B6 S4 crank but no start

B6/7 S4/RS4
#1

Hi, looking for help fixing my no start issue. I know that I have no fuel because the fuel pump relay is not functioning, but I can’t figure out why. I have used a multimeter to verify that I do have voltage coming to the relay where I should, but I’ve found that it is not receiving a ground from the ecu. I verified that there is continuity from that ground connection to the corresponding pin on the ecu connector. So I thought my problem was the ecu. I installed a used ecu and succesfully programed the immobilizer, but still have the same issue with the fuel pump relay. The new ecu gave me codes for both cooling fan circuits having a short to ground, but those were the only ones. I just cleared them out tonight and haven’t checked if they’ve come back yet but idk if that means anything.

my sai fuse is blown and the wires are bad, but I don’t believe that would cause any problems other than the sai fan not working as that fuse doesn’t control anything else. All of the relays uner the ecu, and the fuel pump relay, all tested ok and I even tried swapping them out with used ones. Despite the sai ground looking so bad, I’ve verified that the ecu ground which connects to the same place on the firewall is fine. I did a voltage drop test between pins 1 and 2 on the ecu connector (which are the main ground supply wires for the ecu) and the battery, and only got 13millivolts with the key on so I believe those are fine.

edit - just want to add that the crank sensor seems to be fine because I can see the rpm changing in vcds when I’m cranking. Apparently I have a bad clutch switch, because I noticed that it would sometimes crank without the clutch being depressed, but that’s not something that should cause this problem.

I’m a noob to electrical diagnostics and have been trying to learn as I go, but IDK where to go from here, can anyone offer any help finding out why my ecu won’t ground out the fuel pump relay?

#2

Welcome…

Lots going on here so lets start slow. Do you have a vag com? or what kind of code reader do you have?

#3

yes I’m using an official vag-com

#4

Ok do a full code scan and lets have you post the results here.

From there we can eliminate and the help icolate the best path for you. remember you can also do output tests on vag com. So when the time codes we can just do output tests and save you some time.

The wireharnes issues for the SAI are a big deal. I would strip back the wires and then see how far back all of that goes. Making sure to tape off the wires so they don’t continue to short out.

#5

ok here is what I got from a full scan:

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

Address 01: Engine Labels: 079-910-560-BBK.lbl
Part No SW: 8E0 910 560 Q HW: 8E0 907 560
Component: 4.2L V8/5V G 0010
Coding: 0007711
Shop #: WSC 03099 444 54104
VCID: 3365FE3E5172A81EDE-5124

No fault code found.
Readiness: 0110 1101

Address 03: ABS Brakes Labels: 8E0-614-517.lbl
Part No: 8E0 614 517 Q
Component: ABS/ESP allrad 3033
Coding: 04595
Shop #: WSC 06435
VCID: 3663C72A1200BD36F9-5124

1 Fault Found:
01826 - Sensor for Steering Angle (G85); Supply Voltage Terminal 30
35-00 - -

Address 08: Auto HVAC Labels: 8E0-820-043.lbl
Part No: 8E0 820 043 AD
Component: A4 Klimaautomat 1319
Coding: 00000
Shop #: WSC 63351
VCID: 63C54E7EF112789E6E-5140

1 Fault Found:
01206 - Signal for Duration of Ignition Off Time
27-00 - Implausible Signal

Address 09: Cent. Elect. Labels: 8E0-907-279-8E2.lbl
Part No: 8E0 907 279 F
Component: int. Lastmodul USA 0517
Coding: 01013
Shop #: WSC 63351
VCID: 3561C0260F06B62EF0-4B00

1 Fault Found:
01331 - Door Control Module; Driver Side (J386)
49-00 - No Communications

Address 15: Airbags Labels: 8E0-959-655-84.lbl
Part No: 8E0 959 655 C
Component: Airbag 8.4EP 3001
Coding: 0010707
Shop #: WSC 63351 000 00000
VCID: 377DCA2E450A443EE2-5140

1 Fault Found:
00532 - Supply Voltage B+
002 - Lower Limit Exceeded - Intermittent

Address 16: Steering wheel Labels: 8E0-953-549.lbl
Part No: 8E0 953 549 N
Component: Lenksáulenmodul 0611
Coding: 04041
Shop #: WSC 63351
VCID: 3E73DF0A3A30757621-4B00

3 Faults Found:
01303 - Telephone Transceiver (R36)
49-10 - No Communications - Intermittent
01301 - Control Module for Voice Recognition (J507)
49-10 - No Communications - Intermittent
01331 - Door Control Module; Driver Side (J386)
49-10 - No Communications - Intermittent

