One of the most vital components in your car is the Powertrain Control Module (PCM). The PCM has the responsibility to control the various parts and sensors of the engine.
It ensures the proper supply of coolant, engine oil, and air-fuel mixture. It turns ON the check engine light when any engine sensor creates a problem. This article deeply explains PCM function, symptoms, and causes.
What Is A PCM On A Car?
The power control module, shortened as PCM, is the computerized brain of your car system.
It controls the two main parts of the powertrain (engine and transmission) and many other car components. It takes action based on the information it receives from other sensors connected to it.
The PCM performs more than one hundred (100) functions at a time in a single vehicle. To carry out its functions, the PCM is connected to different sensors all through the vehicle to keep track of everything.
In other words, the PCM controls almost all car components. So if it fails or any of the sensors connected to it is faulty, then your car won’t work properly. This is because it won’t be able to carry out its functions with its brain.
The PCM is made of metals and comes in a box shape, with some wires connected from it to other car sensors.
It is often placed on your engine bay close to the fuse box or inside the vehicle close to the fuse box. In some vehicles, it is found underneath the front windshield.
So your PCM location depends on your car model and manufacturer. But in many vehicles, it is usually found in the engine bay. If it’s not there, it might be in your passenger’s cavity or under the passenger’s side dashboard covered by plastics.
While you research PCM, you may have come across the acronym ECM or ECU (Engine control unit or engine control module). Don’t get confused.
The ECM works together with another onboard computer called the TCU (Transmission control unit). While the ECM controls the engine, the TCU controls the transmission. But if the car is without an automatic transmission, then it utilizes only the ECU.
So in many modern vehicles with automatic transmission, instead of using two different onboard computers (ECU and TCU), the car uses the PCM. In other words, the PCM collectively does the work of the ECU and TCU.
Functions of the PCM
- Engine Management: It controls various engine functions such as fuel injection, ignition timing, air-fuel ratio, and emissions controls. This ensures optimal engine performance, fuel efficiency, and compliance with emission standards.
- Transmission Control: It manages gear shifts, transmission fluid pressure, and other aspects of the transmission system to ensure smooth and efficient operation.
- Diagnostics: The PCM monitors and diagnoses faults within the powertrain system. It stores diagnostic trouble codes (DTCs) which can be read using an OBD-II scanner to help in identifying issues.
- Adaptive Learning: The PCM can adapt to changing conditions and driving habits by adjusting various parameters for improved performance and efficiency over time.
PCM Location
A PCM is a metal box with some wires coming out of it. The position of the powertrain control module varies according to the vehicle model.
Mostly, the PCM is installed in the engine bay near the fuse box. In some models, you can also find it on the front windshield after removing a few covers.
If your vehicle’s PCM is not located in the engine bay, then it may be found inside the passenger compartment under some plastic coverings.
How Does a PCM Work?
The PCM receives data in the form of signals from the sensors and components connected to it and makes decisions based on them.
Some examples of the decisions it makes include how much fuel to inject into each cylinder, when to fire the spark plugs, and when to make the transmission shift to a different gear to deliver the best performance relative to its current condition.
When the flow of information between the PCM and other onboard computers and sensors is undisrupted, the vehicle performs smoothly and efficiently.
However, if something in the system fails, the PCM won’t know what to do. For example, if an oxygen sensor becomes faulty, the PCM won’t know how to adjust the air-fuel mixture going into the engine.
The check engine light can turn on and the engine might run roughly or have acceleration issues. If the PCM itself fails, the engine might not start at all.
How Does PCM Work in Hybrid and Electric Cars?
While typical PCMs manage internal combustion engines and automatic transmissions, their function in hybrid and electric vehicles reflects the greater complexity of these powertrains. Listed below are the PCM functions in EVs and Hybrids:
- Energy Flow Management: The PCM allows power splitting between the internal combustion engine (in hybrids) and electric motor, optimized for efficiency.
