Automatic transmissions are like a mystery to most motorists. All they ever know is that they move their gear selector in “D” for Drive and their car goes forward, they put it in “R” for Reverse and it goes backward, and they put it in “P” for Park when they shut the engine off. They may understand that the transmission needs some kind of fluid, but have probably never inspected the level or even looked for the dipstick unless they drive an older car with a leaker. So if the transmission begins to slip, shift oddly, makes noise or misbehaves, most motorists do not have a clue as to what might be creating their issue, nor do many technicians who are not transmission experts.
Automatic transmissions system are a complex and wonderful thing when they are functioning properly. But when internal issues cause the transmission to act up, it takes a fair amount of expertise and experience to diagnose the fault. If the issue is not low fluid, a faulty solenoid, valve body or controller, the transmission often has to come out for a tear down and inspection. This can be a time-consuming process, so many shops simply change the transmission when there is a major internal issue rather than trying to repair or rebuild it themselves.
Rebuilding automatic transmissions is an exact science that needs familiarity with the unit being rebuilt as well as the the correct parts, tools and specifications. If you do not get it right the first time, you wil certainly get the opportunity to do it over again. That is why many transmission shops today no longer rebuild transmissions themselves. There are too many different makes and models. The shop can make more money changing transmissions with a reman transmission sourced from an outside remanufacturer than rebuilding the units themselves. A typical FWD transmission job today can easily run $2,000 to $2,800 or more for components and labor.
Some independent repair garages that do not usually do transmission repairs often refer customers who are having transmission issues to a transmission shop. Other shops may change the transmission, but do not actually overhaul the transmission themselves. They purchase a remanufactured transmission from a transmission supplier.
A TRANSMISSION FLUID LEVEL & LEAKS
One of the most common complaints with automatic transmission is fluid leaks. Fluid can leak out of the driveshaft seals, the input shaft seal, the transmission pan gasket, the torque converter or the ATF cooler and line connections. If the fluid level becomes low, the transmission may be slow to engage when it is shifted into drive. Gear shifts may be sloppy or delayed, or the transmission may slip between shifts. If the fluid level is very low, the transmission may make the vehicle to not go at all.
On most cars, the fluid level should be inspected when the fluid is hot with the engine idling, the parking brake set and the transmission in Park. If fluid is required, add only enough ATF to bring the level up to the full mark. Do not overfill because doing so can cause the fluid to become aerated, which may impact transmission operation.
If the dipstick reads low, the transmission is maybe leaking. So look underneath to see where the fluid is going. If there are no visible leaks, inspect the radiator for ATF in the coolant. The ATF cooler inside the radiator may be leaking and cross-contaminating the fluids.
You should equally check the condition of the fluid. Some discoloration and darkening is normal as the fluid ages, but if the ATF is brown or has a burnt smell, it is badly oxidized and requires change. Varnish on the dipstick is another sign of worn out fluid.
You can equally do a “blotter test” to check for worn fluid. Put a few drops of ATF on a paper towel and wait 30 seconds. If the spot is widely dispersed and red or light brown in color, the fluid is in satisfactory condition. But if the spot does not spread out and is dark in color, the ATF is oxidized and should be replaced.
Many transmission experts say most transmission problems can be prevented by replacing the ATF and filter regularly for preventive maintenance. How often depends on how the car is driven. For some cars, this might be every 30,000 miles or two years.
The harder your transmission operates, the hotter the fluid runs. The life of the fluid drops quickly once its temperature gets up above about 200 degres F. Installing an aftermarket auxiliary ATF cooler that is parallel to the OEM ATF cooler is recommended to keep fluid temperatures down on cars that are used for towing or are driven hard.
ATF also becomes contaminated with normal wear particles from the clutch plates, bushings and gears. The filter will trap most of this debris before it can create problems. But many older Asian transmissions only have a plastic or metal screen that does little to protect the transmission against internal contaminants and nothing to keep the fluid clean. On these cars, changing the fluid is the only way to get rid of these contaminants.
USE THE KIND OF TRANSMISSION FLUID SPECIFIED FOR YOUR TRANSMISSION
When including or replacing ATF, use the type specified by the car manufacturer. GM, Ford, Chrysler, Honda, Mercedes and others all have their own specifications for ATF. There is no such thing as a “universal” ATF that works well in all transmissions. Many universal fluids do meet a variety of specifications, but no one product can meet all OEm requirements due to the different friction additives that are needed.
