Hybrid Transmission (EHS)

It supplies pressure when the engine is not turning. A conventional gearbox pump is driven mechanically, which is fine when the engine always runs, and useless in a hybrid that moves on electric drive alone with the engine stopped. The electric pump takes over in those periods, keeping clutches applied and components lubricated. Its failure produces a distinctive pattern: faults and harsh behaviour during electric operation, with everything apparently normal once the engine starts, which is a useful diagnostic clue.

Some transition is normal, and a change from how the vehicle used to behave is not. Harshness that has developed can come from clutch wear, from pressure problems traced to the fluid or the electric pump, from engine or drivetrain mounts that have perished, or from a control calibration that needs adaptation after other work. Have the codes read and the fluid checked before assuming the transmission is at fault, since mounts and fluid are far cheaper places to start.

Specialist rebuilders handle some units, and the manufacturer route is an assembly. The unit contains gears, clutches, two electric machines and their cooling in one housing, so diagnosis to component level requires equipment and data that few workshops hold, and reassembly demands cleanliness discipline because the electric machines share the housing with the oil. Where a rebuild service exists it can make sense on cost. Where it does not, the assembly is ordered by OE number and quoted.

Exactly what the manufacturer specifies, and the requirement is stricter than for a conventional gearbox because the fluid is in contact with electrical windings and insulation. A fluid with the wrong electrical properties can lower insulation resistance and set a high voltage fault even though it lubricates perfectly well. Quantity and fill procedure matter too, since many units are filled to a level at a specified temperature. Use the correct product and follow the procedure rather than approximating.

Because the control strategy has decided it must, and the reasons are usually external to the transmission. A pack that is cold or low in charge, a fault limiting electric drive, high ancillary loads such as cabin heating in winter, or simply a driving pattern that gives regeneration little opportunity will all increase engine running. If the change is sudden and unexplained, have the codes read, since a limited component reports itself long before the behaviour becomes obvious to the driver.

Think of this category in two halves. The serviceable items, acoustic packs, seals and the electric oil pump, are modest purchases that fit within an ordinary repair budget. The complete hybrid drive unit belongs with the most valuable assemblies on the vehicle and is normally handled by quote rather than shown with a standing figure. The category spread is published in the strip at the head of this page. Spend on diagnosis first. Fluid condition and pump output explain a large share of shift complaints and cost very little to check.

Fluid level checks and inspection are reasonable where the procedure allows. Anything involving the unit itself is not, because these transmissions contain high voltage machines, require isolation before work and coding afterwards, and are heavy enough to need proper lifting equipment. The electric oil pump may be externally mounted and accessible on some designs, and even then the high voltage and coding considerations apply. Have the diagnosis done properly and order against a confirmed fault.

More than on a conventional car, because the noise environment changes constantly. When the engine is stopped the drivetrain is nearly silent and gear whine, pump noise and inverter tones are fully exposed, then the engine starts and masks them again. Acoustic packs are tuned for exactly that situation. Leaving one off after a repair produces a vehicle that sounds coarse in electric mode, which owners notice immediately even though nothing mechanical has changed.

Only where the OE number and the software variant agree. Hybrid transmissions are matched to a specific engine, a specific pack voltage, specific ratios and a specific control calibration, and units that share a family name frequently differ in all four. A mismatched unit either refuses to code or behaves incorrectly in ways that are hard to diagnose afterwards. Quote your vehicle identification number and have the reference confirmed before anything is dispatched.

There is no fixed expectation, and the components that limit life are the ones you can influence: fluid condition, cooling and the health of the electric oil pump. Because the electric machines take much of the load that would have gone through gears and clutches in a conventional automatic, the mechanical parts often see gentler duty than their equivalents. Follow the fluid interval, investigate faults promptly rather than driving through them, and the unit is not a scheduled expense.

Not in a way that shortens its life meaningfully. Regeneration runs torque back through the same gears in the opposite direction, within the envelope the unit was designed for, and it reduces wear elsewhere by taking work away from the friction brakes. What it does change is the loading on the drivetrain mounts, which now react torque in both directions frequently, so a hybrid with a clunk on lift off is more likely to need mounts than transmission work.

Yes. Complete hybrid transmissions are quoted rather than priced, and that is the sensible way round for an assembly of this size and value, because the reply confirms availability before a workshop books time for the swap. Send the number from the unit and the vehicle identification number. Ask about the smaller items in the same message. Electric oil pumps, seals and the acoustic pack are frequently the actual fault, and a shift complaint traced to fluid condition or a pump costs a small fraction of what a replacement transmission costs.