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Transmission Diagnostic Cost: Everything You Need to Know

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The only way for a mechanic to actually repair something that's gone wrong in your vehicle is to first know what's actually gone wrong in your vehicle. In many cases that means performing a general diagnostic. If you're having issues with your transmission in order to get to the root of the problem then a mechanic will have to do a transmission diagnostic on your vehicle to figure out what's gone wrong so that they have a better idea of exactly what to do to fix the problem. In many cases you can get a transmission diagnostic performed by a mechanic for between $100 and $150. 

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If you want to know how much a dealership charges for a transmission diagnostic you may end up paying a little bit more. Many dealers have a flat rate fee for diagnostic work that starts anywhere from $115 up to $200.


What is a Transmission Diagnostic?


A transmission diagnostic is essentially a routine through which a mechanic will observe your transmission and check over the individual components to determine which ones are working correctly and which ones perhaps need to have some repairs or replacements made.  Consider it the same as getting a checkup from your doctor. Just some routine tests and observation of your body to determine and your general health is where it should be yours if you are suffering from certain kinds of problems that are going to need to be fixed.


On older cars a transmission diagnostic is more of an in-depth process than it is on modern cars. It's also a lot less accurate. Because older cars, and by this we need one set were around before much of your car’s operational systems became computerized, when a problem arose with transmission it had to be diagnosed based on little more than a mechanic's own expertise and observational skills. They would listen to  the sounds that your transmission made, pop the hood and take a look at the moving parts that they could see from where they were and really just use a lot of guesswork to figure out what might be going on.


Modern transmission diagnostics do not have to rely on so much guesswork to get the job done. In fact, thanks to powertrain control modules and engine control units in your car that are the computerized brain of your electronic systems you can diagnose the problem very accurately if you have the correct tools to do so.


How a Mechanic Diagnoses Your Transmission Problems


If you have ever had to go to a mechanic to have a problem diagnosed because you weren't sure exactly what was going wrong you may have noticed that they plugged in a small computer device to your car. This device is called an on-board diagnostic scanner, or OBD2 scanner. These are often used when you have a check engine light for instance, and you aren't sure what it means. You take the car to the mechanic, they plug in their OBD2 scanner, and the scanner interfaces with your car's internal computer system to narrow down the check engine light to the precise problem that is referring to you.


The OBD2 scanner will give the mechanic a diagnostic code. Off and it will appear as something like p0622. The scanner will coincide with a specific problem. For instance, you may get a problem code that indicates your camshaft position sensor has failed. Or maybe that your exhaust manifold has failed in some way. Whatever the case, it takes it from a very general problem, in this case check engine, and narrows it down to a much more specific component. That makes fixing the problem so much easier because you don't need to check 100 different places.


When it comes to diagnosing transmission, the problem is much the same. If the mechanic plugs in the OBD2 scanner and they're going to get a code that tells them something like you have a problem with your gear ratio going from first gear to second gear. 


What Happens During a Transmission Diagnostic?


After the mechanic has attached the OBD2 scanner to your car and gotten a specific error code it will direct them to the exact area of the transmission that has a problem. At this point they can focus their attention on figuring out why there is a problem at that particular place either transmission. You'll likely have to do a test drive while sensor data gets monitored and information is taken from your car's engine control unit. This is necessary to determine if you genuinely do have a problem with the transmission in specific, or if there's a problem with the sensors, the engine control unit, and so on sending faulty signals.


If it's a problem with the electronics sending faulty signals and you may need to replace some sensors, or the engine control unit, or something like that. If it's genuinely a transmission problem, then the technicians can then focus in on exactly what is wrong with your transmission to get it repaired and working as normal again for.


What Gets Checked During the Transmission Diagnosis?


As we said the main part of a transmission diagnosis will involve the mechanic attaching an OBD2 scanner to your car to determine the nature of the problem you're experiencing. However, many mechanics and dealerships will perform a multi-point inspection if you bring your vehicle in for a transmission diagnostic. In these cases, you could expect a number of different aspects of your vehicle to be tested.


  • An OBD2 scanner evaluation
  • A check of your transmission fluid levels
  • Initial transmission engagement
  • Upshift timing
  • Downshift timing
  • Upshift quality
  • Downshift quality
  • Neutral performance
  • Reverse performance
  • 4X4 performance
  • Parking
  • Vibrations
  • Passing gear
  • Torque converter clutch engagement
  • Shift linkage and cables
  • Vacuum connections
  • Harness connections
  • Ground
  • Mounts
  • U-joints
  • Pan gasket
  • Fluid retention
  • Axle and shafts


It's also possible that other aspects of the transmission will be tested as well depending on what kind of service you ask for and how thorough the mechanic or dealership you've taken your vehicle tends to be


How Long Does a Transmission Diagnostic Take?


