*UNIQUE*: ECU Short Resets ECU B7 S4

[q_dubz]

This is a fun one.

I've had a 2005.5 Audi S4 Manual 6spd for about 11 years. It has an electrical gremlin where it literally cuts out for a split second where the CEL and EPC light would pop on as well before disappearing. I've had it this problem for almost as long as I've owned the car but never could identify the source.

The difficulty in doing so lies in the fact that one, it would happen very sporadically, once every few months, weeks, days... and two, it would happen while cruising, part throttle tip-in, and/or at WOT. The biggest factor is that it would completely reset the ecu.
This was indicated by zero'd out fuel trims and any current DTCs being erased. Readily replicating the problem is nearly impossible but it is more susceptible at WOT/higher load than other conditions. Vehicle is now turbo but occurred even when NA.

Over the last year or two it's been getting WORSE. The ECU would even cut off at idle on a few occasions resulting in the engine shutting off of course. If I'm driving down the road, then it feels like a big misfire but since I'm in gear, the engine keeps going.

Diagnostic steps include:
Swapping ECU (went from B6 to B7 ECU, granted this was more so for ease/speed of flashing via NefMoto software)
Swapping ECU main power relay
Swapping Fuel Pump relay
Wire harness removal, inspection, and tone generator wire tracing (in progress as of last night 09DEC2024)

There is one code I've had pop up for many years and that is a low voltage code (terminal 30) which is strange because that's constant 12v. I never found any issues.

Earlier this year when one of the resets occurred, the ECU finally stored five codes:

Short to grounds:

Inj 1, 4, 8
Evap Solenoid (N80)
Internal RAM error

Wiring diagrams show shared 12v amongst those components however, that's switched 12v (terminal 15) things. I'm not certain that would cause a hard ECU reset like what disconnecting the battery would do, but I could be wrong so here at wit's end looking for experts.

Note: This ECU does not give freeze frame data which also sucks.

Chassis Type: 8E (8E - Audi A4/S4/RS4 B6/B7 (2001 > 2008))
Scan: 01 02 03 08 09 0F 11 15 16 17 18 25 36 37 45 46 55 56 57 65
          67 69 75 76 77
 
VIN: WAUZZZ8E14A070783   Mileage: 189190km-117557miles
-------------------------------------------------------------------------------
Address 01: Engine        Labels: 079-910-560-BBK.lbl
   Part No SW: 8E0 910 560 G    HW: 8E0 907 560
   Component: 4.2L V8/5V      G   0040
   Revision: 00000000    Serial number: AUZ6Z0C0242432
   Coding: 0011711
   Shop #: WSC 87119 806 641192
   VCID: 295922AA83FAA1C5F5-5124
   VINID: 9D196AAAA2150444401C01C80C63F280E1

16666 Fuel Injector #8 (N86) 
                P0282 002 Short to Ground Intermittent 
17833 EVAP Purge Valve (N80) 
                P1425 002 Short to Ground Intermittent 
16645 Fuel Injector #1 (N30) 
                P0261 002 Short to Ground Intermittent 
16654 Fuel Injector #4 (N33) 
                P0270 002 Short to Ground Intermittent 
16988 Internal Control Module 
                P0604 008 RAM Error
Readiness: 0110 0100

-------------------------------------------------------------------------------
Address 03: ABS Brakes        Labels: 8E0-910-517.clb
   Part No SW: 8E0 910 517 C    HW: 8E0 614 517 BB
   Component: ESP8 quattro    H04 0180
   Revision: 00000000    Serial number: 00000000000000
   Coding: 0004901
   Shop #: WSC 06335 000 00000
   VCID: 275D249296EE97B5E3-8072

1 Fault Found:
01826 - Sensor for Steering Angle (G85); Supply Voltage Terminal 30
            000 - -

-------------------------------------------------------------------------------
Address 08: Auto HVAC        Labels: 8E0-820-043.lbl
   Part No: 8E0 820 043 AM
   Component:   A4 Klimaautomat   2731
   Coding: 00000
   Shop #: WSC 00000
   VCID: 6CD71BBE1C8874ED4E-5124

1 Fault Found:
00819 - High Pressure Sensor (G65)
            07-00 - Signal too Low

-------------------------------------------------------------------------------
Address 09: Cent. Elect.        Labels: 8E0-907-279-8EC.lbl
   Part No: 8E0 907 279 J
   Component: int. Lastmodul  USA 0503
   Coding: 01023
   Shop #: WSC 65536
   VCID: 3979F2EA235A114585-4B00

