Toyota Prius Firmware 34705200.cuw: Engine Warm-Up Monitoring

34705200.cuw is a Toyota Prius engine control calibration associated with monitoring engine warm-up. Toyota service records list calibration 34705200 as a previous calibration in bulletins addressing an illuminated malfunction indicator light and diagnostic trouble code P0125.

P0125 concerns insufficient coolant temperature for closed-loop fuel control. In practical terms, the engine control system monitors whether the engine reaches the conditions needed to adjust fueling using oxygen sensor feedback. If the monitored conditions are not met, it can store the code and illuminate the warning light.

Engine control in the hybrid system

The engine controller manages gasoline-engine functions such as fuel delivery and engine warm-up monitoring. In a Prius, the gasoline engine does not necessarily run continuously, so its operation is part of a wider hybrid system that also uses electric drive. The presence of P0125 points a technician toward the engine temperature and fuel-control conditions being monitored, rather than identifying one failed part by itself.

What the service bulletins say

Toyota bulletins T-SB-0088-08 and T-TCI-3017, released in June 2008, list 34705200 as a previous calibration for the malfunction indicator light and P0125 issue. The bulletins cover 2004 through 2007 Prius models, although that bulletin-wide range does not establish that this calibration applies to every vehicle in those model years.

The revised calibration discussed in each bulletin is the one intended to address the documented concern. The listing does not establish a specific improvement introduced by 34705200 itself.