I have a 2003 VW Beetle Convertible with a 6 speed auto transmission it start to shift hard when the car warms up. do i need a new trannsmisson or is it just a sensor?

May be two. One on trans and the other on rear diff.

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2003 Volkswagen New Beetle Workshop Repair Service Manual PDF Download

I hope your problem will be solved :))

IF YOU HAS GAS ENGINE USE API CERTIFIED FOR GAS ENGINES USE 5W 30 FOR COLD WEATHER. YOU CAN USE 5W 40 FOR WARM AND HOT CLIMATE. FOR DIESEL ENGINE YOU NEED API SERVICE CF4 OR CG4 USE MOBILE 1 OIL 5W 30 COLD WEATHER AND 5W 40 FOR HOT CLIMATES ALSO CHECK IN OWNERS MANUAL.TO BE ON THE SAFE SIDE OR ASK THE AUTO PARTS SALESPERSON TO LOOK UP TYPE OF OIL YOU SHOULD USE TO KEEP FROM DAMAGING THE ENGINE IF YOU HAVE TURBOCHARGER.

When was last time trans fluid & filter were changed? Should be done every 50k. That's where I'd start.

WELL BOTH TRANSMISSIONS IS 6 SPEED TRANSMISSION USED ON TURBO GAS AND TURBO DIESEL ENGINES.HFZ AND GHE TRANSMISSION CODE.1.9

As you see in the first illustration. you can use your key to pry open the cover. It may or it may not contain the fuse locator card.

go to a trans shop and get them to change the filter in the trans ... this may be cheap at first!

all vw cars have a computer on board that controls a fuzzylogic gearbox.the racier you drive the higher the revs before upchange and vise versa ie low/low change so the harder you drive the more noticable the gearshift will be in auto mode.manual mode will always be jerky compared to a std auto box.THE JOYS OF NEW TECHNOLOGY.....

Automatic? 6 years old. It is probably low on fluid and/or it needs serviced(oil/filter).

On some volkswagen Transmissions you can reset the computers shift plan by doing the following. Starting with car off in park, turn ignition to ON (but do not start) then depress the gas pedal for at least 3 seconds, then shut the car off, start and drive. This resets the computer's shifting plan for some VW's and you can expect some hard shifts after this reset, but it may help with funny shifting. The afore stated speed sensor is also a possible culprit.