Address 17: Instruments Labels: 8E0-920-9xx-8E2.lbl
Part No: 8E0 920 980 M
Component: KOMBI+WEGFAHRS. RB4 D37
Coding: 03200
Shop #: WSC 22302
VCID: 3663C72A1200BD36F9-5140
WAUPL58E34A106488 AUZ6Z0C0268136

3 Faults Found:
00668 - Supply Voltage Terminal 30
53-10 - Supply Voltage Too Low - Intermittent
01314 - Engine Control Module
49-10 - No Communications - Intermittent
01331 - Door Control Module; Driver Side (J386)
49-10 - No Communications - 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 63351
VCID: 71E934363BEEDA0EEC-4B00

2 Faults Found:
00668 - Supply Voltage Terminal 30
07-10 - Signal too Low - Intermittent
01331 - Door Control Module; Driver Side (J386)
49-10 - No Communications - Intermittent

Address 46: Central Conv. Labels:. 8E0-959-433-MAX.clb
Part No: 8E0 959 433 BB
Component: Komfortgerát T7B 1411
Coding: 11852
Shop #: WSC 63351
VCID: 72EB3B3A3EE8E11615-4B00

Subsystem 1 - Part No: 8E1959801
Component: Tõrsteuer.FS BRM 0003

Subsystem 2 - Part No: 8E1959802E
Component: Tõrsteuer.BF BRM 0003

Subsystem 3 - Part No: 8E0959801A
Component: Tõrsteuer.HL BRM 0004

Subsystem 4 - Part No: 8E0959802A
Component: Tõrsteuer.HR BRM 0004

7 Faults Found:
01331 - Door Control Module; Driver Side (J386)
49-00 - No Communications
01134 - Alarm Horn (H12)
49-00 - No Communications
01369 - Alarm triggered by Hood Switch
35-00 - -
00955 - Key 1
35-00 - -
00532 - Supply Voltage B+
37-10 - Faulty - Intermittent
01331 - Door Control Module; Driver Side (J386)
80-00 - Single-Wire Operation
01561 - Rear left door
59-10 - Can’t Unlock - Intermittent

Address 55: Headlight Range Labels: 4Z7-907-357.lbl
Part No: 4Z7 907 357
Component: dynamische LWR D09
Coding: 00060
Shop #: WSC 63351
VCID: 04076DE2145CDFA637-4B1A

No fault code found.

Address 56: Radio Labels: 8E0-035-1xx-56.lbl
Part No: 8E0 035 195 H
Component: symphony II NP2 0400
Coding: 01225
Shop #: WSC 87808
VCID: 2C57E542DC4CF7E69F-5092

1 Fault Found:
01305 - Databus for Infotainment
37-10 - Faulty - Intermittent

Address 75: Telematics Labels: 8E0-035-616.lbl
Part No SW: 8E0 035 616 A HW: 8E0 035 616 A
Component: Telematik USA1
Coding: 0005303
Shop #: WSC 22302 444 54575
VCID: 23450E7EE192389E2E-5140

3 Faults Found:
01656 - Crash Signal
004 - No Signal/Communication - Intermittent
01531 - Emergency Battery
002 - Lower Limit Exceeded - MIL ON
01305 - Databus for Infotainment
014 - Defective - Intermittent

End-------------------------(Elapsed Time: 05:35)--------------------------

And then when I cleared those out and it immediately re-scanned, these were the ones that came back up again:

Address 01: Engine Labels: 079-910-560-BBK.lbl
Part No SW: 8E0 910 560 Q HW: 8E0 907 560
Component: 4.2L V8/5V G 0010
Coding: 0007711
Shop #: WSC 03099 444 54104
VCID: 3365FE3E5172A81EDE-5140

No fault code found.
Readiness: 0110 1101

Address 03: ABS Brakes Labels: 8E0-614-517.lbl
Part No: 8E0 614 517 Q
Component: ABS/ESP allrad 3033
Coding: 04595
Shop #: WSC 06435
VCID: 3663C72A1200BD36F9-5140

1 Fault Found:
01826 - Sensor for Steering Angle (G85); Supply Voltage Terminal 30
35-00 - -

Address 08: Auto HVAC Labels: 8E0-820-043.lbl
Part No: 8E0 820 043 AD
Component: A4 Klimaautomat 1319
Coding: 00000
Shop #: WSC 63351
VCID: 63C54E7EF112789E6E-5124

No fault code found.

Address 09: Cent. Elect. Labels: 8E0-907-279-8E2.lbl
Part No: 8E0 907 279 F
Component: int. Lastmodul USA 0517
Coding: 01013
Shop #: WSC 63351
VCID: 3561C0260F06B62EF0-4B00

No fault code found.

