Many modern automatic transmissions have no dipstick. Instead, they are checked through a level or check plug on the transmission case, with the vehicle level, the engine running and the fluid at a specified temperature, usually read with a scan tool. When the fluid is at the right level, a small stream just trickles from the check hole. Some designs have a capped fill tube that needs a special dipstick tool. The exact procedure varies by transmission, so follow the service information for yours.
How to check transmission fluid without a dipstick
- Park on level ground; on a lift, the vehicle must be level side to side and front to back.
- Start the engine and let the transmission reach the temperature range in the procedure, using a scan tool to read fluid temperature.
- With the engine running and the shifter in the position the procedure specifies, remove the check plug.
- If fluid trickles out steadily, the level is correct; let it slow to drips, then refit the plug with a new seal if specified.
- If nothing comes out, add the correct fluid through the fill port until it does.
Why temperature matters
Transmission fluid expands as it warms, so a level checked cold or too hot is misleading. Sealed units are designed to be checked in a narrow temperature window; checking outside it is a common cause of overfilling or underfilling, which can cause slipping, harsh shifts or foaming; see transmission fluid temperature.
Which transmissions have no dipstick?
Many late-model GM, Ford and other automatics, including several six-, eight- and ten-speed units, use a check plug instead of a dipstick. Others keep a dipstick or use a tube with a cap. If you are not sure which you have, see what transmission do I have?
Overfilled or underfilled
Too little fluid lets the pump draw air, which causes slipping and heat. Too much fluid can be churned into foam by moving parts, which also causes slipping and can push fluid out of the vent. If fluid pours out of the check hole rather than trickling, let it drain to a trickle at the correct temperature; if nothing comes out, add fluid slowly.
Use the right fluid
Sealed transmissions are particularly sensitive to fluid type. Use exactly the fluid the manufacturer specifies; see transmission fluid chart and transmission fluid types.
Signs the level is wrong
- Slipping, delayed engagement or harsh shifts; see transmission slipping
- Fluid leaks under the transmission; see transmission fluid leak
- Overheating warnings; see transmission overheating
If your transmission has a dipstick
See how to check transmission fluid for the dipstick method, and how often to change transmission fluid for service intervals. Many owners leave sealed-unit checks to a shop because of the scan tool and lift needed.
More guides: how much transmission fluid do I need?.
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