- Battery and Charging Coordination: It synchronizes with the Battery Management System (BMS) to control charging, discharging, and battery status.
- Motor Control: In electric vehicles, the PCM (or equivalent power control unit) controls the operation of electric motors.
- System Synchronization: The PCM synchronizes smooth communication between various ECUs, like inverter controllers, and drive-by-wire systems.
- Safety Monitoring: Continuously checks high-voltage system faults and activates safety modes to prevent accidents.
What Are The Symptoms Of A Bad PCM?
As smart as the PCM, it can act weird when something goes wrong. The following are some symptoms of a bad PCM.
#1. Illumination Of Check Engine Light.
One of the most common symptoms of a bad PCM is the display of check engine lights. The light could be on because of a powertrain-related problem. The problem making the light come on could also be wiring problems from sensors or anything else.
So, if light displays, make sure you have checked other faulty car components before concluding that the PCM is the cause. You can check for fault codes using any diagnostic tool.
#2. Poor Performance.
The PCM manages your car’s performance. So if it is not working properly, performance will be affected. The more the PCM gets bad, the more other issues will suffice, leading to poor operation.
But if it’s just one part of the PCM that is bad, poor performance may be experienced under specific conditions. For example, you may experience poor performance when idling or accelerating and not throughout the entire vehicle.
#3. Starting problems.
When your car PCM is faulty, you might find it difficult to start your car, especially in cold weather. In severe situations, your car won’t start at all.
Other issues such as a weak battery or failing starter can cause this. But if you notice the issue is from your PCM, please fix it. You can use any OBD11 scan tools to read trouble codes.
The scanner would also tell you how to go about it. Any further delay may lead to a total breakdown of the engine. And in the end, you will still buy the PCM, a new engine, and other parts affected by the faulty PCM. So which do you prefer?
#4. Increased Emission.
With a PCM in proper working condition, vehicle emissions are minimized with increased performance.
But when it doesn’t work as it should, emissions will be increased while performance decreases. However, you may not know you have an increased emission until you take your car out for an emission test.
#5. Poor Fuel Economy.
With a faulty PCM, you may start experiencing a reduced fuel economy that is consuming more fuel than usual. For example, you will accelerate more than usual if your turbo doesn’t generate enough boost because the PCM didn’t tell it what to do.
#6. Shifting Issues.
If you’re finding it difficult shifting your vehicles into gears, the PCM may likely be the cause. The PCM controls all that goes on in your engine and transmission. So issues with the powertrain might likely be traced to a bad PCM.
Gear shifting problems are serious issues that need to be rectified immediately. If not, you may have serious handling issues, making you lost control of your car. This can lead to an accident.
#7. Engine Stutters or Stalls.
A faulty PCM can make an engine stutter or stall. While it is advisable to have the PCM checked, it could be due to other reasons. For instance, engine stalling sometimes is caused by lousy ignition coils.
Causes of a bad PCM
There are several causes that lead to PCM failure. The following are the major causes of a bad powertrain control module:
- Manufacturing faults: Poor quality control during the manufacturing of the PCM may lead to its earlier failure. This issue may lead to the early failure of the internal parts.
- Wrong installation: Poor installation of the powertrain control module may badly affect its performance.
- Electrical problems: Various electric problems, such as a surge or spike, typically produced by a jump-starting, damaged wires, or faulty alternator, may damage your PCM.
- Environmental factors: Different environmental factors, such as excessive car vibration, moisture, extreme temperature, and pressure, may lead to a faulty powertrain control module.
- Software issues: Corrupted or outdated software may heavily affect the functionality of the PCM.
- Physical damage: Collisions, accidents, or many other types of physical damage may cause the failure of the powertrain control module.
- Water damage: A liquid such as water may penetrate the PCM, leading to a short circuit that can damage the internal parts.
- Age and wear: The internal parts of your powertrain control module wear out with time, which may reduce performance.
How to Test a PCM?