How long a transmission diagnosis takes really depends on the level of service that you are paying for and expecting to get from your mechanic. The actual diagnosis itself may only take a couple of hours to perform. Perhaps as little as one hour. Even though the diagnosis may be that fast, it's also possible that the mechanic will ask you to come back within half a day, or even a full 24 hours later. The reason for this is that, as we've seen with the list of inspection items, they may have a lot more that they want to do then just a bare-bones transmission diagnostic.


The main thing to consider here is whether or not you're just getting a diagnosis or you're getting repairs done. Obviously if there is a problem you would expect that the mechanic is going to fix it as well, so you may leave instructions to do a diagnosis and repair. It all depends on what you and your mechanic have worked out ahead of time in regard to how much they're going to test, and what they're going to do about anything we discover. As we said though, as a rule of thumb you can expect a  transmission diagnostic to be anywhere between 1 hour and 4 hours in length. 


What Are the Signs of a Bad Transmission?


Obviously, you're not going to take your vehicle in to get a transmission diagnostic until something happens that makes you think you need it. There are some signs and symptoms that your transmission is going bad that you can be on the lookout for to let you know you're in need of a diagnostic and potentially separate repairs.


Burning Smell


When your transmission starts to fail it may overheat. Old transmission fluid that has become contaminated and is wearing out will produce an unpleasant burning odour. This is a definite sign that you need to get to a mechanic right away.




Transmissions will often make some unusual sounds when they begin to fail. You may hear grinding or squealing sounds as you try to shift gears or even when you're just in neutral. Sometimes this means you just need to have your transmission fluid replaced, but it could also be indicative of a bigger problem that you need to have addressed.


If you experience a kind of humming sound or clunking sound this may also indicate a problem with your transmission that needs to be addressed as soon as possible. 


Trouble Switching Gears


A definite sign that there's a problem with your transmission is if you are having issues actually switching between different gears. When you're running low on transmission fluid this can be one of the causes, but there could be a mechanical cause as well if you find that your car simply will not switch from one year to another or it's a struggle to do so.


Slipping Gears 


Similar to problems with switching gears, slipping gears is what happens when you change gears even though you didn't intend to. When your transmission slips from a higher gear into a lower gear it's a clear sign that you need to get to a mechanic quickly to have it looked at. This could potentially be very dangerous if it happens while you're driving on the highway and suddenly you drive gear and end up lowering speed unintentionally.


Leaking Transmission Fluid


A clear sign that you have a problem with your transmission is if the transmission fluid is visibly leaking out. Transmission fluid should be red when it's clean, but it may take on a dark brown and muddy quality when it's old or contaminated. Regardless of what colour it is, if you can see at least you know then clearly you have a leak somewhere in the system which is going to cause your transmission to overheat and fail much sooner than it should. 




If your vehicle begins to shake and you experience some grinding as you shift through gears, that's a good sign as well that there's a problem with your transmission that will need to be looked at. 


Check Engine Light


Even though this is a very vague warning which could indicate any one of hundreds of problems, if there is an issue with your transmission it  very likely will show up on your dashboard in the form of the check engine light. This is exactly why you would get a diagnostic done because the check engine light really doesn't indicate the nature of the problem, so a diagnostic tool needs to be used to help you narrow the problem down.


 Can I Do My Own Transmission Diagnostic?


This is a bit of a yes and no situation. You can head to Amazon.com right now and buy an OBD2 scanner that you could use yourself for much cheaper than what a diagnostic will cost you at and I can while a diagnostic runs from $100 to $400 as we said, you can get an OBD2 scanner for perhaps $30. This will allow you to run a scan and provide you with the same code that a mechanic would use to help further fix your vehicle.


The problem here is that a mechanic may do a much more extensive diagnostic as we've shown with all the tests that they could run and the systems they could inspect. Additionally, if you are doing the scan yourself and you get an error code, a mechanic might still want to do their own diagnostic digital to confirm the problem afterwards. Unless you plan to do the repairs yourself after doing the diagnostic, it may not help that much to do it on your own.


The Bottom Line


Because the transmission in your vehicle is such a complicated piece of technology which includes many hundreds of different parts you can see the necessity of having a proper diagnostic to help you figure out what's wrong. The cost of a total transmission replacement can be many thousands of dollars, so it's definitely in your best interest to narrow down any potential problems and get them fixed as quickly and cheaply as possible before things get too bad. 

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