2007 VNL 780 Switching In and Out of Auto/Manual

check ALL your grounds, 1 bad ground will wreak havic on anything electrical

 

BS about grounds, exuse me))))

Really ZF Astronic switches to manual loosing J1939 axel speed data form MID 136 (brake system).

Pull the ZF codes and you will see missed J1939 messages. So scan ABS unit for fault codes.

Usually it is ABS sensors ore CAN/Datalink J1798 wiring issues

 

OK.... excuse me, I'll keep my BS to myself next time.

 

I'm sorry, I was not polite, really.... You are expirienced trucker and really many trucks got problems with wiring, especially MAN (F2000 and TGA). Many, really many problems are related with bad ground wires. And I used to see ZF transmission problems with bad grounding.

Volvo is the different thing. They use European transmission made for trucks with 24V electrical system. So to install it in US truck 12-24V converter is used. When its grounding is bad TCU fails to start up and truck wont moving!

I'm sure it is J1939 data issue, like ABS wheel speed data, ore TCU output shaft speed problem. But not grounding

Why I think it is ABS problem? Volvo use frame mounted ABS unit by wabco. CAN line runs along left frame rail in corrosive conditions.

 

any update?

 

Hey, you got any response on the matter, I have the same problem, if possible, let me know news. I have observed that when cold it does, when temperatures begin making the problem

 

Plz pull fault codes from ECU (MID128), VECU (MID144), TCU (MID130) and ABS (MID136). All codes are important.
Better erase all codes with dashboard computer and when problem appeares, pull codes and post a list