ECU schematics anywhere?

xubio

Active member
Joined
Feb 10, 2008
Location
Burnaby, BC
TDI
99 (A3) Jetta
Has anyone ever come across schematics for an ECU? (Particularly I'm interested in the ECU for my 99 Mk3 Jetta). My ECU won't respond at all to vag-com, and I think I have the problem narrowed down to the ECU.

Other than not being able to connect via vagcom, the ECU seems to work fine, so I'm hoping there's a simple connectivity problem on the board, and the schematic would help narrow my search further.

Brian
 

vwmikel

Vendor , w/Business number
Joined
May 5, 2005
Location
Las Vegas, NV
TDI
'94 Golf Sport TDI
Those schematics probably only exist in a Bosch building somewhere. I'm sure they are well guarded so I'd probably just give up on that one. Are you sure you don't just have a k-line problem? Aftermarket stereos frequently cause these problems.
 

xubio

Active member
Joined
Feb 10, 2008
Location
Burnaby, BC
TDI
99 (A3) Jetta
I don't have an aftermarket stereo. I checked the connection from the K line on the ECU (pin 61) to my obd connector (pin 7), all looked good. I also ruled out other devices affecting the K-line (such as a radio) by replacing the existing K-line wire on the obd connector and wiring it directly to the ECU. Still got a "no response from controller" message.

My bentley manual is incomplete in it's wiring diagram for the obd connector. I cannot find the K-line anywhere in the diagrams, and there's also another wire on pin 15 of the connector that I can't find. Anyone knows what this line is for?

Brian
 

vwmikel

Vendor , w/Business number
Joined
May 5, 2005
Location
Las Vegas, NV
TDI
'94 Golf Sport TDI
Are you sure it's not a problem with your vag-com cable? If you know that's fine then I'd probably just replace the ECU with a used one and be done with it.
 

Ben1000

Veteran Member
Joined
May 27, 2007
Location
Greensboro, NC
TDI
2001 Baltic Green 5spd
I don't see it mentioned, and I'm sure you've already checked; but what about fuses?

In the opendiag schematics the 12v on the OBD connector is used as part of the communications circuitry. Vag-com may also use the 12v? If so a blown fuse may be the culprit.

Go by a parts store that offers free OBD scans, if their scanner works then you know the communications are good and I would then be skeptical of the cable and/or software installation.
 

tongboy

Veteran Member
Joined
May 24, 2006
Location
Portland, OR
TDI
91 Jetta TDI Swap, 97 M3 LS1 Swap
make sure you have power to the appropriate wire on the ECU and just as importantly that the ground is there as well.

are you using a cheapo ebay knockoff cable? have you used the vag com recently with another known good car?
 

xubio

Active member
Joined
Feb 10, 2008
Location
Burnaby, BC
TDI
99 (A3) Jetta
Yes, I'm using a 3rd party cable (no flames, please ;)), *but*...

PB_NB was kind enough to let me try out my cable on his vehicle, and it works. We also tried his authentic ross-com cable on my car, and it also failed in the exact same manner as my 3rd party cable. So I'm pretty certain that my car is the problem.

Ben1000, thanks for the opendiag pointer, I'd not come across that before. Googling a bit more, I see that pin 15 is the "L line", and is sometimes used on older ECUs to wake up the ECU. I cannot find this wire in my Bentley, is this line used by Mk3 ECUs? Guess I'll have to trace this wire down to see where it goes...
 

Ben1000

Veteran Member
Joined
May 27, 2007
Location
Greensboro, NC
TDI
2001 Baltic Green 5spd
airwolftdi said:
When you turn your key on does the glowplug light turn on then go off? If not I would check your 109 relay.
If relay 109 was out it wouldn't be running though.

No shame in making your own hardware as long as the SW is legal.

Since it works on another car (mk4) and the connector is the same it should work on your mk3.



I'd check that there are 12V between 4 and 16 on your OBD port.

Also, you say you wired the k line directly from the ECU to the port; It would seem to me that this then leaves all of your other modules on the k line in the harness out of the loop, might want to consider reconnecting this to the harness.

The L line output on your cable is used to "wake up" the car modules, check that the output is working (probably is since it worked on another car)
 

tongboy

Veteran Member
Joined
May 24, 2006
Location
Portland, OR
TDI
91 Jetta TDI Swap, 97 M3 LS1 Swap
Ben1000 said:
Also, you say you wired the k line directly from the ECU to the port; It would seem to me that this then leaves all of your other modules on the k line in the harness out of the loop, might want to consider reconnecting this to the harness.