4 Faults Found:
01496 - Bulb for Fog-Lamps; Left (L22)
            30-00 - Open or Short to Plus
01500 - Bulb for Fog-Lamps; Right (L23)
            30-00 - Open or Short to Plus
01518 - Bulb for Back-Up Lights; Left (M16)
            30-00 - Open or Short to Plus
01519 - Bulb for Back-Up Lights; Right (M17)
            30-00 - Open or Short to Plus

-------------------------------------------------------------------------------
Address 0F: Digital Radio        Labels: 8E0-035-593-XM.lbl
   Part No SW: 8E0 035 593 E    HW:            
   Component: SDAR XM            
   Revision:             Serial number: AUZ4Z7D3021736
   Shop #: WSC 00000 000 00000
   VCID: 2B55D8A28906B3D507-515E

1 Fault Found:
02635 - Tuner Not Enabled/Activated
            000 - -

-------------------------------------------------------------------------------
Address 15: Airbags        Labels: 8E0-959-655-94.lbl
   Part No SW: 8E0 959 655 H    HW: 8E0 959 655 H
   Component:    Airbag 9.41  H10 3230
   Revision: 91H10323    Serial number: 0036N000CWJ9
   Coding: 0032707
   Shop #: WSC 06335 000 00000
   VCID: 3C77EBFE7F68246D9E-8068

   Subsystem 1 - Part No: 8E0 910 339 B
   Component: BF-Gewichtsens. 02  0070
   Serial number: 6332DRB401818618G
   Coding: 00032707

   Subsystem 2 - Serial number: 6342DRB401829425F

   Subsystem 3 - Serial number: 6352ARB4003B259CO

   Subsystem 4 - Serial number: 6362ARB4003B62308

   Subsystem 5 - Serial number: 63729RB4005238089

   Subsystem 6 - Serial number: 63829RB400523AC9P

1 Fault Found:
01316 - ABS Control Module
            004 - No Signal/Communication - Intermittent

-------------------------------------------------------------------------------
Address 16: Steering wheel        Labels: 8E0-953-549.lbl
   Part No: 8E0 953 549 Q
   Component: Lenksáulenmodul     0601
   Coding: 01041
   Shop #: WSC 06335
   VCID: 41899A0A4B8A4985CD-4B00

No fault code found.

-------------------------------------------------------------------------------
Address 17: Instruments        Labels: 8E0-920-9xx-8EC.clb
   Part No SW: 8E0 920 981 Q    HW: 8E0 920 981 Q
   Component: KOMBI+WFS 4     H12 0040
   Revision: 0040        Serial number: 00000000000000
   Coding: 0023204
   Shop #: WSC 02301 444 10073
   VCID: 3B75E8E27966235597-5124

1 Fault Found:
01304 - Radio
            004 - No Signal/Communication - Intermittent

-------------------------------------------------------------------------------
Address 25: Immobilizer        Labels: 8E0-920-9xx-8EC.clb
   Part No SW: 8E0 920 981 Q    HW: 8E0 920 981 Q
   Component: KOMBI+WFS 4     H12 0040
   Revision: 0040        Serial number: 00000000000000
   Coding: 0023204
   Shop #: WSC 02301 444 10073
   VCID: 3B75E8E27966235597-5124

1 Fault Found:
01304 - Radio
            004 - No Signal/Communication - Intermittent

-------------------------------------------------------------------------------
Address 36: Seat Mem. Drvr        Labels: 8E0-959-760.lbl
   Part No: 8E0 959 760
   Component: Sitzmemory R2 F     0305
   Coding: 00002
   Shop #: WSC 00000
   VCID: 71E90ACA3BAA99057D-4ACE

1 Fault Found:
00668 - Supply Voltage Terminal 30
            07-10 - Signal too Low - Intermittent

-------------------------------------------------------------------------------
Address 37: Navigation        Labels: 8E0-035-192-RNSE.clb
   Part No SW: 8E0 035 192 E    HW: 8E0 035 192 E
   Component: RNS-E US        H54 0260
   Revision:      03S    Serial number: AUZBZ7E1501313
   Coding: 0309167
   Shop #: WSC 06335 000 00000
   VCID: 2643299692E48EBDD8-515E

3 Faults Found:
00858 - Connection; Radio Intermediate Frequency (IF) Output to Antenna Amplifier
            011 - Open Circuit - Intermittent
00466 - Control Module for Steering Column Electronics (J527)
            008 - Implausible Signal
01044 - Control Module Incorrectly Coded
            000 - -

-------------------------------------------------------------------------------
Address 46: Central Conv.        Labels:. 8E0-959-433-MAX.clb
   Part No: 8E0 959 433 BT
   Component: Komfortgerát T7B    3232
   Coding: 11902
   Shop #: WSC 06335
   VCID: 0407531E14189CADA6-4AE8

