Car stalled, no start, P1850

[Jbwoo]

Greetings folks,

My 06 Jetta with BRM, and DSG stalled / shut off the other day while driving.
Engine cranks over, fuses all good, glow plug coil light doesn't come on. So a VCDS scan reveals.
Chassis Type: 1J - VW Golf/Bora IV (1998 > 2006)
Scan: 01 02 03 08 15 16 17 19 22 29 35 36 37 39 46 47 55 56 57 75
76

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Address 02: Auto Trans Labels: 02E-927-770.clb
Part No SW: 02E 300 042 H HW: 02E 927 770 AE
Component: GSG DSG 070 0913
Revision: 04507000 Serial number: 00000509200353
Coding: 0000020
Shop #: WSC 00066 000 00000
VCID: 18313AF5280A5C8F49-5102

1 Fault Found:
18258 - Powertrain Data Bus
P1850 - 000 - Missing Message from ECU

The relay in engine fuse panel seems to actuate, and send 12v to the ECM, fans come on full speed after 1 minute of key on, then ECM gets 4.5v

Definitely at a loss as to what to do. The wiring covering to the ECM from the bulkhead has been checked of, and same with grounds near the ecm. Fuses check out with power on both sides, panel inside and in engine compartment. Any help would be appreciated.

 

[mextdi]

I googled your code and there is a possible trouble shooting:
http://wiki.ross-tech.com/wiki/index.php/18258/P1850


If your ECM or ECU is indeed dead, you can get a replacement that matches your part number and then have it sent off to get the IMMO off or your car won’t start. With IMMO off you won’t need to recode keys... Make sure you buy an Ecu that matches your having a manual or automatic.



That kind of just dying and not starting reminds me of a timing belt breaking. The engine will crank and crank and crank and won’t start. Did you check the timing belt is still there? Also, what happens if you disconnect the battery overnight and read codes after that?

 

[Jbwoo]

The engine sounds normal, can remove the oil fill cap and see the cam rotating, belt and cam were replaced 400 miles ago. ross-tech wiki is where I'm headed this morning for diagnostic flowchart stuff. I have not D/C the battery overnight yet.

Everything points to a power supply problem, or no communication between the ecm and tcm.

 

[mextdi]

One time I did my timing belt job and it wouldn’t start. Turns out the cam bolts were not tight enough and the car went way out of timing adjustment or torsion value as it is called by Vagcom values. Would crank but not start. The torsion value will only be given if the engine runs so that might not help but I would check. Otherwise try with a new used ECU with the Immo off. Get in touch with Ian at Reflect tuning, he might have an ECU you can use or buy off of him cheap. He’s an electronics guru.

 

[Jbwoo]

So lots of removing wiring harness covering to the ECM to see what I could find. The #468 Relay was triggering and ohm tested ok. Checked available voltage on the red / green power wires just before the ECM. It would get 12.5v, then immediately drop to 4.5v when the ECM would try to come online. So at that point I knew there was either an appropriate draw or short, or relay that supplies power to the ECM couldn't keep up. Removed the 460 relays under the dash and bench tested ok, and tried the bench test with a load from a test light, definitely not the load that it normally sees, and the resistance went way up. Ordered #468 relay and hoped for the best. Plugged it in and all fired to life. Bad relay, that tested ok, clicked, and then when the load was increased it would fail. Lesson is to test relays in multiple ways.

 

[bobthefarmer]

I'm glad you fixed your's with a relay. Hard to understand, but these electronic gremlins are never very forthcoming of their issues. Mine had a 460 relay issue as well. Keep one in your tool box!