B5 S4 craks but does not start. No EPC light, No power to ECU pins 21 or 62

[pacs4]

Hi,
Long time MY2000 B5 S4 owner here. I need help! Parked my car, all seemed normal but the next day it would not start. Here's what I tried so far:

Turn the key and the car cranks promptly, so battery is good but the car does not start.

1. CEL and EPC light do NOT come on with other dash lights. (they should).
2. Typically this means bad ECU, but i sourced a replacement and get the same result.
2. Testing for power to the ECU, PIN 3 has power, but pins 21 and 62 do not.
3. VAG COM cannot find the ECU (As expected when pins 62 and 21 do not have power)
4. Pin 43 has power, VAG COM finds all K-line items except the ECU normally.
5. Disconnecting the battery for 24hours and trying again makes no difference.

I'm using this ECU diagram: http://nyet.org/cars/images/VAG_ME7.x.jpg


Questions:
What sends power to pins 21 and 62?
Should i be looking for a broken relay?

Thanks, pacS4

[illiGTI]

Hey dude- I am having the same problem! Do you have power at the ECu, fuel pump fuses?? Check out my post and let’s stay in touch!

[TheRussian]

Looking at the wiring diagram pin 62 goes toT10m/4 then to terminal 30
T10m/4-
Wire Connector, 10-point, black, connector station, electronics box in plenum chamber

Terminal (circuit) 30 -
Battery Positive voltage (B+), hot at all times

I looked for pin 21 off the ECU but I could not see that pin on there at all.

[illiGTI]

Where are you looking at the wiring diagram? Available online? This is helpful but without knowing the location of those wire connectors it’s hard to diagnose.

[Silverex]

https://drive.google.com/file/d/0B_z...pZTFBrM2s/view

[llama4yourmama]

B5s have problems with the ecm power supply relay. If youre not getting power at the ecm make sure you are getting power into the relay. Or just swap out the ecm power supply relay with a known good relay and try to start the car. Inspect the terminals to make sure they didn't get pushed out or corroded

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[pacs4]

B5s have problems with the ecm power supply relay. If youre not getting power at the ecm make sure you are getting power into the relay. Or just swap out the ecm power supply relay with a known good relay and try to start the car. Inspect the terminals to make sure they didn't get pushed out or corroded

Which relay is the ECM power relay? Everything i look at points me to an A4 diagram with relays in the ECU box inside the engine compartment. the S4 relays seem to be under the dash. Any help pointing me to the ECM power relay would be fantastic.

[Silverex]

Pretty sure the relays in the ecu box are the same ones under dash

[pacs4]

That sounds good.
I've attached photos of the relays under my 2000 Audi S4 dash & numbered each in yellow to make them easier to identify. You might need to click on the images to get a good view of them.
Can someone suggest which relay(s) might be responsible for ECM power?

B5 S4 2000 Relay photo 1.jpgB5 S4 2000 Relay photo 2.jpg

[Silverex]

I’d guess it’s either 7,4, or 8. The relays are kinda pricey new so I’d go to a junkyard and pull them or ask someone parting a car out

[llama4yourmama]

On the 1.8s the relay is in the engine compartment in the ecm box on the driver side cowl it should be the same on the 2.7s it's kind of a bitch to get the back two screws don't break the box or else it won't be water proof and you'll have even more problems later on

Which relay is the ECM power relay? Everything i look at points me to an A4 diagram with relays in the ECU box inside the engine compartment. the S4 relays seem to be under the dash. Any help pointing me to the ECM power relay would be fantastic.

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[llama4yourmama]

What codes do you have

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[pacs4]

>What codes do you have
The ECM does not have power, so no codes can be retrieved from it.

>On the 1.8s the relay is in the engine compartment in the ECM box on the driver side cowl it should be the same on the 2.7s
There are no relays in the MY2000 B5 S4 ECM box.
2000 B5 S4 ECM Box.jpg

The relays are under the dash.
Anyone know which relays power the ECM? if not any one know which relays do other things so i can remove them by process of elimination)? I've numbered them to make each easy to identify.

