GMC Sierra Auto Transmission Slipping

Overdrive does not work and take-off is very slow unless I manually shift from 1st to 2nd then 3rd. I had a GMC service center flush the Transmission and Torque Converter and change the fluid in both the Transmission and the Torque Converter about 5000 miles ago. The service manager said it would no be necessary to change the filter as the Transmission is being flushed. I just noticed that the Transmission fluid level is about six inches over on the dipstick. In addition, I am also slightly sensing a burning oder. I hope this is something that can be fixed with out having to have the Transmission rebuilt.

I had Autozone check Service Engine Soon code. Got code P1870

Transmission Component Slipping.

Explanation: Transmission is in 4th gear with TCC engaged and the ECM has detected excessive slippage when comparing the input shaft speed to the output shaft speed.

Probable cause:

#1 Tailor towing may set code.

#2 Check transmission fluid level.

#3 Internal transmission fault.

Repairing the above will fix the following.

Code P0758


2-3 shift solenoid valve performance


ECM has detected an open or shorted condition on the shift solenoid circuit an open or shorted condition on the shift solenoid circuit.

Probable cause:

#1 Shift solenoid failure-repair Repair other codes first.

#2 Open or short circuit condition

ANSWER: An 1870 code is always something slipping inside the trans, which would explain your problem at take off. I usually do NOT recommend transmission flushes on older vehicles with a lot of miles. Unfortunately, you’re looking at the trans having to come out and get rebuilt. Good Luck!

GMC Envoy Transmission Fit

Will a 1999 Tahoe Transmission fit in a 2000 Envoy?

ANSWER: No it will not. The bellhousing on each transmission is different, due to different engine combinations. It won’t work. You could use a transmission out of an S10 Pickup or S10 Blazer assuming they have the same engine as your Envoy.

Overfill Fluid

Is it possible to overfill transfer case to the point of it leaking out a small hole to the right of fill plug.

ANSWER: Yes, you can easily overfill the transfer case, especially if you don’t know what you’re doing. I’ve seen this quite a bit. Just take out the fill plug and let it drain until the fluid is level with the opening, then reinstall the plug.

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