Why You Might Want to Reprogram Your PCM

Why You Might Want to Reprogram Your PCM

Computers control the modern world. You probably use one for work, they are essential for global banking, and they might even control your refrigerator. Your car is no different, and just like your cellphone, the computer in your car may need updating.

In this article, we’re going to talk about your car’s brain, aka the powertrain control module. The PCM is in charge of making sure your engine and transmission are running as efficiently as possible. To start, we’ll talk about what the PCM is, why you might want to reprogram it, and what it takes to perform that operation.

What Is a PCM?

When cars first started using computers to manage the engine, there was a single ECM, or engine control module. You will sometimes see ECU, or engine control unit, instead of ECM. It’s the same device; some manufacturers simply call it an ECU instead of an ECM.

As cars became more complex, they needed a computer to manage the transmission as well. These TCMs, or transmission control modules, monitor the speed of the transmission and work to best utilize your engine’s power band. We actually have a quick write-up on TCMs here.

Modern cars have a computer that is both a TCM and an ECM. Since the engine and the transmission are the primary components of a car’s powertrain, we call this computer the powertrain control module, aka the PCM.

What the PCM Manages

At its core, the PCM is in charge of regulating and monitoring the engine and transmission. Modern cars have a ton of electronics and sensors that all contribute to the efficiency of the motor. Even the basic functions, like when the spark plugs fire or how fast you can go, are functions of the computer; your modern car literally can not run without the PCM.

Here are some of the biggest functions that a PCM must perform.

  • Manage the air to fuel ratio
  • Control the ignition timing
  • Direct the fuel sending unit and related systems
  • Relay information to the gauge cluster
  • Log and detect faults
  • Set the transmission shift points

Sensors

In addition to managing the systems, the PCM has tons of sensors that constantly monitor the engine. It’s always collecting data and adjusting things to keep your car running smoothly. Common sensors include the mass airflow sensor, the manifold absolute pressure sensor, the speed sensor, the throttle position sensor, and the temperature sensor.

These sensors can fail and send false data to the PCM. That’s one of the most common reasons an engine will run poorly. In fact, checking the air sensor is often step number one when diagnosing fuel mixture issues or engine start issues. When a sensor sends bad data, the PCM tries to compensate for the bad data by bringing all the other systems into tolerance, which usually leads to terrible run conditions.

OBD2 and the PCM

Ever since it became law in 1996, cars have been equipped with an onboard diagnostic system, or OBD for short. The current standard is the second generation of diagnostics, which is why it’s called OBD2. The onboard diagnostic system constantly monitors the engine’s health and creates fault codes if something goes wrong. You can then read the fault codes with a scanner like one of the ones we recommend here, and you will be able to find out what went wrong.

The codes and troubleshooting software, so to speak, are all contained inside the memory of the PCM. When a fault code is generated, it’s stored in the PCM, and the PCM will tell your check engine light to illuminate.

That’s one of the benefits to the complexities of modern engines. They can be more frustrating to work on and understand, but with OBD2 and modern PCMs, they can often diagnose themselves. They can also compensate for almost any change instantly, which is great if there’s a problem because the computer will work hard to protect your engine from further damage.

Reasons to Reprogram a PCM

the PCM in an engine bay

Reprogramming a PCM is not a common thing to do. It’s fairly involved, and the average home mechanic won’t ever have a need to perform the task. However, there are three main reasons you might want to have your PCM reprogrammed.

Before we begin, you might see the term “flashing.” Flashing is an older term for reprogramming. Older ECMs had hard-coded memory that needed to be “re-flashed.” Think of it as having to install a new version of windows vs. just installing a program. Older modules needed a brand new fresh install every time. Modern modules can just have apps installed onto them.

General Updates

Modern car computers sometimes need updates just like your home computer. Newer cars can sometimes get updates over WiFi. Older cars from the 2000s sometimes used CDs or USB drives to update the PCM. You can often find updates for purchase on eBay and other used parts stores, and it doesn’t take much time to update the computer yourself.

However, sometimes a car needs to be updated using specialized computers running proprietary software. Those updates need to be installed by your car’s dealership.

PCM Is Damaged

If you have to replace the PCM because the previous PCM is damaged, you will probably need to program the new PCM. The same PCM is often used on many different models, with only the programming changed between them. It’s very common to buy a new PCM from a dealer and then have to take the car in to have it programmed correctly.

You may want to have a PCM programmed even if you get a used PCM or a model-specific module. A shop will have the most up-to-date programming, and they will have tools to program it quickly.

