Transmission Light Comes On? Here’s Why And How To Fix

Your car's transmission light suddenly comes on and you're not sure why? Don't fret. Here's exactly what you need to do in order to solve the issue.

You’re driving along one day, minding your own business, when the car’s transmission light comes on. Okay – what now?

You must go to a mechanic even if you don’t notice any other symptoms. I suggest going straight to a transmission specialist to avoid potential markup fees.

This guide explains the transmission warning light and what you need to do next.

Key Takeaways

  • You need help from a trusted transmission rebuild shop.
  • A blinking transmission light means there’s immediate danger. Pull over and call a flatbed tow truck.
  • A steady transmission light, illuminated constantly, still means something’s wrong. You can probably drive to a shop.
  • Transmission repairs (rebuilds) or replacements are almost always four figures. Both are good choices with essentially the same result. Go for the cheapest reliable option.
  • Transmission replacements are often cheaper for more common cars.
  • The cost of transmission repairs or replacements varies significantly. However, you can expect to pay four figures – between $1,000 and $4,000 in most cases.

Table of ContentsShow

Why Is My Transmission Warning Light On?

New modern car interior

I completely understand your question. You want a more direct answer so you can decide how to proceed.

Unfortunately, that’s not quite how this is going to work.

Your transmission light is on because there’s something (and it could be anything!) wrong with the transmission.

A sensor has noted an anomaly (one-off or consistent). This has caused a code to be stored in the ECU’s TCM (transmission control module). In turn, this causes the light to illuminate.

Issues could also arise from related systems or sensors.

Why Is My Transmission Light Blinking?

A blinking transmission light represents immediate danger. As in, you must pull over to the side of the road and stop your engine.

In contrast, a constant light (one that’s on constantly) means there’s a problem that needs attention, but it’s not an immediate threat.

To say it differently, if you notice a blinking transmission caution light, it suggests that you should be transported to the transmission store on a flatbed tow truck. In case the light remains constant, it could be acceptable to drive there.

Despite this, use common sense. Be ready to pull over and ring for help if the situation calls for it.

What Cars Have A Transmission Warning Light?

Automatic Transmission (Park)

Transmission warning lights are (in general) only found on vehicles with automatic transmissions.

Cars with a manual (‘standard’) gearbox don’t have a warning light. You need to detect any shifting issues yourself.

You may or may not find a transmission warning light with electric cars. It depends on how the vehicle was designed!

The appearance of the transmission warning light varies between manufacturers.

If you need clarification on what a particular dashboard warning light means, check your owner’s manual or do a quick Google search. You’ll find the answer soon enough!

How Does A Car’s Transmission Work?

I’ve used this video from Lesics (on YouTube) in a few other articles, and with good reason. It’s the best simple explanation I can find.

I’ll sum it up for you as briefly as possible: they’re complicated. So, so, so complicated.

In fact, I think most mechanics would agree with me when I say engine rebuilds are easier!

A system of clutches, planetary gears, and ring gears is linked with input and output shafts.

Changing the active and passive gears produces diverse ratios between the speed of the engine (input) and the speed of the wheels (output).

Still with me? That’s all you need to know for now! The video I’ve attached above explains it in much more detail.

On top of this basic functional setup, they’re fitted with loads of different sensors. Electronics and hydraulics control the gear changes.

If necessary, these features combine to activate the transmission warning light. Thus, you know there’s a problem that needs your immediate attention.

The light could indicate something wrong with the transmission itself. It might also represent an issue with related components or sensors.

Transmission Light Comes On: Accompanying Symptoms

automobile transmission

In this section, I’ll run through the indications you might expect to see alongside a transmission warning light.

This isn’t an exhaustive list, and whether you notice any or not, you must still go to a mechanic.

No Extra Symptoms

You might not notice anything else at all.

Something has still caused the light to come on. This needs to be investigated using an advanced OBD code reader found at a professional shop.

Rough Shifting

Clunky, heavy, hesitant, or noisy gear changes are the most clear-cut sign of a breaking transmission.

This includes changing up or down while accelerating, but also between Drive, Reverse, and Park when stationary.

Dirty Or Low Transmission Fluid

Car mechanic drain automatic transmission fluid

Check your ATF using the dipstick under the hood. Consult your owner’s manual if you need help determining which one this is.

