The P0700 code in your 2017 Toyota Sienna indicates a general transmission control system malfunction, while the slipping in drive suggests mechanical issues within the 8-speed automatic transmission (A960F). P0700 is an informational code—additional transmission-specific codes will identify the precise issue.
Understanding Transmission Slipping
Slipping occurs when the clutch packs that engage gears don't hold properly. You may feel the engine rev without proportional acceleration, a sense of "slipping" through gears, or delayed engagement. This indicates clutch pack wear, low line pressure, or solenoid issues affecting gear engagement.
The 2017 Sienna Transmission
The 8-speed automatic in your Sienna is Toyota's DirectShift design, offering smooth shifts and good fuel economy. Like any automatic transmission, it relies on proper fluid condition, pressure, and clutch pack health. Minivan duty cycles—frequent short trips, city driving—can be demanding on transmissions.
Common Causes
Low or degraded transmission fluid affects clutch engagement. Worn clutch packs can't maintain grip under load. Shift solenoid issues affect gear engagement. Valve body wear causes pressure inconsistencies. Torque converter clutch problems can feel like slipping.
Diagnostic Approach
Retrieve all transmission codes with Toyota Techstream—P0700 alone doesn't specify the issue. Check fluid level and condition immediately. Monitor line pressure during operation. Note which gears exhibit slipping—this identifies affected clutch packs. Test solenoid operation.