: 2000 DHS transmission light on

05-11-13, 08:47 AM
I was driving my deville on the highway for a while when the "service transmission" alert came on. I hadnt had any issues with hard shifting up until then. When the light came on, the automatic transmission started shifting hard when going into 2nd gear. I ran the codes myself which cleared the code and now it shifts fine. Error code p0734 was the code that came up which indicated slipping in 4th gear (I haven't noticed any issues with fourth gear). Any thoughts?

05-11-13, 09:00 AM

05-11-13, 10:21 AM

Help us help you and always post the code definitions along with the codes. No one has them memorized.

05-11-13, 01:42 PM
Hey...the part where i said it mentioned the issues with 4th gear is what the code meant. I dont seem to have an issue with 4th, i only noticed it in 2nd.

05-11-13, 02:14 PM
The first and last time I saw "Service Transmission" on my deville, it eventually had to have the unit replaced.....

I don't want to ever see that message again

05-11-13, 06:29 PM
By unit what are you referring to? The solenoid?

05-12-13, 05:25 AM
He means the whole 4T80E unit. Same experience here.

If it shifts fine and the code is not returning, pray that it never comes back. If the "Service Transmission" message and a code is set, your PCM will command full line pressure on the transmission, that's likely why you experienced sudden harsh 2nd shift.

Fluid too old or contaminated? Incorrect amount? Debris in the system? I'd drain and refill trans fluid, and clean the screens and the magnet, even if the code does not come back.

05-12-13, 11:17 AM
That makes sense, thank you so much for the help!

05-15-13, 10:30 AM
So your shift solenoids fail. Yo will get a service trans message? Or is the message for changing fluid based on miles or severe conditions? Never had a solenoid go out. Assume if trans is not shifting right you will get a code but not the service message?