Most vehicles nowadays use electronic controls to operate your vehicle's automatic transmission. Try this: when your vehicle shifts from a low gear like 1st or second gear, a device controlled by your engine computer uses a shift solenoid to automatically shift the transmission to your 3rd, 4th and 5th gear. And this is the same when the transmission goes to overdrive which helps the vehicle saves gas when cruising. This system is fine and dandy but what will you do when the same electronic system starts to falter? This brings us to the original question which ask you the vehicle owner... what to do when your transmission (trany) service light starts showing up in your dash panel?
Generally speaking, a transmission fault code is shown by flashing your dash panel indicators showing "overdrive" or "OD"; "service" or "traction" lights when there is a trany failure. When these happen, there is no need to panic. If you know the basic trany troubleshooting techniques, you should be able to deal with it and avoid being plunged to an expensive garagerepairs that are mostly unnecessary. Shown below are some of the important trany information you need when dealing with a trany flashing lights.
1.) Get the trany code of the flashing light.
You can do this by seeing your nearest local parts store so they can scan the code for you. This kind of service is normally offered for free and all you have to do is visit any of these parts store. If you like, you can buy inexpensive code scanner available in the Internet so you can check the codes yourself. This way, you can start troubleshooting at any time and place convenient for you.
2) Call your local vehicle dealer for the vehicle service bulletins
If your vehicle has any free upgrades from your vehicle dealer, a quick phone call to them will confirm that. Normally such warranty service is offered for free even if you are not the original owner of the vehicle (most vehicles warranty is carried by the vehicle not the owner). This step can save you some money especially if the vehicle needs a computer upgrade or replacement which can cost you a lot of money if you pay a garage to do it for you.
3.) Confirm the trany fault code by writing down the symptoms
To check, find out the actual defect of the transmission: Is it in LIMP mode? Limp mode is a trany shift mode where your transmission is stuck to a low gear until the trany problem is fixed. Is the trany light flashing on all the time? (if not it is called intermittent), Does it comes on when you hit a bump? Shows up when the engine is cold? Is the trany shifting harsh? How is the trany fluid? Does it smell burnt? What is the color? You need to jot down all these symptoms so that when you start searching for the fix, you can use these info with the code related to it (same after you fixed it, so you can confirm if the fix is really done or not). Example: if the trany code light only comes when you hit a bump in the road, it shows a bad wiring connection whereas if the trany code only shows up only when the vehicle is cold, it shows a temperature sensor in the trany is not working.
4.) Do the basic visual inspection of the transmission
After you have done the above procedures, it is now time to check your transmission. The best way to do this is to have the trany steam washed in your local car wash station so you can have a good look of the trany components. If you want to see the solenoids, wirings, module, governor, linkages of the trany, what a better way to do it when the trany is clean. On most vehicles with front wheel drive system, it is just a matter of raising your engine hood in order to see the trany. You can give it a good spray of engine shampoo and steam washed it after the shampoo is soaked for a few minutes. Just remember to give a good spray of WD-40 on all electrical wiring connections especially the ignition engine parts (if you don't do this, the engine might not start after you washed it).
Once it is dried and clean, it will be easy for you to check the trany wirings and trany components that you wanted to inspect. Examples: you can check the wirings for tightness in the plug-ins, corrosions and routing. Some wires might be bare and rubbing on metal which can cause a short. In other case, a loosely held wiring harness touching a hot exhaust manifold at the back of the cylinder head can cause the same shorting problems. If you have a trany intermittent light flashing on and off, this is the best time to splice open the wiring harness close to the trany solenoids and check them for discoloration or shorting out if the harness is known to be soaked in oil or water.
5.) Don't forget your trany code and its description
Once you have the trany code scanned, it can lead you direct to the problem. Example: if the code says defective shift solenoid, you can check that solenoid by doing some DVOM testing. You can measure the resistance of the shift solenoid coil and compare it to the standard specs. You can also power up the solenoid itself manually and determine if you can hear it working ( a clicking sound normally indicates this). If you can connect a jumper wire from the battery terminals to the solenoid coils, you should be able to do this. All you need is a trany wiring diagram so you can determine the colors and location of the solenoid wires.
A lot of times, most of your trany fault code problems can be solved by using the above tactics without going to a garage for an expensive repairs. Note also that when you go to the garage in case you cannot repair the problem, you are in better position to give relevant information to the garage mechanic. And when you do this, it helps cut cost because the mechanic knows that you have a basic understanding how your trany works and that will prevent rip offs.