B5 S4 2000 Relay photo 1.jpg


B5 S4 2000 Relay photo 2.jpg

[pacs4]

In addition to the above, i have two fuse sockets not getting power (the fuses are fine).
#28 Fuel Pump
#29 Control Unit Engine

B5 S4 2000 Fuse Photo.jpg - 2000 B5 S4 Fuse Layout Pattern.jpg - 2000 B5 S4 Fuse Layout Sticker.jpg

[llama4yourmama]

The #3 relay is the fuel pump relay. So switch that with another relay with the same number and see if it starts up / gets power to the fuse

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[llama4yourmama]

You should still be able to read codes from the gateway or other control modules

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[TheRussian]

Where are you looking at the wiring diagram? Available online? This is helpful but without knowing the location of those wire connectors it’s hard to diagnose.

I got it off alldata. I have a subscription through them, worth the money for sure. But that pretty much all the info it gave. I can email you the diagram if you want. Pm me your email and I'll send you a link

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[zatch_303]

Anyone able to identify the ECU/ECM relay from the above pics?

[illiGTI]

Hey pacs4 hows it going on ur end? I'm hoping to do some more diagnosing this weekend on my issue.

[pacs4]

This module is not easily accessible. Anyone know a good way to get to the connectors? i can't get in there easily and don't want to damage anything.
Is it possible to get to this from the side? or do i need to remove these HVAC ducts? It seems the driver (left) side has metal all around. Any hints on how to proceed will be appreciated!

Module.jpg

[GrumpyBear]

I did this a few weeks ago. Those ducts pull out really easily - no fasteners; they just snap in. I think I only pulled off the one on the right. Then completely remove two mounting bolts, and loosen the back one, and you should be able to slide it out. There's a lot of slack in the cable.

Also I made sure to disconnect battery ground to prevent accidentally activating the airbag. I think I read somewhere to wait 15 min after disconnecting battery to make sure everything discharges.

[pacs4]

OK that sounds good. I looked and that seems feasible, except for one thing.
Does the plastic console surround here need to come off too? I tried removing the obvious screws (as shown by the arrow in the attached photo) but i do not have this off yet. Does it come off as one big piece that extends past the e-brake etc?

B5S4_plastic_console_surround.jpeg

[GrumpyBear]

OK that sounds good. I looked and that seems feasible, except for one thing.
Does the plastic console surround here need to come off too? I tried removing the obvious screws (as shown by the arrow in the attached photo) but i do not have this off yet. Does it come off as one big piece that extends past the e-brake etc?

I had taken both sides of the plastic console off. I'm not sure if I had to, but IIRC it was part of the instructions, and it started at the back end of the console (bolts under ashtray and armrest), and had to remove a cupholder, parking brake shroud, working forward until the cover you're asking about. There are two bolts somewhere near/behind the gear shift that also hold that piece in.

Do you have Bentley? The instructions there weren't completely accurate, but close enough that I was able to figure it out.

[pacs4]

Thanks GrumpyBear, with your help I was able to get the airbag control unit out today.

All, I reconnected the battery but car just cranks, no suggestion that it will start. I'll have to re-test the power to fuel and ECM to see if there are any changes with the air bag control out of the car.

[harryn]

Did you try starter fluid, just to see if it even tried to start or starts for a brief period then dies?

[pacs4]

Did you try starter fluid, just to see if it even tried to start or starts for a brief period then dies?

I did not do this, as the ECU/ECM is not responding. What would this tell me?

[harryn]

I did not do this, as the ECU/ECM is not responding. What would this tell me?

Fuses and relays ok? ECU fully connected with no bent pins? Do you have a spare ECU from a salvage yard you could use to see if wiring and electrical components are good?

[pacs4]

No bent pins. I have a spare ECU, it gives the same result. Fuses are OK.
#28 Fuel pump and #29 Control Unit Engine are not getting power, see post above for photos.

[Protection]

No bent pins. I have a spare ECU, it gives the same result. Fuses are OK.
#28 Fuel pump and #29 Control Unit Engine are not getting power, see post above for photos.

