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AT light on Mazda – Causes, how to fix, and cost?

Is your Mazda’s AT light switched on and you’re not sure what it’s all about? Are you hearing weird noises while driving and feeling a bit concerned?

Bad news, fix it asap, or you may pay more money for the transmission in the near future.

Don’t panic! I’m already here to help you with:

  • What the AT light means
  • How you can diagnose the issue yourself
  • How much it’ll cost you. 

Let’s get into it!

What does AT light mean?

An AT light is found in all Mazda vehicles and stands for “Automatic Transaxle”. Having an AT warning light on could mean a few things like low transmission fluid, dark color transmission fluid, or something (seriously) wrong with the transmission system.

definition and common causes for AT light on Mazda

If your Mazda vehicle has an illuminated AT light, first, you need to check the transmission fluid for its:

  1. Level
  2. Color

Low transmission fluid – Most common cause for AT light

Transmission fluid is responsible for lubricating the transmission. It also keeps the transmission system cool, ensuring the longevity of the vehicle.

Low transmission fluid is the leading cause of the illuminated AT light in your Mazda car. And that’s the first thing you need to check.

Signs to look for 

To help you diagnose your Mazda’s AT light problem, here are a few symptoms of low transmission fluid.

  1. Noises (whining, humming)
  2. Burning smell
  3. Slipping gears

How to fix

Just top up your vehicle with transmission fluid! Here’s how you can check and add the transmission fluid yourself!

However, watch out for leakages!

When you see a small puddle of reddish fluid (smell sweet or tart smell) underneath your car, that’s transmission leak!

To locate a leak, check the pan gasket and the bolts around it (and a few other things need to be inspected, but these two are the most common issues).

Loose bolts from an earlier transmission fluid change can cause leakages. Make sure to tighten the bolts on the pan gasket.

You may find that the bolts are tight. In that case, there might be a crack in the gasket that requires replacement.

Large cracks would require replacing the gasket. It’s actually quite easy to do, you totally can replace the pan gasket at home and save some money. Here’s how:

You can fix minor leaks in the gasket by using transmission stop leak fluid. It is a great solution to help seal up minor leaks in a transmission system. 

Bar's Leaks 1416
Bar's Leaks 1416 Super Transmission Fix
4.3
Simply pour the transmission stop leak fluid in the transmission and drive your vehicle as you would. It should take about 200 miles for the leak to stop.

How much does it cost?

Topping up your transmission fluid is inexpensive. Depending on the brand, you may be looking at around $20 – $50 per gallon of transmission fluid. Using transmission stop leak fluid for minor leaks is an additional $10 to $12.

Replacing gaskets is relatively cheap as well and will cost you $20 to $45. However, taking the vehicle to a mechanic to replace the gasket will cost upwards of $150.

Dark-color transmission fluid

If the transmission fluid is OK, the next thing you want to check is its color.

Following the instruction of the video above, you can also check for the transmission fluid color. There are 3 basic transmission fluid colors you’ll get:

Bright red (on the right of the picture): the fluid is good. The problems causing AT light must be something else.

Dark red (in the middle): you need to change the fluid.

Brown or black (on the left): at this point, something bad might already happen to your transmission system. A complete transmission flush is the first option (very risky, you should let a mechanic decide if your car needs that or not).

Replacing the oil filter is another common solution. But if it doesn’t stop the symptoms (very likely to happen when the fluid is completely black), you need to rebuild the whole transmission.

tranmission fluid color
The darker the fluid, the more money you’re gonna pay.

How much does it cost?

Transmission fluid colorSolutionsCost (labor included)
Dark redTransmission fluid change$80 - $250
BrownTransmission flush$100 - $200
BrownOil filter replacement$250 - $340
Brown, blackTransmission rebuild$1,200 - $5,000

Use OBD2 scan tool – Most effective option to turn AT light off

If there is no issue with transmission fluid, then you may have a bigger problem.

To diagnose the potential problems with your car, you can use an OBD2 scan tool. The device will tell you the fault code(s), which indicates the issues causing the AT light to illuminate.

Bad news, a cheap OBD2 scanner can only pull codes from the engine module. However, AT light comes from the transmission module, so you’ll need something a little more advanced (but not too much) than a 30 bucks code reader.

