Water pump failure on your 2015 Toyota Highlander at 150,000 miles is within the expected lifespan for this critical cooling system component. The water pump circulates coolant throughout the engine, and its failure can lead to overheating and engine damage.
Water Pump Function
The water pump is driven by the timing belt or serpentine belt (depending on engine) and continuously circulates coolant from the radiator through the engine. It uses an impeller to move coolant. Seals and bearings eventually wear, causing leaks or circulation failure.
Symptoms of Failing Water Pump
Coolant leak from the pump weep hole or shaft seal. Whining or grinding noise from failing bearings. Engine overheating from poor coolant circulation. Coolant level dropping without visible external leak. Steam from the engine bay.
Code P0128 Connection
P0128 indicates the engine isn't reaching operating temperature quickly enough. While this can indicate a stuck-open thermostat, a water pump with a damaged impeller can cause similar symptoms by affecting coolant flow patterns. Diagnosis should consider both components.
Replacement Considerations
On the 3.5L V6 Highlander, the water pump is timing belt-driven. Water pump replacement is often bundled with timing belt service since both require similar disassembly. If the timing belt is due (90,000-100,000 miles), do both together. Expect $600-1,000 for water pump alone, or $900-1,400 combined with timing belt.