Automatic Gearbox Fluid (ATF)

What is a Automatic Gearbox Fluid (ATF)?
Automatic Gearbox Fluid or Automatic Transmission Fluid (ATF) is specifically designed for use with auto gearboxes. It's an oil based fluid with additives that make it particularly good at maintaining and protecting the parts inside the gearbox.
What problems can be caused by this part?

Gearbox temperature warning light showing on dashboard

There is a light similar to the one pictured here showing up on the dashboard. Different manufacturers sometimes have slightly different warning light symbols but it should be similar to the one pictured.

Gearbox makes grinding sound

When changing gear the gearbox makes a loud grinding noise. This will be a more common occurrence on cars with manual gearboxes but can also happen with automatics. There can be various reasons for it but it always presents as a loud, unpleasant sound of mechanical scraping/grinding.

Gear changes are difficult

Changes between gears have become difficult, the gearstick no longer moves freely between gears, it sometimes seems to get stuck or won't go into a gear properly.

How much does it cost to replace the Automatic Gearbox Fluid (ATF)?
The gearbox fluid itself isn't particularly expensive, expect to pay between £10 - £20 per litre depending on the brand/quality. Replacing the oil will usually take up to an hour of labour so factor that in to the cost, an average cost would be £100 - £200. This will obviously depend on the labour rate of the mechanic you use and the oil amount required by your make/model's gearbox.
We have 104 owner problems that mention the Automatic Gearbox Fluid (ATF)