BRM Runs for Few Seconds - CAN Bus Not Ready

Quick Synopsis: 2006 Jetta BRM 5 speed

Ran great then started cutting out then wouldn't start the next day.
Replaced: Cam sensor, crank sensor, lift pump and dual pump on side of head, battery (freshly charged)

Car now starts and runs for a few seconds then shuts off due to the immobilizer after 2 seconds, CAN bus is down but K1 and K2 are good.

Traced engine bay wiring from front of block to firewall and ECU. No broken wires. A few lightly chafed up by the cooling fans and found a few chewed on up in the rain gutter but not all the way through (mouse nest right on top of the harness) and none of them were twisted pair bus wires.

Cleaned all grounds that I can locate in the engine bay.
Cleaned all the positive leads and fuses on the front of the engine bay fuse box (quite a bit of corrosion aka rust on these).

Still no dice.

Can someone post the wiring diagrams for the two harnesses that plug into the ECU so I can see which wires were chewed on and I'd like to check power to the ECU and also pin check the bus lines connected to the ECU.

Any other methods of sniffing out the wiring culprit or how to tell if the CAN bus module or ECU is bad would be helpful too.

If the immobilizer is triggered, it'll only start for a little and then die. I'd chase that down first. Perhaps you have a problem with the immobilizer, or with the key or something like that. Do you have vag-com?
I see you're in Missouri, where at?

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I'm near the KC area and I do have VCDS, thanks.
That's how I found the issues I have so far...no way to live without VCDS on these things.
What I didn't post is a few things I've found in research (didn't want to get too long winded)
1. When the CAN Bus is down and the cluster and ECU can't talk then the immobilizer will activate keeping the car from running.
2. Most of these little gremlins is due to a bad battery, dirty grounds, dirty power feeds to the ECU or broken/chafed wires.
3. I have tons of lights and error codes and issues due to what I believe is the CAN Bus being down. No glow plug light, steering light comes on, cooling fans turn on full speed when I turn the key on, no wipers, no blinkers, no flashers, no dash lighting with lights on, immobilizer light comes on for about 2 secs then goes out, if I leave the ignition on I get a flashing red brake warning with warning beeps.

I would check the grounds INSIDE the car, as well as the connections at the Central Electronics box near the pedal area, and possibly the connection for the Load Reduction relay in the CE box, as well as connections at the Instruments.

Sounds like you have a problem somewhere in the dash. I don't think the ECU in the cowl cares about the immobiliser beyond what it is told from inside the car.

Are there any other DTCs in any other modules? Specifically the CAN Gateway?

Thanks for the pointers!!
I'll pull the gauge cluster and look back there as well as pull the central electronics box and see how all the connectors look. Though I'm not sure which relay on the CE box is the load reduction relay (more familiar with the mk4)

oilhammer said:

Are there any other DTCs in any other modules? Specifically the CAN Gateway?

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All the codes I got in my auto scan were:
P0568, p1650, p1699, p1637, p1635, p1570, p161a, p161d.

I tried to get into module 19 to look at the Gateway but it errored out, should have guessed when I initially checked and saw the CAN bus wasn't ready.

The CAN Gateway is a little box on a clip above the accelerator pedal. Might check its connector, too.

The part number should be 7N0-907-530-H, black plastic box, one connector, has Continental on it. I wonder if yours is dead somehow. All the CAN bus stuff goes through that Gateway.

I haven't ever had to mess with can on the VW cars, but I've done some on hd trucks. One of the common things which takes can down is a shorted intelligent device (sensor, module, etc.) At the obd connector pins 6 and 14 should be can high and low. If you check voltage between them, it should be koeo +-2 volts. If you check the ohms between them, it should be 60ohms. They should have no continuity to ground or to battery positive.

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oilhammer said:

The part number should be 7N0-907-530-H, black plastic box, one connector, has Continental on it.

Click to expand...

The connector and wiring looks solid but mine is 1K0-907-530-H and says Temic
Checked the CE and everything looks good and pulled the connectors and all but the 460 relays and gave a quick look at the wires. Also checked the grounds down by the kick panels on each side. The cluster wiring and connector looks good too.

Mozambiquer said:

At the obd connector pins 6 and 14 should be can high and low. If you check voltage between them, it should be koeo +-2 volts. If you check the ohms between them, it should be 60ohms. They should have no continuity to ground or to battery positive.

Click to expand...

I'll have to give this a try after I put some of the stuff back together. I figured if I had a broken bus wire that'd give me the same symptoms and just haven't found any signs yet.

What are the purpose of the following wires that go to the large connector on the ECU? They were chewed on and I wonder if they shorted.

-Black with white stripe
-Black with light blue stripe
-Light blue with dark blue stripe

Well, got a Bentley manual on the way. Gotta do some pin checks and maybe see if the signals / power / grounds into the Gateway module are all working right.