I spent about an hour looking over wiring diagrams, and the only thing I can find is that the ECU gets power through pin 62 via the Black connector T10m in the plenum pin 4. The power comes from “30” which is battery power. I could not find a fuse between the battery and ECU. Have you checked these two fuses (from your relay pic) to see if they are good? I couldn’t find any description in the wiring diagrams I have access to for those fuses. Honestly at this point I would be tempted to jump 12 to the back side of pin 4 on the black connector in the plenum and see if she starts.


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[Protection]

No bent pins. I have a spare ECU, it gives the same result. Fuses are OK.
#28 Fuel pump and #29 Control Unit Engine are not getting power, see post above for photos.

The one thing both those fuses have in common is that they are fed power through the fuel pump relay (the one marked “372”). Have you confirmed this relay is good? I suggest you remove the relay and jumper the load side (usually labels 30 from battery and 87 to item being fed power) and see if power is restored to those two fuses. If so, try and crank the car.

Also, are you sure that you have power on fuse # 34? That fuse is also fed power by fuel pump relay (J17). If you you do have power there, but none on #28 and #29 you have a broken/disconnect or corroded wire between the relay and the fuse panel.

Here is the wiring diagram for reference



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[pacs4]

@protection, Wow! this is really useful information. Yesterday I tested the #34 and while the fuses are good, I do not have 12v there. I'm going to go back through, re-test the fuse locations, relay, etc. I do have power at the two large fuses circled in your post from 9/8.

[Protection]

I did not think you would have power at Fuse #34 (S 234) if you did not have power at No. 28 and 29. From this we can conclude that your fuel pump relay (J17) is not switching on.

(I just deleted all the crap I wrote previously after re-reading this entire thread)

So I just re-read the entire thread and I am an idiot b/c I overlooked that you have no power at pin #62!

You will never have activation of the fuel pump relay if you don’t have power to the ECU. The ECU controls the relay by grounding it, but w/o power the ECU cannot do this.

Someone previously mentioned this, but power to the ECU comes via the black connector in the plenum. Before doing anything else, go under the hood, remove the ECU from the box and unplug the black connector in the plenum (see the pic below). Check to see if you have battery voltage on terminal #4 of the black connector in the plenum (not the part of the connector that is attached to the engine wiring harness part.). You should be seeing 12v here. Make sure the pin looks okay. If you don’t have 12v there is a break or poor contact in that wire. You will have to trace the wire back under the dash inside the car all the way to the power source. The wire is red per the diagram.

If you do have 12v here you will need to look at the terminal in engine side of the harness and check that wiring. Make sure the terminal is fully seated in the connector. For reference here is a picture (not mine) of the connector part for the engine harness. You can see the power feed wire is the fat red one. This runs to terminal # 62 on the ECU.








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[pacs4]

When I look in the ECU box, I don't have any connectors. if I look down the cowl, (is this the plenum?) mounted high in the foot well are 5 connectors.
The black connector does not have a thick red wire, only a thin one. Here are some photos.

Looking into the ECU Box, ECU in place:


Lifting up the ECU, there are no connectors in the box.


Moving aft, pulling back the wires, looking down:


Same set of connectors from the driver footwell:


A closer look from the top, the red wire gauge is smaller than expected on the black connector.


Looking at the adjacent connectors, 1, 2, 3...


Connectors 2, 3, 4....


Connectors 3, 4, - , 6



I have a MultiMeter and Test light now. I'll check for power on that black connector tomorrow even though the wire gauge is quite different.
is it possible that I should be looking at a different connector?

Thanks, all this help is awesome!

[pacs4]

Also to respond to the question about the Fuel Pump relay 372, I have a replacement relay. Swapping the relay makes no difference.

[Protection]

Yes, you are in the right location. (Nice clear photos BTW ) The best way to test that connector initially, is to insert a T-pin —or if you don’t have that a straight pin—into the backside of the connector that is visible to you so that the metal on the pin comes into contact with the metal terminal in position 4 (the solid red wire). The fact that your wire appears smaller is of no consequence, there are variations between years. Try not and disturb the connector too much during this check, b/c you may inadvertently “fix” the problem before you can find and fix it permanently.

