Automatic Transmission Servicing

Jan. 1, 2020
I suggest that it is a better idea to tell the customer that you did not check the automatic transmission fluid level because of whatever the reason is for that particular vehicle. 

I own two vehicles that do not have an automatic transaxle dipstick to check the fluid level. One of these vehicles is a General Motors product; the other is a Toyota product. And they are not the exception. Ford also has automatic transmissions without dipsticks as do Chrysler, Mercedes and other OEMs. The lack of a dipstick is no accident; the transmission manufacturer does not want the customer to have access to the fluid. They call it “lifetime fluid,” and it supposedly never needs changing, but it does need to be checked when there is a sign of leakage, if the transmission is having problems or if the transmission was opened for any reason. Some transmissions are so sensitive to improper fluid levels and fluid types that transmission problems or even damage can occur with the slightest under fill or over fill. 

The tube is still there, but you’ll need to order your own dipstick if you want to check the level on this trans.

If your shop is in the business of servicing or repairing automatic transmissions or if you are just performing quick services such as an engine oil change or a transmission fluid flush, you better not tell a customer that their fluid level is "OK" unless you really checked it the proper way. I have taught classes on automatic transmission diagnostics, service and overhaul for 22 years. Most technicians I have had in class (experienced or not) make simple mistakes that cause them to check the fluid improperly.

Checking an automatic transmission's fluid level properly requires four resources; access to the proper service information, up-to-date training, adequate time to perform the fluid level check and access to special tooling if required.

Adventures In Reality
My first vehicle without an automatic transaxle dipstick, a Toyota Highlander Hybrid, was purchased new in 2008. I received free oil changes every 5,000 miles for the first 75,000 miles as part of the purchase, so I had this vehicle serviced at the dealership for the last five years (83000 miles). The green-yellow-red colored multi-inspection check sheets I receive with each service always show all of the fluid levels as being OK. The problem is the fluid level check plugs appear to have never been removed, as evidenced by the factory paint marks on them.

I recently asked a technician from a different Toyota dealership what his dealership does regarding checking transmission fluid levels on vehicles without dipsticks. He said they do not check the fluid level unless there is a sign of leakage. I asked him if they mark the fluid level as "OK" on the multi-point inspection sheet the customer receives, and he said some technicians do. I told him that I thought that was a huge problem and a possible liability for his employer.

This is a GM check plug. Seems easy enough, but if the fluid temperature isn’t right you may actually let fluid out that needs to stay inside!

I suggest that it is a better idea to tell the customer that you did not check the automatic transmission fluid level because of whatever the reason is for that particular vehicle. If a customer's automatic transmission does not have a dipstick, consider selling them a proper fluid level check at an additional cost and time. Isn’t it commonplace to charge more to service some types of vehicles because of the additional expense for fluids, filters or labor? Automatic transmissions without dipsticks are an additional labor issue.

My other vehicle without an automatic transaxle dipstick, a 2002 Chevrolet Cavalier, was purchased three years ago for my teenagers to drive. I have had this vehicle serviced at a local national chain quick lube business.  The multi-inspection check sheets I receive with each service show all of the fluid levels as being "OK." The problem with the 4T45-E is the fluid level cannot be checked properly in this transaxle if the fluid temperature is above 104 degrees Fahrenheit. If you remove the fluid level check plug on this transaxle and the fluid temperature is above 104 degrees, the fluid will have expanded and it will appear to be overfilled and fluid will spill out of the check plug hole. This will actually cause the fluid level to be too low when checked properly.

I asked a technician that works for this national chain quick lube business what they do about checking fluid levels on automatic transmissions without dipsticks. He said unless there is a leak, they also mark the level as "OK" even if they never checked it. He also told me the company was making efforts to address this issue because of the many vehicles that come through their doors without transmission dipsticks.

Transmissions With Dipsticks
Let’s start our discussion with the easiest to check transmissions first. Every technician I know thinks they know how to check the transmission fluid level on an automatic transmission with a dipstick. After all, it is just a dipstick, how hard can it be?

Every time I took my car in for service, I was told my fluid level was OK. Was it really?

Transmissions with dipsticks need to be checked under the proper operating conditions. Transmission fluid temperature has always been critical for proper level checking as well as the vehicle being on a level surface. For many years the typical transmission's fluid level was supposed to be checked at full operating temperature (a minimum 180 degrees Fahrenheit), but does anyone really check the temperature of the fluid when they check its level? 

Some technicians have told me that they assume the transmission fluid is hot enough when the upper radiator hose is hot, or if the radiator cooling fans come on. I personally have run experiments on front-wheel drive vehicles. It takes about 40 minutes of engine idling before the transmission fluid temperature reaches 180 degrees while the engine thermostat opened at 12 minutes and the cooling fans came on at 20 minutes. 

My experiment on a rear-wheel drive vehicle without an electric cooling fan resulted in the transmission fluid temperature reaching 150 degrees after 60 minutes of engine idling while the engine thermostat opened and made the upper radiator hose hot at 12 minutes. Obviously, relying on the engine temperature to indicate transmission fluid temperature at an idle is inaccurate. You must actually drive the vehicle for several miles to adequately heat up the transmission fluid. Next you check the fluid temperature with a scan-tool or multimeter with a fluid temperature probe to accurately adjust the fluid level.