Reading it sounds like a gateway module failure is rare, though they're cheap for a used one, figure I can do a few more checks before I try a replacement.

ihredneck said:

Well, got a Bentley manual on the way. Gotta do some pin checks and maybe see if the signals / power / grounds into the Gateway module are all working right.

Reading it sounds like a gateway module failure is rare, though they're cheap for a used one, figure I can do a few more checks before I try a replacement.

Click to expand...

If you find out the gateway module is bad, I've got one on my parts car. I'd send it for a good deal.

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CAN Gateway failure would be rare, I agree. But perhaps a wire or connector to it.

You can communicate with the Gateway OK? Does it have any DTCs?

oilhammer said:

CAN Gateway failure would be rare, I agree. But perhaps a wire or connector to it.
You can communicate with the Gateway OK? Does it have any DTCs?

Click to expand...

When I test, CAN is "Not Ready" or down so I have no communication.
Unless there is a backdoor via VCDS I haven't been able to open the module for it because it is "Not Ready"

Mozambiquer said:

If you find out the gateway module is bad, I've got one on my parts car. I'd send it for a good deal.

Click to expand...

thanks!

Mozambiquer said:

I haven't ever had to mess with can on the VW cars, but I've done some on hd trucks. One of the common things which takes can down is a shorted intelligent device (sensor, module, etc.) At the obd connector pins 6 and 14 should be can high and low. If you check voltage between them, it should be koeo +-2 volts. If you check the ohms between them, it should be 60ohms. They should have no continuity to ground or to battery positive.

Click to expand...

I tested across pins 6 & 14 on the OBD II connector.
- 67 ohms across pins
- 0V between pins
- no continuity to battery positive
- wasn't getting a positive continuity sound test to battery ground, but resistance fluctuated from 80 ohms to 200 ohms

ihredneck said:

I tested across pins 6 & 14 on the OBD II connector.
- 67 ohms across pins
- 0V between pins
- no continuity to battery positive
- wasn't getting a positive continuity sound test to battery ground, but resistance fluctuated from 80 ohms to 200 ohms

Click to expand...

Was that with the gateway plugged in and key on? You should have no continuity to ground, which would mean you have a short to ground somewhere. Most often that would be in a module, but can also be a can wire rubbed through in the harness. Let me look at the can-bus wiring diagram for that car and there would be several checks you can do.
Was pin 6 or 14 higher ohms to ground?

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Orange and black will be can-bus high, orange and brown is can-bus low. They go from the datalink connector to the can gateway. Let me see if I can get you the wiring diagram.

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I sent you a PM with the diagram. Let me know if that works.

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The resistance fluctuated on both the pins rhythmically from ~80 ohms to ~120 ohms.
Thanks for the diagram I'll take a look!

Took a peek at the diagram and it doesn't appear to match my car.
It shows a 20 pin OBD II port and has pin 14 as black/violet. My connector is 16 pins.

ihredneck said:

Took a peek at the diagram and it doesn't appear to match my car.
It shows a 20 pin OBD II port and has pin 14 as black/violet. My connector is 16 pins.

Click to expand...

That's the gateway, the obd port is directly below that. It only uses a few of the actual wires.

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Just realized, you have can wires going to each door module. They often break where they bend. Not saying that is your issue, but it could happen.

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Yup, missed that section of the diagram!

I'll pull the harness out of the module and test for continuity against ground.

Yeah I checked the driver door harness and one of the wires has cracked insulation, but hasn't broke yet. I should check the others too.

I started chasing wires tonight. The three chewed on in the ECM harness that goes into the cabin go to the power supply relay, steering column electronic systems control module and accelerator pedal position sensor 2.

Possible the control module relay wire shorted against either or both of the others and toasted the steering column module or accelerator pedal sensor.

Just a thought

Okie dokie.

I have resolution! Due to a blessing of the Lord and bringing to my attention of what I should look at, I gound the culprit.

What I didn't share is I purchased this car not running right and so had no history on it.
After digging into all the harnesses under the dash and engine bay, I was led to go over the fuse panels.
So got out the Bentley (and owners manual cause the engine base fuse box diagram is wrong in the Bentley) and fuse by fuse did a check.
I found that someone had moved the 5A fuse from the F12 position for the data bus on board diagnostic interface (J533) into the F11 position that has no use.

Okie dokie.

I have resolution! Due to a blessing of the Lord after some one on one time He brought to my attention of what I should look at, I found the culprit.

What I didn't share is I purchased this car not running right and so had no history on it.
After digging into all the harnesses under the dash and engine bay, I was led to go over the fuse panels.
So got out the Bentley (and owners manual cause the engine bay fuse box diagram is wrong in the Bentley) and fuse by fuse did a check.
I found that someone had moved the 5A fuse from the F12 position for the data bus on board diagnostic interface (J533) into the F11 position that has no use.

Awesome! That would explain it!