Address 15: Airbags Labels: 8E0-959-655-84.lbl
Part No: 8E0 959 655 C
Component: Airbag 8.4EP 3001
Coding: 0010707
Shop #: WSC 63351 000 00000
VCID: 377DCA2E450A443EE2-5140

No fault code found.

Address 16: Steering wheel Labels: 8E0-953-549.lbl
Part No: 8E0 953 549 N
Component: Lenksáulenmodul 0611
Coding: 04041
Shop #: WSC 63351
VCID: 3E73DF0A3A30757621-4B1A

No fault code found.

Address 17: Instruments Labels: 8E0-920-9xx-8E2.lbl
Part No: 8E0 920 980 M
Component: KOMBI+WEGFAHRS. RB4 D37
Coding: 03200
Shop #: WSC 22302
VCID: 3663C72A1200BD36F9-5124
WAUPL58E34A106488 AUZ6Z0C0268136

No fault code found.

Address 36: Seat Mem. Drvr Labels: 8E0-959-760.lbl
Part No: 8E0 959 760
Component: Sitzmemory R2 F 0305
Coding: 00002
Shop #: WSC 63351
VCID: 71E934363BEEDA0EEC-4AE8

No fault code found.

Address 46: Central Conv. Labels:. 8E0-959-433-MAX.clb
Part No: 8E0 959 433 BB
Component: Komfortgerát T7B 1411
Coding: 11852
Shop #: WSC 63351
VCID: 72EB3B3A3EE8E11615-4B00

Subsystem 1 - Part No: 8E1959801
Component: Tõrsteuer.FS BRM 0003

Subsystem 2 - Part No: 8E1959802E
Component: Tõrsteuer.BF BRM 0003

Subsystem 3 - Part No: 8E0959801A
Component: Tõrsteuer.HL BRM 0004

Subsystem 4 - Part No: 8E0959802A
Component: Tõrsteuer.HR BRM 0004

2 Faults Found:
01134 - Alarm Horn (H12)
49-00 - No Communications
01331 - Door Control Module; Driver Side (J386)
80-00 - Single-Wire Operation

Address 55: Headlight Range Labels: 4Z7-907-357.lbl
Part No: 4Z7 907 357
Component: dynamische LWR D09
Coding: 00060
Shop #: WSC 63351
VCID: 04076DE2145CDFA637-4B1A

No fault code found.

Address 56: Radio Labels: 8E0-035-1xx-56.lbl
Part No: 8E0 035 195 H
Component: symphony II NP2 0400
Coding: 01225
Shop #: WSC 87808
VCID: 2C57E542DC4CF7E69F-5092

No fault code found.

Address 75: Telematics Labels: 8E0-035-616.lbl
Part No SW: 8E0 035 616 A HW: 8E0 035 616 A
Component: Telematik USA1
Coding: 0005303
Shop #: WSC 22302 444 54575
VCID: 23450E7EE192389E2E-5124

1 Fault Found:
01531 - Emergency Battery
002 - Lower Limit Exceeded - MIL ON

End-------------------------(Elapsed Time: 05:51)--------------------------

#6

btw I’ve tried going into output tests when testing because I read that the ecu is supposed to keep the fuel pump running once you start the output tests. But the pump still doesn’t come on, and none of the things that are powered by the fuel pump relay will operate either (injectors, motor mounts, etc)

edit: although I was just now thinking and realized something - when I initially diagnosed the issue as the ecu not supplying ground, I was checking for ground without being in the output tests. I was expecting it to have ground at all times when KOEO but now I know that was a mistake. I guess maybe the ecu is providing ground but a wire supplying +12v to the fp relay is shorting out under load as soon as that happens. I’ll check again for ground from the ecu, but I’ll do it further back like either at the ecu connector or at the t17d connector, and I’ll do it with vcds in output tests.

#7

update - idk what I was doing wrong with my voltage drop testing last time, but I just did it again and I found that I have 12.4v of voltage drop on pin 65 of the ecu connector (which is the ground wire for the fuel pump relay) and I got 0.4v - 0.8v of drop on pins 1 and 2 (ecu main ground wires). so obviously I have a problem the ecu grounds.

edit - removed some info that I just realized I had all wrong… I think I need to figure out what the wiring diagram means when it says “earth connection 2 in front right wiring harness” because that’s where it says the ecu grounds go to. or is that going down the wrong path?

