Hey all!


It runs up to the top of the transmission and connects to the tramsission chassis, with a y splitter, and runs up towards the engine to another cut end.
I have a 2008 silverado wt

I'm throwing a p0787. Both solenoids should be good now. Noticed a hose connecting to the top of the transmission and split with a Y fitting running forward to nowhere and the other end backward to nowhere.

I had been leaking transmission fluid slowly, so filled it with sealer, only to discover that when the truck is running, it drips out of the end of the hose. So it's only reasonable to assume that these open hoses leading into the transmission chassis are likely causing a pressure loss and therefor a voltage drop.

Curios what it is. If I\m off base. Why is there even a hose on the top of the transmission at all, like what's its purpose? The fluid cooling lines are hard piped and running to the radiator, so I'm at a loss. If someone could help educate me it'd be hugely appreciated. Google searching isn't working.

 

Please provide year, engine, chassis type (1500/2500/3500 w/ or w/o 4x4) and transmission model/RPO code for further details on troubleshooting the P0787.

The tubes are case vents for the transmission and transfer case (if equipped). Same principle as axle vents and, to some degree, the engine’s PCV system.

 

For sure, I apologize.. Transmission just says 4 speed automatic
2008 silverado 1500 wt
6cyl
2wd

 

1) I forgot to mention it before, but if there’s fluid dripping out of the hose, it’s probably because the vent fitting is getting plugged up - as that happens, pressure builds in the case and it can push more oil mist out of the vent hose. Disconnect the hose from the transmission and clean the fitting as best you can (pipe cleaners work well), then blow compressed air through the hose before reattaching it to the vent.

2) P0787 indicates the TCM isn’t detecting a change in voltage when commanding the 3-2 shift solenoid off. It expects to see the voltage level return to charging voltage but instead it remains at or near 0. This could be due to a bad circuit connection or faulty TCM. If you’re not skilled with a multimeter, I’d recommend taking it to a transmission shop.

One common problem with these transmissions is the seal in the wiring harness starts leaking ATF into the connector and causes short circuits. Disconnect the 20 pin connector at the transmission and inspect for ATF - if present, the internal wiring harness will need replacement.

 

This is incredible! Thank you!!

Life is hitting pretty hard, so a shop is out of the question unfortunately. This give's me a few things to try.

Much appreciated!

 

I understand the need to DIY repairs - and I certainly don’t condemn anyone that needs to do it - as I’m quite familiar with the need as well, so I’ll do what I can to walk you through it as you need it.

The next step (if the connection is dry) is to back probe the circuit at the TCM and watch the voltage as it’s being driven and works through shifts. Depending on which shift is being performed will determine what you see on the meter.

The circuit you need to watch is circled in red.


2008 Silverado 1500 4.3 w/ 4L60