Before starting any job, it’s important to have the right tools for the task. Here’s what you’ll need to test a PCM:
- Flashlight
- Standard and Philips screwdriver
- OBD or OBD II code scanner (check with your car’s manufacturer on device compatibility)
- Multimeter
- A new PCM (if replacing)
Step 1: Visual Inspection.
Now, before you start doing any surgery on your car, the first thing to do is to check for rust or a disconnected wire. This isn’t the most common cause of a PCM failure, but it’s the easiest to identify.
Make sure that your PCM is connected to your battery, and that there’s no rust on the PCM itself or on the battery wiring. Reconnect any loose wires if necessary. If your PCM has experienced corrosion, you’ll have to skip to step 5 to see if it’s failed.
Step 2: Check Your Battery.
While you’re under the hood, use your multimeter to ensure that your battery has a full charge. It should read at least 12.6 volts with the engine off, or 13.7 volts with the engine running.
If it’s showing less than that, fully charge your battery and re-test. The reason this is important is that low voltage can cause certain sensors to fail, depriving your PCM of the input it needs to make correct adjustments.
Step 3: Code Scanning.
If your battery is fully charged and there’s no visible rust, your next step will be to plug an OBD or OBD II code scanner into your vehicle and see if the PCM is producing any OBD error codes.
This can be incredibly helpful in solving many mechanical and electrical problems since you can use these codes to narrow down which systems are causing the failure.
A codebook (or easy Google access) is a necessity here since you’ll need to learn what the codes mean in order to make head or tail of them.
We’ve written about several PCM-related error codes in the past, including the P0603 code, the U0100 code, the P0113 code, and the P0606 code. Obviously, this isn’t an exhaustive list, but it represents the most commonly-displayed error codes.
Step 4: Inspect Wiring and Sensors.
Hopefully, you had some success with the previous step, because this is where things can get tricky. You need to check the sensors that are connected to your PCM, as well as the wires that connect them.
If you’re seeing a PCM code – or two, or three – it can really help you narrow in on which sensors or wires are faulty.
Perform a visual inspection of these wires, as well as checking them with a multimeter. Don’t forget to check ground wires and connection points, either, since these are frequent causes of trouble.
Once you’ve replaced any failed components, reset your car’s codes, and drive for a while. Most likely, you’ll have solved the problem.
Step 5: Try a Replacement.
If all else fails, or to confirm some repairs, you may need to try running your vehicle with a replacement PCM. Ensure that the PCM is the correct version not just for your make and model, but for the same year as well.
If it turns out that your PCM was faulty, you’ll immediately notice an improvement in performance.
What to Consider When Looking for a New PCM?
Shopping for a new PCM can quickly become overwhelming because of the wide variety of options on the market. To help you choose the right one for your vehicle, here are some factors to consider when you’re in the market for a PCM replacement:
Application
Always check for fitment before buying a new PCM for your vehicle. Get a replacement that’s designed specifically for your vehicle’s year, make, and model to guarantee a perfect fit and hassle-free installation.
If you’re unsure, refer to your PCM’s replacement part number. It’s usually on the PCM itself or in your manufacturer’s catalog.
Condition
PCMs are available in new and remanufactured conditions. A new PCM is built from brand new components and materials, while a remanufactured PCM is an old but still perfectly usable module that underwent a thorough upgrade process that lets it compete with new parts.
If you’re on a budget, a remanufactured PCM will help you save money without downgrading your car’s performance.
Quality
Make sure to pick a PCM that’s made of durable and made of high-quality materials. Otherwise, you might find yourself in inconvenient or dangerous situations, like your car suddenly shutting down in the middle of driving.
The best way to ensure the quality of your new PCM is to order it from a trusted brand.
How Much Does a PCM Repair Cost?
If your PCM only needs to be reprogrammed for it to work properly again, you can expect to spend anywhere between $80 and $150 to repair it.
The PCM reprogramming might remove errors or bugs in the software and restore the computer’s great performance. However, if the PCM itself is damaged, you’ll need to replace it entirely.
What are the Maintenance Tips for PCM?