Ford has three automatic transmission fluid specifications: Type F (a non-friction modified formula for most 1964-81 transmissions), Mercon (a friction modified ATF similar to Dexron II for 1988-97 transmissions), and Mercon V (Fords latest friction-modified formula, introduced in 1997).
General Motors has produced Dexron II, III and VI. These are friction modified formulas. Dexron III can be used in the older GM transmissions that originally required Dexron II. Dexron VI was introduced in 2006 for GM Hydra-Matic 6L80 6-speed rear-wheel-drive transmissions. Dexron VI now takes over Dexron III and II, and can be used in GM or import transmissions that formerly specified Dexron III or II.
Chrysler has a number of different ATFs: MS-7176D (also known as ATF+2) is Chrysler’s version of a friction-modified ATF that is similar to Dexron II. But Chrysler’s fluid is more slippery than GMs, so Chrysler recommends using only ATF that meets their specificationss in Chrysler transmissions. In other words, do not use Dexron or Mercon in a Chrysler transmission.
Chrysler MS-7176E (also known as ATF+3) was introduced in 1998 and supersedes ATF+2. It should only be used in 1998 and newer Chrysler transmissions, but can equally be used in earlier Chrysler transmissions.
Chrysler ATF+4 is for 2000-01 model year applications, and their newest fluid ATF+5 is for 2002 and newer models.
TRANSMISSION FAULT CODES
If a cars Check Engine light is on, it means the computer has detected a fault and has set a diagnostic trouble code. There is no way to determine if it is an engine code, transmission code or body code, so you will have to plug a scan tool or code reader into the diagnostic connector to extract the code.
If the transmission OD (overdrive) light is on or flashing, it implies the transmission controller has diagnosed an internal transmission fault. To diagnose the issue, a scan tool that can read transmission codes must be plugged into the vehicle diagnostic connector (usually found under the dash near the steering column). The scan tool will then display the transmission code(s) that turned the warning light on. What happens next depends on the code. If the code indicates an internal performance problem, the transmission will probably require the attention of a specialist. But if the code shows an electrical fault, a bad sensor or solenoid, you may be able to fix the issue without having to take your car to a transmission shop.
Electrical fault codes are set when the transmission controller or PCM senses an open or a short in a shift solenoid, shaft speed sensor or other device. Performance codes are set when the computer sends out a command, such as a 2-3 shift, but the transmission does not respond properly.
With electrical codes, you can use a DVOM to test a solenoids resistance. If the solenoid is open, shorted or out of specifications, it needs to be changed. Performance codes, on the other hand, need further diagnosis and can themselves be caused by electrical faults in sensors.
Electronic transmissions use speed sensors to monitor shifts and what is going on inside the transmission. When things do not match up properly, a “ratio error” fault code may be set indicating something is wrong with the way the transmission is shifting gears. This may make the transmission to go into the default or limp-in mode, which typically turns all the solenoids off and leaves the transmission in 2nd or 3rd gear.
The only way to identify these kinds of transmission faults is to follow the diagnostic charts for the particular code(s). Ratio error codes often turn out to be caused by a fault in a shaft input or output speed sensor.
Irrespective of what the code says, it is a good idea to check for any OEM technical service bulletins that might relate to the code or the complaint. Many times you will discover the fix in the TSB, which may require replacing a certain parts or even reprogramming the transmission computer.
Some Chrysler transmissions, for example, can have a “bump shift” condition. There is nothing wrong with the transmission, but the computer needs to be reprogrammed to recalibrate the shift points. In Chrysler three-speed automatics, changing the fluid to ATF+3 can equally help eliminate harsh shifts.
Some transmission problems may need “retraining” the computer. This is also necessary if an electronic transmission or computer has been changed. Chrysler TSB 18-24-95 describes the retraining procedure that lets the computer to relearn the correct shift points.
- Disconnect the battery to clean the computer’s memory.
- Reconnect the battery and start the engine.
- Drive the car while trying to maintain a constant throttle position as it accelerates up through all four gears. If the transmission is shifting properly, it should be in 4th gear by the time you reach 45 to 50 mph. Repeat this procedure from a standing start 15 to 20 times.
- With the car traveling at less than 25 mph, do five to eight wide open throttle kickdowns to get the transmission to downshift to 1st from 2nd or 3rd gear. Drive in 2nd or 3rd gear for at least five seconds between kickdowns and remember to kick it down only when you are going less than 25 mph.
- While riding at 45 to 50 mph, do five to eight part to wide open throttle kickdowns to either 2nd or 3rd from 4th gear. Again, keep driving for at least five seconds in 4th gear inbetween kickdowns.