   Subsystem 1 - Part No: 8E1959801F
   Component: Tõrsteuer.FS BRM 1315

   Subsystem 2 - Part No: 8E1959802E
   Component: Tõrsteuer.BF BRM 0205

   Subsystem 3 - Part No: 8E0959801A
   Component: Tõrsteuer.HL BRM 0205

   Subsystem 4 - Part No: 8E0959802A
   Component: Tõrsteuer.HR BRM 0205

2 Faults Found:
01134 - Alarm Horn (H12)
            29-00 - Short to Ground
00955 - Key 1
            35-00 - -

-------------------------------------------------------------------------------
Address 55: Headlight Range        Labels: 4F0-910-357.lbl
   Part No SW: 4F0 910 357 E    HW: 4F0 907 357 E
   Component: AFS 1           H01 0010
   Revision: 00000001    Serial number:              
   Coding: 0000019
   Shop #: WSC 01041 444 52566
   VCID: 285F27AE9BF098CDEA-807C

   Subsystem 1 - Part No: 8E0 941 329 A
   Component: AFS-Modul links H05 0030

   Subsystem 2 - Part No: 8E0 941 329 A
   Component: AFS-Modul rechtsH05 0030

1 Fault Found:
01314 - Engine Control Module
            004 - No Signal/Communication - Intermittent

-------------------------------------------------------------------------------
Address 56: Radio        Labels: 8E0-035-192-RNSE.clb
   Part No SW: 8E0 035 192 E    HW: 8E0 035 192 E
   Component: RNS-E US        H54 0260
   Revision:      03S    Serial number: AUZBZ7E1501313
   Coding: 0309167
   Shop #: WSC 06335 000 00000
   VCID: 2643299692E48EBDD8-515E

3 Faults Found:
00858 - Connection; Radio Intermediate Frequency (IF) Output to Antenna Amplifier
            011 - Open Circuit - Intermittent
00466 - Control Module for Steering Column Electronics (J527)
            008 - Implausible Signal
01044 - Control Module Incorrectly Coded
            000 - -

End-------------------------(Elapsed Time: 06:36)--------------------------

 

[scoper]

Drag test the ECU plug power terminals.

If it's not that you are going to need a scope, a few thousandths of a second of power/gnd drop out will be enough to cause the issue.
Does not need to be fancy as you are only looking for a drop out at a particular point - you may even be able to see partial drops that would otherwise go un-noticed.
Look on ebay/amazon for a FNIRSI-DSO 152, tiny thing but powerful enough for this job and about $40- I have one for when the Pico is not needed. Extend the leads so you can have it in the car where you can see it, set it to 500ms/division that will give you 5s on the screen - plenty to glance at the screen when it faults.
Then it is a bit of trial and error. connect the ground side securely to the battery and back probe at the ECU into one of it's power supplies (T30/15)- drive until it faults and see if the scope shows the drop out (or spike in the case of the grounds), rinse and repeat with all the power's and grounds on the ECU until you see the spike - then you know which wire it is on. I would start with a T30 supply from the code you said sets.
Then go halfway upstream on that wire (component wise) to the battery and re-test, keep halving until you narrow it down.

 

[q_dubz]

Yea, I was looking at small form-factor O-scopes last night at the behest of others. Thanks for the guidance! I'm fairly certain that is the way I'm going to do. Besides that, i guess i could perform jumpers for the few 12v and GNDs the ecu has. I'll dig back into the wiring diagrams tonight and ID them all. I'm just hoping nothing is below the dash but most likely is for ECU supply... ugh.

 

[q_dubz]

autoscan with codes added posted.

 

[Uwe]

autoscan with codes added posted.

The four "Short to Ground Intermittent" faults might point to a missing +12V on the other side of those actuators. They get switched ON when the ECU pulls its side to ground ("low side switching").

However, the "Internal Control Module RAM Error" fault makes me wonder about the ECU itself, and if the ECU is being flaky, then I could see it setting spurious fault codes...

-Uwe-

 

[q_dubz]

The four "Short to Ground Intermittent" faults might point to a missing +12V on the other side of those actuators. They get switched ON when the ECU pulls its side to ground ("low side switching").

However, the "Internal Control Module RAM Error" fault makes me wonder about the ECU itself, and if the ECU is being flaky, then I could see it setting spurious fault codes...

-Uwe-

Yes, i know it's referring to 12v+ and also how the ECU operates pulling to ground. This 12v+ is shared amongst 12 other components, mostly solenoids, then the o2s, and the MAF. The MAF could explain the EPC light illuminating during the event.

All 12 of these components pull from one fuse which is fed by the FP relay. The injectors however are divorced, still fed by the FP relay but with their own dedicated fuse and wire.

