.

-------------------------------------------------------------------------------
Address 4F: Centr. Electr. II (J520)       Labels:. 1K0-907-532.clb
   Part No SW: 7N0 907 532     HW: 1K0 907 951 
   Component: EZE_2         H40 1620  
   Revision:   H40       Serial number: 20101101290042
   Coding: 050B0500
   Shop #: WSC 00066 000 00000
   VCID: 6FB8DA231792C95F20F-803A

   Subsystem 1 - Part No SW: 8R0 959 591 A    HW: 8R0 959 591 
   Component: J245EE20SKB13  H02 0220 
   Serial number: 0123456789ABCDEFGHIJ

   Subsystem 2 - Part No SW: 8R0 959 591 A    HW: 8R0 959 591 
   Component: J394EE20SKB13  H02 0220 
   Serial number: 0123456789ABCDEFGHIJ

No fault code found.

-------------------------------------------------------------------------------
Address 52: Door Elect, Pass. (J387)       Labels:| 3C0-959-70X-GEN4.clb
   Part No SW: 561 959 702     HW: 3C0 959 792 B
   Component: TUER-SG BT    002 0501  
   Revision: 15110009    Serial number: 0003544102
   Coding: 0004B4
   Shop #: WSC 01383 790 50316
   ASAM Dataset: EV_TSGBPQ35BRFVW46X A04001
   ROD: EV_TSGBPQ35BRFVW46X_VW36.rod
   VCID: 5CE29DEFF6A442C7F5D-8008

   Slave Passenger: 
   Subsystem 1 - Part No SW: 3C0 959 704 C    HW: 3C0 959 794 D  Labels: 1K0-959-70X-GEN4.CLB
   Component: J389__TSG-HR  006 1509 
   Serial number: 00000005974099      
   Coding: 000490

1 Fault Found:
66048 - Motor for Front Window Regulator 
          B11EC 54 [008] - Missing Calibration / Basic Setting
          Intermittent - Confirmed - Tested Since Memory Clear
             Freeze Frame:
                    Fault Status: 00000001
                    Fault Priority: 7
                    Fault Frequency: 1
                    Reset counter: 171


-------------------------------------------------------------------------------
Address 56: Radio (J503)       Labels:. 5M0-035-1xx-56.clb
   Part No SW: 1K0 035 180 AE    HW: 1K0 035 180 AE
   Component: Radio Prem-8  H02 0016  
   Revision: -----16S    Serial number: VWZ4Z7L3221794
   Coding: 01000400040007
   Shop #: WSC 00066 000 00000
   VCID: 6390A613CB5A7D3FB47-8036

No fault code found.

-------------------------------------------------------------------------------
Address 77: Telephone (J412)       Labels:| 7P6-035-730.clb
   Part No SW: 5K0 035 730 E    HW: 5K0 035 730 E
   Component: TELEFON       H09 2902  
   Revision: 1B001001    Serial number: 00007660756438
   Coding: 0A10040000010100
   Shop #: WSC 01383 790 50316
   ASAM Dataset: EV_UHVNA A01719
   ROD: UHVNA.rod
   VCID: 2708F203FF62D11FA8F-8072

No fault code found.

End----------(Elapsed Time: 01:26, VBatt start/end: 12.2V/12.2V)-----------