Vehicles equipped with an automatic transmission and a start-stop function require an oil volume accumulator (HIS) to maintain transmission oil pressure while the engine is stopped. This component is key to ensuring the vehicle can start up dynamically immediately upon engine restart. Many high-performance saloons and SUVs rely on the ZF eight-speed automatic transmission 8 HP, which uses the oil volume accumulator for smooth start-stop functionality.
Despite the 8 HP’s reliability, oil ageing and thermal stress can cause damage to the accumulator over time. Defects are typically identified through symptoms such as:
- Failure of the start-stop function
- Error messages in the vehicle display
- Increased fuel consumption
- Reduced engine power
Due to the repair-friendly design of the ZF 8 HP, damage to the accumulator does not require a full transmission overhaul. The component can be individually replaced after dismantling the oil pan. ZF Aftermarket is now supplying the necessary spare part, in proven OE quality, to the independent aftermarket as a separate, cost-effective repair solution.
The entire transmission, including the oil volume accumulator, suffers from oil ageing as protective additives degrade under pressure, shear forces, and thermal load. This degradation reduces lubricating performance and increases stress on components.
Therefore, ZF Aftermarket strongly recommends regular transmission oil changes based on driving profile and operating conditions. A timely oil change reduces wear on clutches and valves, ensures consistently smooth gear changes, and extends the service life of the transmission, ultimately preventing expensive repairs.