The L line output on your cable is used to "wake up" the car modules, check that the output is working (probably is since it worked on another car)
I've seen some bad modules blockade a K-line, hard ground or hard positive the line instead of leaving it open for other traffic - effectively blocking communication, going directly to the ECU resolves that possibility.

the chance that you have a running car (functionally running apparently) and no vag-com suggests that your ECU isn't dead, it's awfully hard to kill that specific portion of your ECU, usually now a days with electronics its all or nothing, you've gotta have a wiring issue somewhere getting to the ECU
 

Ben1000

Veteran Member
Joined
May 27, 2007
Location
Greensboro, NC
TDI
2001 Baltic Green 5spd
tongboy said:
..going directly to the ECU resolves that possibility.
For troubleshooting purposes, but once the problem is found it would make sence to put it back to the original harness. If you're going to go through the trouble then why not be able to see all modules?

Which brings up an interesting idea.... can you communicate to the other modules when you connect the k line in the harness (that now has the ECU disconnected) to the port? If so this would prove your cable works and that the ECU's output port is malfunctioning. Unlikely though, my guess is the port isn't getting power.
 
Last edited:

xubio

Active member
Joined
Feb 10, 2008
Location
Burnaby, BC
TDI
99 (A3) Jetta
With the ECU disconnected (K line only, L line still connected) I still cannot talk to any other controllers.

Pin 16 does indeed have 12V, and pin 4 (and 5) are both properly grounded.

Monitoring the K-line with my DVM while trying to establish a connection shows the voltage staying at 12V. I'd have expected the voltage to vary, but maybe my DVM is too slow. I'm gonna borrow a oscilloscope and have a closer look...
 

vwmikel

Vendor , w/Business number
Joined
May 5, 2005
Location
Las Vegas, NV
TDI
'94 Golf Sport TDI
They bring up a good point about communications with the other modules, that is a bit strange. You don't need the L line btw, I just use power, ground and K-line to run diagnostics and flash ECU's on the bench.
 

Ben1000

Veteran Member
Joined
May 27, 2007
Location
Greensboro, NC
TDI
2001 Baltic Green 5spd
Hate to be the one to say it, but It's gotta be the cable.

The odds of all modules losing their communications ports are very very low.

What kind of connectors are you using when cutting / reattaching the k line? It's not super high speed but it isn't DC either so this may be a factor.

I'd put everything on the connector back to stock and go somewhere for a free OBD scan ASAP as a sanity check.
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
Just curious, but what other modules can you talk to in an A3? My B4 has very limited options.
 

xubio

Active member
Joined
Feb 10, 2008
Location
Burnaby, BC
TDI
99 (A3) Jetta
Ben1000: I did that already, through the kindness of PB_NB. My cable worked on his vehicle, his ross-tech cable failed on my vehicle.
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
Thank you Ben. Airbag and engine for mine. Sounds about right.
 

Ben1000

Veteran Member
Joined
May 27, 2007
Location
Greensboro, NC
TDI
2001 Baltic Green 5spd
xubio said:
Ben1000: I did that already, through the kindness of PB_NB. My cable worked on his vehicle, his ross-tech cable failed on my vehicle.
Ahh I see, I didn't see anything about a "real" cable not working above.

I'm stumped then.. was it ever struck by lightning :confused:

Sounds like something really bad happened on the data bus suffcient to kill the output ports of all modules. Is there a chance when first building your cable that something could have shorted? (then fixed before testing PB_NB's car) Or did it go smoothly?
 
Last edited:

xubio

Active member
Joined
Feb 10, 2008
Location
Burnaby, BC
TDI
99 (A3) Jetta
I didn't build the cable, I bought it off of ebay for $20. I didn't do anything different with it on my car than on PB_NB's car, so I highly doubt the cable could have done any damage. I looked inside the cable, the K-line has a 500 ohm output resistor, which makes it quite unlikely that it could damage any other device on the bus.

I'm feeling rather stumped myself. Hopefully the oscilloscope tonight will tell me something.
 
Last edited:

xubio

Active member
Joined
Feb 10, 2008
Location
Burnaby, BC
TDI
99 (A3) Jetta
Yes, I have 12V on the K-line. In fact, I cannot seem to properly pull down the K-line. I tried pulling it low with a 1.5k Ohm resistor, which is close to the value used in the opendiag cable, and the voltage on the K-line doesn't budge from 12V. This is with the ECU disconnected from the K-line. I don't think I really care to figure this out, I'm only really interested in the ECU.

Unfortunately (or maybe fortunately;)), I managed to kill my cable while investigating with an oscilloscope (shorted a couple pins together when I opened up the cable to probe some signals inside). It's probably for the best, as now I don't have any good reason not to buy a real ross-tech cable and S/W.
 

rdkern

Top Post Dawg
Joined
May 21, 2004
Location
Humboldt Co CA
TDI
Passat 1997 silver (sold after 11 years), Jetta 2000 atlantic blue
The K line, with 12 volts, prevents the vagcom from getting a reading from the ecu. I'd disconnect the radio and try again. YOu say it's stock, but this is so similar to the aftermarket radio problem, I'd disconnect to see if it improves the situation.
 
Top