Clutch & Transmission Technicians
If you have 4WD Chevrolet or GMC Diesel Truck with the Allison Transmission, we recommend reading this article.
This article addresses a code PO735, typically after driving at higher speeds. May also have a trans overtemp code.
Conditions that usually set code: This code will usually set when you are driving at higher speeds and you feel the transmission down shift or neutral out, followed by a check engine light. It can also set when pulling a trailer at freeway speeds, then accelerating to pass. This tends to happen more on vehicles that are used for towing and or have been modified for extra horsepower. When this code sets. It puts the transmission into a fail safe mode and will eliminate 5th gear and lockup. This will cause the transmission temperature to rise and get hot. We recommend pulling over as soon as possible and not driving like this or damage to the transmission could occur.
Immediate action: We recommend pulling over to a safe place and checking for codes. If you get a code PO735 5th gear ratio. We recommend writing the code down for future reference and clearing the code. ( We recommend buying a code reader and keeping it in the vehicle for this purpose. One that can also clear codes) Check your transmission fluid condition and level. If the fluid level is good and the color is a clear pink and does not smell burnt . Then check the transfer case fluid. This will require getting under the vehicle, so only do so if the vehicle is in a safe place to do so and is secured from rolling. If the transfer case or transmission fluid is low or burnt. We recommend towing vehicle to the nearest shop.