The dipstick should show a safe level of red transmission fluid.

Brown or black fluid – or if it has particulate matter in it – means it’s old and needs a flush. If the level is low, you might have a leak.

Vibrations, Clunks, And Other Discouraging Sounds

As the main driver of your car, you’ll know what it usually sounds like. If anything seems different with the noise it makes, it could be the transmission.

Other Dashboard Warning Lights

A transmission light could be accompanied by others, such as the Check Engine icon.

Limp Mode

Limp Mode is when your car limits its top speed and acceleration. It’s putting itself in a worst-case scenario to protect its powertrain from further damage.

Limp Mode might be annoying, but you’d be in an even worse scenario without it.

Transmission Light On In Car: Causes

Again, I’m not going to spend too long running through the causes of a transmission warning light. The possibilities are virtually endless.

Here are a few of the most common:

  • Old, worn-out transmission fluid (ATF)
  • Leaks (usually at seals)
  • Slipping gears (often caused by broken teeth or heavy impacts)
  • Worn-out torque converter
  • Breaking shift solenoids
  • Slipping clutch(es)

How Do You Fix A Transmission When The Light Is On?

If your car’s transmission light has come on, you should visit an expert.

They’ll use OBD code readers and general mechanical tests to identify the problem.

If you’re lucky, it’ll be something simple and outside of the main transmission housing. Otherwise, you’ll need an expensive rebuild or replacement.

Visiting a store you have faith in is top guidance from me. Then, you can count on the expert’s recommendations more.

Should You Get A Replacement Transmission Instead Of A Rebuild?

car transmission repair

If you’re given a quote for a rebuild, it’s worth checking through reliable online stores for refurbished transmissions. Make sure they fit your specific make and model.

Add around $800 to this price to account for the shop’s labor rate. (This is a general estimate – they might charge much more or less.)

Now, which is cheaper?

Remember that you have more quality assurance from a rebuilt transmission. You should also have a more straightforward warranty option.

Put all this information together to come up with the best way to move forward.

Can You Repair A Transmission At Home?

No.

You don’t have a hope of repairing a transmission at home. Even a fully qualified and experienced mechanic wouldn’t attempt it.

An automatic transmission contains literally thousands of intricate and fiddly parts. Disassembling it requires expert knowledge, intense focus, and a keen eye for detail.

In other words, putting a transmission together is like completing a 1,000-piece jigsaw puzzle without the picture. And if you get any parts wrong, it breaks, potentially damaging other components.

If you’re looking for more reasons to avoid repairing your transmission at home, I have loads for you:

  • You need to raise the car a significant amount to drop the transmission out.
  • If you get stuck, you can’t drive the car, and it’ll be tricky to tow it anywhere.
  • You need a reliable trolley jack to hold the heavy transmission up.
  • If it falls off the jack, it could injure you or damage itself even further.
  • ATF (automatic transmission fluid) or gearbox oil absolutely stinks. You’ll smell it for weeks if it gets on your skin or in your hair or clothes. Think BO, but much worse.

I could continue, but I think you get the point!

Conclusion: What To Do If The Transmission Light Is On

If your transmission light is on, there is almost certainly a problem with the transmission. That probably doesn’t come as too much of a surprise!

Yes, the issue might lie with a sensor or electrical part rather than a mechanical component. But so what? These still need fixing! When they don’t work, the transmission is under extra strain and eventually breaks anyway.

Go straight to a transmission shop. You could opt for a regular mechanic, but they’ll almost certainly outsource the job to a specialist.

Going to the experts directly means you should save on any markup fees you’d otherwise be charged.

Finally, please let me reiterate the following with added gusto. Do not work on your own transmission.

YouTube tutorials are not the way forward, I’m afraid!

This will be a four-figure repair – there’s no way around that. Don’t make it worse by attempting to fix your transmission yourself!

Ultimately, you might have to decide if it’s worth spending this much on a new transmission.

That’s about all I’ve got for you in this guide! As always, drive safe, and if your transmission light is on? Go straight to a shop!

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Benjamin Kitchen

Ben is an IMI-qualified light vehicle technician from England with experience in a fast-fit garage. He aims to help drivers worldwide with common automotive problems. You’ll often find him working with his 1.2 Vauxhall Corsa. It may have a tiny engine, but in eight years it's never once let him down!