I’m planning to delete the sai system so I wasn’t too worried about the pump wires, but I guess I may need need to pull apart that wire loom and see if they damaged other wires in there as well…

#8

I would remove all of the damaged wires from the SAI broken wires in the harness. You can have wires aching out and then causing all sorts of issues. This has been an issue in the past where the SAI wires a bare and blow the fuseable link. but the signal wires can also get overloaded damaged etc.

The output test is a great tool. You can also provide a hot power lead to the pump just to make sure that the wires to the pump or the pump itself isn’t damaged and thus casuing an issue.

I would run a constant hot low voltage wire to the pump and verify at the rail that you’re getting fuel. Then attempt to start the car. That test if the car starts will tell you a lot. If you have fuel and you know it’s able to supply fuel and you still don’t get a start then you know the ECU and more of the grounding system need to be looked into

#9

updates - so I seem to have multiple issues going on. When I posted this thread I was definitely having a problem with the fuel pump relay not working. Right now, it seems like all of the electronics are fine and the only issue is that I’m not getting enough fuel delivery. I was questioning whether the electronics were ever an issue, because I don’t trust all of my initial diagnostic observations since I know I made a couple some noob mistakes at the beginning, but there’s no doubt that the fuel pump was not powered on when it should’ve been during at least one of my attempts to run output tests.

The only thing that changed when the electrical issue seemed to disappear, is that I jacked up the front end of the car. So I’m sure there must be a shorted wire or a bad ground somewhere and I still plan to open up that harness and find any issues it may have, but I’ve been trying to avoid that for as long as possible because I hate the thought of cutting into all the various layers of sheething in that harness. For now I just disconnected both of those sai wires on both ends to be sure they can’t have any current running through them, doesn’t seem like that made any difference though.

so when I realized that the relay was fully working but the car still wouldn’t start, I double checked my compression (I got ~148 on the lowest cylinder, 160 on the highest), and spark (only checked one coil so far though, just to make sure that the ecu is sending out the ignition pulse), and then I decided to try and replace the gas since the car has been sitting for a long time. I disconnected the fuel line at the fuel rail and put it into a gas can, and jumped the fuel pump at the fuse box. I measured >12 volts going to the pump at the fuse box, with only 0.25v of voltage drop on the positive side. It took more than 2 minutes to fill up a 1 gallon gas can, which seemed really slow, but when I do the math it’s actually pretty close to the expected 110 lph. There is an obvious problem with the pressure, though, because there is 0 pressure in the fuel line when I disconnect it from the rail. I don’t have an in-line pressure tester off hand to check the pressure while it’s running, but there is obviously no pressure at all in the line when I disconnect it even if I manually prime it first by jumping the fuse. I don’t even get any fuel spillage when I disconnect it. So I’m thinking the pressure regulator in the fuel filter is probably bad, if not the pump itself.

The pump and the filter both have fairly low miles on them, but the filter was making that puttering noise while priming (which many people say is an indication of a dying pump) ever since the pump and filter were both replaced with new oem parts a few years ago. Maybe one or both of them were defective from the beginning.

I think I will replace my filter next, and verify that I’m getting the full voltage at the pump itself to rule out any wiring issues between there and the fuse, and once I get that problem fixed I can go back to trying to tackle the intermittent electrical problem.

#10

Good update. A good fuel pressure gauge would be a good idea. I have seen brand new fuel filters being bad right out the box. Drove me crazy but that is worth looking into. So it looks like your on the right path.

#11

TY, so I installed a new fuel filter today and noticed no change. Then I loaned out a fuel pressure tester and hooked it up at the fuel rail, I got 0 psi while cranking, but if I jumped the fuse and waited for a few seconds it would build up to about 4 psi.

I don’t appear to be leaking fuel anywhere… some of the underbody panels near the filter do look suspiciously wet, but I’m guessing that’s just oil or something like that. Because if I was losing this much pressure through something like a cracked hose, I think it would have to be a really significant leak and I’d see liquid fuel somewhere which I don’t.

Is there any other potential cause I should be looking for now, besides a weak pump?

#12

I opened the tank and found a crack in the ribbed plastic line that connects from the actual pump, to the output port on the lid. I made it worse while I was trying to move the lid out of the way, but I assume it was already cracked and that’s where my pressure loss was going.

I assume I can just replace that with a rubber fuel hose? Maybe they used a plastic hose because it would be problematic to have a rubber one permanently subermged in fuel?

#13

Well sounds like you’ve found the issue. Plastic seems to stand up to fuel better that rubber that tends to breakdown when submerged in fuel according to an audi dealer tech I asked this same question to about 6 years ago. I don’t know how much of that I believe as you have rubber fuel lines where the fuel goes through the rubber there as well.

I would guess plastic fuel lines are just plain cheaper.