Improved air purge
This TSB applies to 2011-2012 Subaru Legacy/Outback and Tribeca models. If you encounter a vehicle which has P0128 stored in memory, it may be caused by a very slight variation in coolant temperature between the left and right cylinder banks.
The slight variations can be contributed to owner driving patterns. As an example, how long an engine is permitted to warm up, heater use during cold or hot engine temperatures, etc. An air pocket within the coolant system can also cause the code to set.
A countermeasure heater hose pipe is now available that features an orifice that’s designed to regulate coolant flow past the coolant temperature sensor. The new heater hose pipe is available as P/N 14070AA361 (the old P/N was 14070AA360).
The new style heater hose pipe was used in production starting with the following VINs:
2012 Legacy VIN C*017497 (production date 12-07-2011)
2012 Outback VIN C*236992 (production date 12-07-2011)
The heater pipe is located under the intake manifold, attached by three bolts. When refilling the coolant system, be sure to follow the steps listed in the service manual to ensure that all air is purged from the system. If not, P0128 can be set again.