Doosan DA30 with ZF 8EP 320 Transmission goes into neutral whiles driving.

[Brian Bobb]

Presumably the gear shifter is giving digital signals to VCU (vehicle controller), which gives CAN signals to TCU.

So something is telling the tcm to go into neutral while driving. I've already checked from the gear shift and everything is good from that end to the vc3. I will check the wiring from the vc3 to the tcm and transmission. Is there anything else that can cause the transmission to go into neutral while driving?

 

[Bigbert]

Hi Brian,
are you able to share TCU number/code?
And have you any chance to get a readout of fault memory of TCU/ECU/VCU?
Possibly the output speed signal is sometimes faulty. But this one is wired up internally. So not quite easy to fix in truck.

 

[Brian Bobb]

Hi Brian,
are you able to share TCU number/code?
And have you any chance to get a readout of fault memory of TCU/ECU/VCU?
Possibly the output speed signal is sometimes faulty. But this one is wired up internally. So not quite easy to fix in truck.

I will attach the TCU info. I wasn't able to get a scanner as yet to pull the codes. Should be getting one later this week. So if it is the output speed signal, the entire transmission has to be taken out to get access to it?

 

[Brian Bobb]

Presumably the gear shifter is giving digital signals to VCU (vehicle controller), which gives CAN signals to TCU.

Due to the adapter for the scan tool taking a while to come, we had someone come to test the pressure of the transmission and it turns out that the converter was losing its pressure.

 

[Bigbert]

Brian,
I'm not sure what came first? Hen or egg? Losing converter pressure: Is it lockup clutch (LUC) pressure? Or converter back pressure? Presumably lockup as converter pressure is created via mechanical spring and piston.
The question is: Does LUC disengage due to transmission going to N (A) or vice versa (B)? Rather situation A.
I'll share a few pics from output speed sensor in a conversation. Space in DA 30 is pretty tight, so not sure whether you'll have easy access.

 

[Brian Bobb]

Brian,
I'm not sure what came first? Hen or egg? Losing converter pressure: Is it lockup clutch (LUC) pressure? Or converter back pressure? Presumably lockup as converter pressure is created via mechanical spring and piston.
The question is: Does LUC disengage due to transmission going to N (A) or vice versa (B)? Rather situation A.
I'll share a few pics from output speed sensor in a conversation. Space in DA 30 is pretty tight, so not sure whether you'll have easy access.

Thanks for the response. I was not at work the day the guys came to hook up the pressure gauge to say that it was the converter that is losing pressure. Apparently they did not specify if it was the lock up or back pressure. The thing is, the truck is still running without any issues so far.