This is the tool used to check Chrysler and Daimler products that have a tube but no dipstick.

Some transmissions and transaxles have a dipstick tube, but no dipstick. There is a cap on the top of the dipstick tube that reads “For Dealer Use Only”. There is a special service tool universal dipstick (Miller Tool number 9336A). This special universal dipstick has a 120mm long ruler attached to a flexible cable. The ruler has increments every 10mm to read the fluid level from the bottom of the transmission pan.  The universal dipstick is typically longer than the tube and will protrude beyond the top. The level can then be compared to a temperature verses fluid level chart in the service information to determine if the fluid level is correct for that particular fluid temperature. I like this method because it lets you quickly check the fluid level over a very wide range of fluid temperatures. Be sure to read the proper vehicle specific service information for this procedure because it does vary from make to make and model to model.

On some Toyota transmissions, you have to open the thermostat valve to insure a proper fluid level check.

Transmissions without Dipsticks
When a customer brings their vehicle in for a quick service, they do not want to have to wait for more than 30 minutes to an hour. Transmissions without dipsticks typically need to have their fluid levels checked at a cold or warm temperature (between 68 and 130 degrees Fahrenheit). If a customer brings their vehicle into your shop for service with a hot transmission, you cannot accurately or safely check the fluid level unless you let it cool down first and this can take a considerable amount of time. You may even want to keep the car overnight to allow a cold start. The transmission fluid level checking procedure on transmissions without a dipstick can be a lengthy procedure. Here are a few examples just to show you how involved some models can be. That’s why I recommend that shops charge accordingly for checking and adjusting the fluid level on “sealed” trannies.

General Motors 4T40-E and 4T45-E: This transaxle is used in the 1995 and above small GM front-wheel drive vehicles. It has a 2 page long set of instructions just to check the fluid level properly. My interpretation of the basic procedure for checking this transaxle’s fluid level follows but always be sure to look up the procedure for your specific vehicle as there may be minor differences:

1.     Connect a scan tool and read the transaxle fluid temperature. If the fluid temperature is above the specified temperature for fluid adjustment, allow the fluid to cool until it is at spec. This could take several hours dependent upon the current fluid temperature.

2.     Place the vehicle on a level hoist

3.     Locate the fluid level check plug on the far right side of the transaxle just a few inches above the transaxle oil pan. Place a suitable drain container under the fluid level check plug to catch any fluid that may come out when the plug is removed. WARNING: Do not confuse the transaxle fluid level check plug with the line pressure plug that is located on the front of the transaxle, they are identical in appearance.

4.     Locate the plastic transaxle fluid fill cap that is located on top of the transaxle. Unscrew the fill plug and install a funnel in preparation for adding fluid.

5.     Start the engine and move the transaxle shift lever through all of the gear ranges stopping for a few seconds in each position.

6.     With the engine idling in the Park position, carefully remove the fluid level check plug. Be careful not to spill fluid on yourself, especially if the fluid is hot, you may get burnt.

7.     If fluid comes out of the level check hole, let it drain until it stops to a very slow drip and then reinstall the fluid level check plug. The transaxle fluid is now at the proper level.

8.     If no fluid comes out of the level check hole, add Dexron IV fluid to the transaxle through the long funnel until it comes out of the level check hole. Let the fluid drain from the hole until it stops to a very slow drip and then reinstall the fluid level check plug. The transaxle fluid is now at the proper level.

The Toyota tool makes fluid inspection and adjustment relatively painless.

Toyota AB60E and AB60F: These six-speed transmissions are used in the 2007 and above Tundra Trucks and Sequoia SUVs. They have a 14 page long set of instructions just to check and adjust the fluid level properly and a special tool (Toyota Special Service Tool number 00002-11100-02 Transmission Fill system or equivalent) is required. The transmission pan on these vehicles has two plugs, one is a drain plug, one is a overfill plug. The drain plug is the lower of the two. The procedure for this transmission is similar to the GM transaxle discussed above with the following exceptions:

1.     The fluid level check plug is in the transmission oil pan

2.     The transmission refill plug is on the left side of the transmission in a difficult to reach location. The plug has the letters “WS” stamped on its head. It can be removed with a 24 mm wrench.

3.     The fluid temperature required for proper level checking is 115-133 degrees F.

4.     Vehicles with a factory-towing package include a transmission thermostat valve that regulates the volume of fluid through the transmission cooler depending upon fluid temperature. This thermostatic valve is located on the right side of the transmission and must be pinned open during the fluid level check to insure that the cooler lines and cooler are full of transmission fluid.

5.     Adding fluid to the transmission through the refill hole is made a lot easier if you have the Toyota special tool. A suction gun can also be used to install the fluid if it is clean and not cross-contaminated with other fluids.

6.     These transmissions require Toyota World Standard “WS” fluid

Methods for inspecting and adjusting the fluid levels on “sealed” transmissions will differ from one make to another, even one model to another. Always reference the vehicle-specific service information and be sure you understand the procedure before attempting to do so. Failure to do these inspections properly may result in a transmission that is over- or under-filled, and could result in expensive transmission damage. Protect yourself, check it correctly or don’t check it at all.

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