I've had two related issues for about a month now with our 2011 Chevy Volt.
Issue 1: The situation is that when the ICE kicks on after the electric range in either normal or mountain mode goes to zero, the engine seems to struggle to produce adequate power to keep the batteries sufficiently charged and maintain speed. At highway speeds (say 65mph+) the engine will start to over rev (probably 1500 higher than the normal high range of engine) in an attempt to produce more power. After a few seconds at this unusually high RPM range, a "Propulsion Power is Reduced" message appears. At this point, the car will continue to rev very high even if the speed is reduced to 25-30mph. If the car is parked and the battery is allowed to charge for several minutes, the messages go away and the car will drive normally at speeds below 65mph.
The DTC codes associated with this event are always P16E0 and P0AC4. I've also occasionally gotten a P0101 (MAF sensor) if I continue to push the engine a little longer, but I think that's a secondary result caused by the engine over revving and not the underlying issue.
Issue 2: Around the same time the above issue started, the MPG in ICE mode suddenly plummeted from 35-40 to 25-30.
P16E0 is "no torque detected," but clearly the engine is still producing some power, just not all of it is getting to the battery or the wheels. I've only found a few references to the P16E0 code and no solutions. Given the issues I'm experiencing, I'm suspecting it could be something to do with clutch 2 in the "1st generation" diagram on the attached link.
By Jeff N, Patrick Groeneveld and George Bower Preface This article is based on a GM patent US 8,602,938 , issued in December 2013, and presentations by GM at an SAE vehicle electrification conference on February 11, 2015 in Los Angeles. The presentations by GM verify that the patent...
If there was an issue with clutch 2, the engine would still be capable of producing 55kw via motor A to charge the battery, but wouldn't be able to connect to the planetary gear and therefore not be able to recharge the battery using the 111kw from motor B. This would seem to explain the lack of power and mpg even when the engine seems to running normally (not loud, rough, or excessive exhaust) with no codes presenting.