With a pin in the backside of terminal #4/solid red wire (this is called “back probing”) you want to set your multimeter to volts DC and touch one lead to the pin and the other lead to a good ground or even the battery negative. You should see 12v. According to the wiring diagram this is a constant 12v so you shouldn’t have to turn the the key on. I anticipate that you won’t see any voltage. But for completeness, also turn the key on and check again.

Now that you’ve confirmed no voltage on the engine harness side of the connector it is okay to unplug the connector and inspect the terminals. You are looking for green corrosion on the terminals inside the both the male and female connectors. You also want to give a slight tug on the red wire and try and pull it from the connector. This is to make sure it is not corroded in the connector.

The next step if the examination above didn’t reveal anything, is to test for 12 v on the black connector unplugged. With the connector unplugged, you should be able to touch one end of your multimeter to terminal 4 in the black connector part that inside the car (not the half that is attached to the engine wiring harness) and see 12v. If you don’t have 12v you will have to trace that wire back under the dash to where it connects to the power distribution block under the dash—I may able to offer some insight later, but you should check that all the bolts marked 30 under the relay panel are snug.

In the event that when you back probed the terminal above in the first step you had 12v on your multimeter, your next test will be on the engine harness itself. You will need to unplug the ECU for this test. You will also need to set up your meter for an ohm/continuity test. You will have to swap the red lead (leaving the black lead in com) to the port with the ohm marking.

With the meter set up (I like to turn on the beep sound) touch the two leads together and confirm the meter beeps and shows continuity on the screen-it will display a number like 0.0005. Then touch one end to terminal 62 on the ECU connector harness and the other end to terminal #4 on the black connector you unplugged (the engine side of the harness). You should show continuity and hear a beep. If not you have a break in the engine harness that will have to be investigated.

If you have any questions post them or send me a DM/PM. I can give you my number so you can text or call. It may speed up this process.


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[pacs4]

I see good voltage on the black connector, for the two red wires in photos below.
I didn't work on the wiring harness test yet. I'll do that next.

[Protection]

Since you have 12v on that connector, before doing a continuity test, check terminal 62 on the ECU connector for 12v to confirm that the problem of no voltage on 62 is still present. If somehow voltage is restored to 62, plug the ECU in and try and start the car.


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[pacs4]

Now I feel good and bad.
I checked the continuity, and low and behold, BEEEEEEEP, it's there. Following up with a test shows I *do* have 12v power on ECU pin 62, but not 21.

I feel bad about asking for help searching out pin 62 info, but feel good that this is now confirmed to have 12v. I must not have tested it correctly before.
I guess this means means looking elsewhere. I disconnected the battery, plugged in the ECU, reconnected the battery and confirmed no Engine or EPC lights on the dash. I have two ECUs that do this. Other symptoms are the same. Car cranks well, but does not start.

Other ideas?

[pacs4]

I think I'm back to looking for something to send power to the ECU when the key is turned. Should I be looking for a relay? Maybe something with the ignition?

[Protection]

I have lots of ideas, haha. I think we are approaching this the wrong way. I was sidetracked by the discussion of power to the ECU and different pins. What we are dealing with is a “no comm”—no communication with the ECU.

Using VCDS, can you communicate with any other modules in the car? Specifically, can you communicate with the ABS module? If you are unable to communicate with any module, the most plausible scenario is that some component on the car is interfering with the can-bus network. This could be a component or sensor shorting out the network.

The way I have tested for this in the past (but not on a B5) is by the “unplug it” test. You will need to hook up your scan tool and one-by-one unplug modules until either comms are restored or you have unplugged everything. This is a bit of a pain b/c after unplugging a component you will then have to go back inside, turn the key on and try and communicate with the ECM. (I have a breakout box and a lab scope so I can look for the can hi and low signal without trying to communicate—saves time)

My first unplugged module would be the ABS unit. (Frequently a terminating resistor for the network is located there). Next would be the throttle body, etc...

But before you do that, can you go to the MAF sensor, roll back the rubber boot and back probe the purple/grey wire and see if you have 5v with the key on? See image below.




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