Tuning

The final reason to program a PCM is to make your car better at specific tasks. When they come from a factory, a car is often programmed to balance comfort, economy, and power. By adjusting the fuel ratio and the timing, you can tune a car for more power or better economy.

Tuner culture, as made famous by the Fast and the Furious movie franchise, exists because it’s possible to reprogram the PCM. Most of the time, this isn’t something that your local dealership will do. Dyno shops, custom engine builders, and home performance enthusiasts have special tools that interface with the PCM and allow them to freely change parameters.

PCM Programming Alternatives

There are devices on the market that offer an alternative to reprogramming a PCM; most are performance-oriented.

Beware of Scams

The biggest thing to know before looking at alternatives is that there are a lot of scams out there. Generally, if it seems too good to be true or seems like it shouldn’t work, it won’t work.

Be especially wary of any product that doesn’t use an OBD2 port or USB port to interface with the car. A host of products claim to update the programming via the 12v charging port on your dash. The 12v plug does not interact with your PCM; these devices are scams.

Access Ports

Companies like Cobb offer devices that can tune a car in real-time. They even offer a variety of pre-programmed settings that make it incredibly easy to program your PCM.

The device itself is simply an interface that creates a place to plug a computer into your PCM. You cut some of the wires going into the PCM, or buy an adapter, and install the port between the existing system and the PCM. Some cars can use Bluetooth or WiFi instead. That is somewhat rare, though.

Stand Alone ECUs

For older cars that don’t have a PCM, or for some newer cars that don’t take well to a tune, you can buy stand-alone PCMs that are not vehicle specific. Then you can buy programs or write your own program, to manage any engine in any way you want. They are very common in race cars since the engines are often custom-built and benefit from routinely being fine-tuned.

There are also companies like MegaSquirt that build PCMs specifically for some models. That makes it very easy to install a new PCM and tune your car to your liking very quickly.

How Is a PCM Reprogrammed?

There are two main ways to reprogram a PCM. The easiest way, and the way that most people will choose, is to pay a shop to do it. The tools required are highly specialized, and if you install the wrong programming, you can ruin your car.However, there are ways to do it yourself, and we can give you a short walkthrough to get you started if you are interested in tackling that process.

Going to a Shop

Many mechanics can program your PCM; many do not because of the knowledge required. Usually, you’ll be taking it to a performance shop or a dealer.

Dyno or Performance Shop

If you are customizing your car’s performance, you will likely need to take your car to a dyno shop. A dynamometer, which is a big machine that you drive your car onto, measures the amount of power your vehicle is making. That way, the shop can make small changes to your programming and measure for power increases.

It usually costs about $600 for a dyno tune, but it can be $1,000 or more in some areas. Even if you aren’t setting out to program your PCM, people who care about performance should visit a dyno shop. The operators are usually highly knowledgeable and love to help people make more power.

Dealership

If you need a specific tune or program for your vehicle, often a dealership is the only place to get it. The cost will vary greatly depending on what you need and how new your car is.

Often, updates are free because they are produced by the manufacturer to solve known issues. They will be covered under warranty or recall. Newly purchased PCMs through the dealer will also usually be programmed for free.

It may cost a bit to have them program an aftermarket or used PCM, though. It is usually far cheaper to have them program a PCM than replace one, so it’s still a good option if you are repairing your car.

Doing It Yourself

It’s difficult to give you much guidance on doing it yourself because it’s entirely dependent on what you need to do and what car you drive. Some cars are very easy to program yourself, and there are plenty of guides online, like this video showing a home reprogramming of a Mazda 6.

Other cars will require extensive modifications and the installation of an access port like the ones we discussed up above.

We do have some general tips for you that can help get you decide if home reprogramming is right for you.

  • Have a backup plan. If you are reprogramming a car’s computer, make sure to save a copy of the original program. You might even consider buying another used PCM just in case.
  • Research different tunes and read what other people have done successfully. You can save a lot of time if someone else has already created a program for your car that is proven to work.
  • Beware of scams. We said it above, but it needs repeating. There are a lot of “this will add 15HP!” devices that are nothing more than an LED and a waste of money.
  • There are vehicle and model specific flash reprogrammers that are often cheaper than universal connections. However, using these devices will void your warranty, and they don’t offer much customization.
  • You don’t need a very powerful computer to tune a car. In fact, a cheaper, older laptop is often a better tool than an expensive stand-alone tuner. The most difficult item to source is the interface cable.

Program Peak Efficiency

Reprogramming your PCM can be an excellent way to make your car more in tune with your demands or to fix simple issues. It can also be a new, rewarding hobby if you are inclined to buy the right cables and programs. Just be sure to keep a backup, and don’t be afraid to ask for help.