While PCM is designed to be durable, proper care and maintenance will keep it functional for a longer period and avoid expensive breakdowns. Consider the following tips to keep your PCM well-maintained:
- Professional Installation: Keep PCM repair or replacement to trained professional technicians to prevent improper handling and programming.
- Regular Diagnostics: Perform regular OBD-II scans to catch problems early, before they become major issues.
- Protect Against Moisture: Seal the PCM and store the PCM dry, particularly in monsoon or wet climates.
- Maintain a Healthy Battery: Voltage spikes from a weak or dying battery can ruin sensitive PCM circuits. Regularly monitor your battery and alternator.
- Prevent Bad Jump-Starting: Poor jump-starting can lead to electrical surges. Use proper techniques to prevent PCM damage.
- Repair Faulty Wiring Immediately: Faulty or corroded wiring will send faulty signals or overload the PCM. Repair any obvious wiring faults immediately.
- Use Recommended Fuel and Fluids: Low-grade fuel will cause the sensors to fail and stress the PCM. Use recommended fuel grades, oil, and transmission fluid grades.
FAQs.
Q: Can You Fix A PCM?
You can fix a PCM. But in this case, it could mean replacement. This is because most remanufacturers will likely not repair a faulty PCM. Replacement could be in two forms. It’s either you’re buying a new one or you’re rebuilding.
Rebuilding occurs if the compatible PCM isn’t available or you want to replace it with an old PCM. In this case, you will send your old PCM to a remanufacturer so that they can build the exact one.
Q: Can You Put A Used PCM In Your Car?
Yes, you can put a used PCM in your car. But ensure you take the old PCM you have to your dealer. This ensures that there is a match between your barcodes and the used PCM you want to use.
Also, note that you will have to flash the PCM if you’re using one from a car with factory security. If your car comes with a factory setting, you will need a PCM from a car without it. Then program the pin into it for it to work well.
If the car has no factory setting, swap the PCM, and you’re good to go. Not to worry, your car will work well.
Q: How Do You Reset The PCM?
After a problem is detected and fixed, the PCM will be left with some error codes. Resetting the PCM will help erase all these error codes. To learn how to reset the engine control module or PCM, follow the steps below.
- Open the hood of your car
- Disconnect the negative battery wires to cut the power off the PCM. You will need a wrench to unlock the locknuts. After which, you pull out the cables.
- After five minutes, reconnect the negative cord to the battery.
- Shut the hood of your car. Your PCM is now reset.
Q: Does The PCM Control The Transmission?
The PCM controls the two main car components, the engine and transmission. So yes, it controls the transmission, but this is true only for cars with automatic transmissions.
So if your car works on a manual transmission, the PCM has no business with it. So you can ask, can a bad PCM cause transmission problems? The answer is yes because it’s the PCM that controls it.
Q: Are PCM And ECM The same thing?
I would have probably given a yes or a no answer, but that wouldn’t answer the question. So PCM vs. ECM, this is what you need to know.
The power control module controls both the engine and transmission for cars with automatic transmissions. This is true, especially for recent models.
In addition, old cars with transmissions use the ECM and the transmission control unit(TCU).
So while the ECM controls the engine, the TCU controls the transmission. For cars with PCM, know that the ECM and TCU are incorporated into one onboard computer called the PCM.
So, whether the PCM and the ECM are the same depends on the context of usage. If a car uses only the ECM, it will serve the purpose of a PCM. But if a car uses both of them, ECM and TCU, then the ECM is not the same as the PCM.
Final Words
Having walked you through the PCM and its function in your car, you can see how powerful it is and that your car needs it. But wrap it up, what is a PCM in your car?
The PCM is the brain of your vehicle. It manages both the engine and transmission together with many other car components.
The only reason it works so well is that many car sensors are connected to it. And whatever work it does is based on the information it receives from the sensors.
If any sensor or the PCM fails, your car will malfunction or even damage other car parts. So ensure you replace bad PCM if you notice it.