The RAM error could very well just be a result of a sudden loss of power in the middle of a calculation/unexpected shutdown and restart. Most computers don't like that kinda thing

Since this is the FIRST time in 11years of experiencing this problem that any code persisted after the event, i can't rule that as a root cause, especially since this is ECU #2 and the same thing is occurring.

A short on this side of things, external to the ECU should NOT be causing the ECU to do a full reset. The ECU shutting down would cut's the FP relay signal (pin #65) and subsequently I'm getting these kinds of codes to external components.

So what i will do first is the cheap route, create a fused 12v jumper to the ECU's primary power, go for a test drive and see if I can replicate it. There's only two other 12v pins, tiny ones, #62 and #21.

 

[q_dubz]

So dug into the diagram to understand the flow of electrons...

ECU Pin 121/62 is basically the "always-on" pin. There isn't even a fuse shown before it (strange).

62 receives 12v from battery via 6mm wire feeder (which also splits to SAI fuse and to the ECM Relay).
ECM Relay is GND'd via ECU pin 23
ECM Relay powers Cam Solenoids, fan control modules and Coolant Aft. Pump

The ECM relay feeds the ECU via 2.5mm wire ECU Pin #3

---

ECU Pin 121/21 is basically the "wake-up" pin. The IGN SW sends power here and to the FP relay, then pin 23 grounds the signal to the ECM relay, which activates and the ECU turns on fully.

---

So, since 62 is always-on, that would be the one responsible for maintaining ECU memory. If the wiring prior to pin 62 had a short, the ECM relay would trip as well resetting the ECU.

This doesn't explain the blip of the CEL and EPC lights or the components on the other side of the FP relay giving short to ground codes but could just be a function of the ECU dying.

For one it gives me somewhere to start digging.

That's enough brain work for tonight.

 

[q_dubz]

hello everybody!

update on this: so I ran the ECU power straight to battery and drove it around for a couple weeks and the ECU stopped cutting out however I did see the cluster blink both flasher lights at me a few times which was something that would occur on occasion when this short happened so the fault is somewhere behind the dash.

but it's nice to finally not have power cutouts to the engine while driving!

 

[EuroX]

I would start with RAM error. Different ECU to start.

 

[q_dubz]

I would start with RAM error. Different ECU to start.

you missed the part where i said i swapped ECUs.

 

[EuroX]

you missed the part where i said i swapped ECUs.

I didn't miss it. Either post an updated log that doesn't have a ram error code stored or make sure you have a good working ecm first. According to your log:

Address 01: Engine Labels: 079-910-560-BBK.lbl
Part No SW: 8E0 910 560 G HW: 8E0 907 560
Component: 4.2L V8/5V G 0040
Revision: 00000000 Serial number: AUZ6Z0C0242432
Coding: 0011711
Shop #: WSC 87119 806 641192
VCID: 295922AA83FAA1C5F5-5124
VINID: 9D196AAAA2150444401C01C80C63F280E1

16666 Fuel Injector #8 (N86)
P0282 002 Short to Ground Intermittent
17833 EVAP Purge Valve (N80)
P1425 002 Short to Ground Intermittent
16645 Fuel Injector #1 (N30)
P0261 002 Short to Ground Intermittent
16654 Fuel Injector #4 (N33)
P0270 002 Short to Ground Intermittent
16988 Internal Control Module
P0604 008 RAM Error
Readiness: 0110 0100

Also if you feel it's no an ecm issue please provide evidence to rationalize this conclusion.

 

[q_dubz]

I didn't miss it. Either post an updated log that doesn't have a ram error code stored or make sure you have a good working ecm first. According to your log:



Also if you feel it's no an ecm issue please provide evidence to rationalize this conclusion.

Please re-read entire thread and digest it. Especially post #8.

 

[EuroX]

Please re-read entire thread and digest it. Especially post #8.

Please re-read entire post #11 and post update auto scan that does not show ram error code if thats the case.

 

[q_dubz]

Please re-read entire post #11 and post update auto scan that does not show ram error code if thats the case.

i don't need to waste my time hooking up the laptop to repost a scan just to show the code is gone when I can just tell you the code is gone. Serves no benefit when the source of the problem has already been determined.

 

[Uwe]

so I ran the ECU power straight to battery and drove it around for a couple weeks and the ECU stopped cutting out

Serves no benefit when the source of the problem has already been determined.

I suppose it is possible that a very brief power interruption could cause the ECU to set a RAM Error fault.

Sounds like you need to figure out where the dodgy connection is. Good luck.

-Uwe-

 

[EuroX]

i don't need to waste my time hooking up the laptop to repost a scan just to show the code is gone when I can just tell you the code is gone. Serves no benefit when the source of the problem has already been determined.

Sounds like you got it figured out.