Bluedriver OBD scanner
Bluedriver - The most affordable option to turn off AT light on your Mazda
4.7
This device can access the transmission control module in all of Mazda vehicles and pull out the codes for you. Even if you cannot fix the problems, it’s always wise to bring your vehicle to a repair shop while knowing what’s truly wrong with your car. No more rip-off!

How to use OBD2 scan tools on Mazda

If you’re new to this thing, don’t worry, they’re very easy to use. Here’s how:

Common transmission fault codes causing AT light to come on

As a mechanic, whenever my “Mazda customers” have the AT light, I’m about 90% sure the list below is the case.

P0218: This refers to an overheated transmission due to low or dirty transmission fluid. However, if the transmission fluid is okay, there must be an issue with the temperature sensor.

P0613: This code tells you that there is a fault within the circuitry or the processor. A mechanic should fix this in no time. But it’s gonna be quite expensive.

P0614: This code indicates that the Engine Control Module (ECM) and Transmission Control Module (TCM) are incompatible with each other. It could perhaps be due to a recent change in any of these components resulting in incompatibility issues.

P0700: The most common cause for this code is a faulty TCM. Usually, when your car has this code, the check engine light will also come on.

P0706: Transmission range sensor communicates with the TCM letting it know the shifts of the gear lever. It also informs whether or not the gear is in neutral for the car to start. An issue with the transmission range sensor will bring up this code.

P0715: Your automatic transmission vehicle sends signals constantly with the TCM. It lets the processor know if the car is in the right gear. This code could be due to a corroded wire or may require input speed sensor replacement.

P0720: Your speedometer reads the speed using speed sensors. It lets the TCM know how fast the input shaft is moving. If you’re having a boggy speedometer, you may see this code. It’s time for an output speed sensor replacement.

P0729-P0736: This range of codes that report the same error: gear issues. The different code represents the gears having the problem. Usually, a simple transmission fluid top-up should fix this issue. However, if you still see these codes, there may be an issue with the torque converter. You may also see this code in junction with other codes. It can point to a corroded solenoid that helps regulate the torque converter clutch.

P0750-P0770: The TCM lets the transmission know when to shift gears by opening up solenoids. Doing so allows the transmission fluid to pass into the gear. You may see these codes in tandem with other P codes. It could be a solenoid failure. In such circumstances, your gear may not work.

How much does it cost?

Usually, one code may have different causes, and of course, different solutions. So, in the below table, it’s not 100% these solutions are musts; there may be others. But as a mechanic, I would say they are common fixes for these codes.

CodesCost (labor included)
P0218Replace transmission temperature sensor: $230 - $310
Replace faulty TCM: $500 - $900
P0613Replace faulty TCM: $500 - $900
P0614Replace faulty ECM: $900 - $2,000
Replace faulty TCM: $500 - $900
P0700Repair valve body: $320 - $900
Replace TCM: $500 - $900
Replace transmission: $1,200 - $5,000
Replace solenoid: $150 - $400 (Single unit)
P0706Replace transmission range sensor: $249 - $285
Replace PCM (Rare): $500 - $1,500
P0715Replace transmission speed sensor: $800 - $1,000
Replace transmission valve body: $400 - $850
Replace solenoids:$150 - $400 (Single unit)
P0720Replace transmission speed sensor: $800 - $1,000
Replace PCM: $500 - $1,500
P0729-P0736Replace valve body: $320 - $900
Replace TCM: $500 - $900
Replace transmission: $1,200 - $5,000
Replace solenoids: $150 - $400 (Single unit)
P0750-P0770Replace solenoids: $150 - $400 (Single unit)
Replace transmission fluid: $80 - $250

Conclusion

An illuminated AT light is a common issue among Mazda car owners. It requires proper diagnoses and fixes to avoid any further damage to your transmission system. Don’t ever ignore the AT light, or you’ll pay a much higher price.

Whether you have a lot of experience in car fixing or not, getting an OBD2 scanner is never a bad idea. It’ll save you thousands of dollars in the future.

And whatever the codes and symptoms you’re having, don’t forget to leave a comment below. I’ll try my best to help you out.

Peace!

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