Solving Transmission Problems

Diagnosing Automatic Transmission Problems, Preliminary Checks

You might be somewhat limited when it comes to diagnosing automatic transmission problems. In addition to the special tools you need to repair them properly, there are also special tools for diagnosis. One of the main tools is an automatic transmission pressure gauge.

This is one of the main diagnostic tools for automatic transmission problems. If you do have one of these tools, great. You’ll also need the service manual, which can tell you where to check the pressures as well as what those pressures should be. There are several pressure ports on the transmission. Knowing which ones to check and what pressure you’re supposed to see is a big part of automatic transmission diagnosis. If you don’t have access to an automatic transmission pressure gauge set, or the service manual information, here are a few general tips to get you started.

The first thing is to be able to differentiate between an automatic transmission problem and an engine performance problem. Much of this is covered in the Engine Performance Article, but I’ll go over it again here briefly. One of the easiest ways to find out if it’s an engine performance issue or an automatic transmission problem is to do a power braking test. In this test, you put the vehicle in drive or reverse, set the parking brake, hold your foot on the vehicle brake, and floor the gas pedal. The RPMs should top out somewhere in the 1500 to 3500 RPM range and hold there. If it’s an engine performance problem, it will likely show up here, as you are putting the engine under an extreme load. You don’t want to do the test for too long for that very reason, as you could overheat the engine. You’re just performing a check here, you’re not trying to blow up your engine.

Another test you can try if you’re having a shifting problem is to shift the transmission manually if possible. Some automatics have the ability to move the shift lever through the gears manually one at a time. Some only allow you to shift from second, but that’s better than nothing. The point of this test is to see if the transmission acts normally when you shift it yourself. If it does, this might indicate a problem with some of the automatic transmission controls and not the actual gears themselves.

This might or might not work on transmissions that have the upshift/downshift or sport mode feature. With these transmissions, you can take manual control of how the transmission shifts; they’re mostly referred to as sport shift or something like that. This is basically a manual override, but it still uses the same electronics to shift the transmission as it uses in automatic mode. What I’m talking about is physically moving the shifter from gear to gear, not just using paddle shifters or a special mode for the shift lever. You might get results shifting with sport shift, but as I stated, these modes use the same electronics to shift the transmission as the automatic mode does and you’re not moving the manual valve in the transmission that mechanically selects a gear. Because of this, you won’t get the same result.

Checking Fluid Level and Condition

Check the fluid level and condition. The lifeblood of the automatic transmission is the fluid. If the fluid is low or it has a bunch of air bubbles in it, the transmission won’t function properly. Some people like to sniff the fluid to check its condition. I was advised some time ago that this is not a good practice and can be harmful to your health. You don’t need to sniff the fluid to check its condition; usually checking the color is enough, as well as looking for air bubbles like I mentioned. If you pull a dip stick out and there is a rank smell coming from the transmission, you really don’t need to sniff the dip stick to confirm it. Go ahead, get it out of your system. I feel like I handed you a loaded gun with that last sentence.

The darker the color, the more contaminants the fluid contains. Healthy transmission fluid should be a nice pink or red color. The darker it gets, the more contaminated it could be. I realize that there are some performance fluids out there that are darker than normal transmission fluid. These fluids still have a nice color even though it’s darker than what would be considered normal. What you’re looking for is more of a brownish or grey color to the fluid. This could indicate wear within the transmission itself.

I could go on about this for some time, but I think you get the picture. If the fluid is low, top it off and then recheck for the problem you’re having. If it goes away, find out why the fluid was low and repair it.

One note on this: On most transmissions, the two dots on the stick are the operating range. As long as you’re between these two dots, you’re good. If you go to fill the transmission, avoid overfilling. It’s much easier to add transmission fluid than it is to remove just a little. You might have to wait for a while between fillings in order to get a proper reading on the stick. It’s been my experience that the space between the upper and lower levels is only half a quart; keep this in mind when adding fluid. Avoid overfilling, as that can be just as damaging as not enough fluid.

Also, most transmissions are checked with the engine running and in park on a level surface. Consult your owner’s manual for specifics on how to check and top off your transmission fluid, as well as what type of fluid to use. You might find that on some transmissions you don’t have a dipstick to check the level with. These transmissions often require that the fluid be checked from service ports on the transmission. You’ll need to know where these are and the procedure for checking the fluid on these transmissions. Also know that the vehicle needs to be level when checking transmission fluid; if not, you’ll get a false reading. This goes for both transmissions with a dipstick and those with service ports.

Notes on Honda Automatic Transmissions

I single Hondas out here because I answer questions about this all the time. One of the main things to remember when checking Honda automatic transmission fluid is to make sure the engine is off when you do your check. If not, you won’t get a proper reading, and you could damage the transmission or the dip stick. It sounds strange, but I have seen it, more than once in fact. So make sure the engine is off and the vehicle is level when checking Honda automatic transmission fluid.

The other thing to remember about Honda automatics is that you need to use Honda automatic transmission fluid in a Honda transmission. If you use other automatic transmission fluids, the transmission might not shift the same and could have problems as a result.

Another thing to note about Honda automatic transmissions is that they don’t have replaceable filters. They do have filters, but they are internal and the only way to change them is to open the transmission case. Honda transmission filters are considered lifetime filters and do not have a service interval as a result. All you do with a Honda transmission is drain out the old fluid, clean the drain plug magnet and install about three quarts of new Honda fluid. Do this about every 30K and you shouldn’t have a problem with your transmission. Stray from this procedure and you might end up with issues.

One final note on Honda/Acura transmissions concerns the V6 transmissions from ’99 to ’03.  I’ll be honest; these transmissions had a very high failure rate. It doesn’t matter how you maintain them, it seems they are doomed to fail. If you’re considering one of these vehicles, have it checked out to see if the transmission had been replaced in the past, and even then be skeptical. I was putting in two and sometimes three of these transmissions a day for a while. That should tell you something about their reliability. When Hondas have a transmission problem, they often flash the D4 light on the dash. You can sometimes pull the codes with primitive methods; here’s a video on the procedure. This website contains a listing of the code meanings.

Here’s a video you might find helpful if you plan on changing the transmission fluid in your Honda.

Checking for Automatic Transmission Codes

Another step in your diagnosis is to check for codes. You do this in the same way you would check for engine codes. There are specific codes for automatic transmissions, but they are specific to manufacturer. This means that you might need a special scanner, and also the service information for your vehicle, to interpret these codes. Just about every late-model transmission is electronically controlled. This means that if you have an electrical failure, your transmission won’t shift correctly. Pulling the codes is a good way to find out if this is the case. If you have a shifting problem and you don’t have any codes, check the fluid level and condition. If it’s good, then it might be time to consult a professional.

Make sure to always take your car to a tire shop you can trust.

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