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If you are a car owner or who drives a car around, a Powertrain Control Module (PCM) is a part of a vehicle you should already be familiar with. Especially when doing regular maintenance, your mechanic may have mentioned something about it.
So what is a PCM? This article will answer that question, show its location in your vehicle, what it does, and some of the common issues that plague this car part.
What is Powertrain Control Module?
The Powertrain Control Module (PCM) is an important car component that plays a significant role in your vehicle’s internal system. It receives data from various sensors that help optime performance and fuel economy. The PCM consists of two control modules; the Engine Control Module (ECM) and the Transmission Control Module (TCM).
Engine Control Module (ECM)
The ECM or Engine Control Unit ECU guarantees that your vehicle performs optimally. It monitors most of the sensors in the engine bay to manage the air-fuel mixture and regulate the pollution control systems in your car.
The ECM controls four major operating systems in your vehicle: the air-fuel ratio, idle speed, variable valve timing, and ignition timing. It uses sensors to adjust the oxygen-to-fuel ratio measured in your car's exhaust to identify an engine rich/lean reading in terms of air-fuel ratio.
Among these sensors are mass airflow, oxygen, and air-fuel. The ECM depends on sensors situated by the crankshaft and camshaft to track your vehicle's Revolutions Per Minute (RPM) and engine load by measuring the engine's speed of rotation.
Transmission Control Unit (TCU)
This one is responsible for managing your automatic or manual transmission. It works with the engine and transmission to keep your car moving. This calculates the ideal time and place to change gears to make your driving experience the best it can be.
It receives signals from the PCM about throttle position, engine RPMs, vehicle speed, and other operating conditions. It then commands the transmission to control shifting patterns and torque converter lockup.
What is the function of a PCM in a Car Engine?
The PCM is responsible for the air-to-fuel ratio, which is necessary to maintain engine efficiency and emissions levels. It controls ignition timing, fuel delivery, engine valve timing, emissions functions, turbo boost pressure in turbocharged engines, idle speed, throttle position, and cruise control.
The PCM controls the automated gearbox in vehicles without a separate TCM. It also connects with the Body Control Module, ABS/traction control/stability control module, electronic steering, different lighting modules, and other subsystems to communicate information, data, and interactive features.
Where is PCM Located in a Car?
Knowing the location of the PCM in any car is an essential piece of knowledge to help you in doing repairs when necessary. In newer vehicles, the PCM is usually located in a black box near the driver’s side of the engine compartment. It may be labeled “PCM” or “Powertrain Control Module.”
What are PCM Sensors?
Many sensors feed data to the PCM. Each of these sensors plays a vital role in how the engine runs. The PCM uses this data to decide how to control the engine. Some of these sensors include:
Mass Air Flow Sensor
The Mass Air Flow (MAF) sensor is a crucial component of your vehicle's electrical fuel injection system. It's positioned between the air filter and the engine's intake manifold. The mass air flow sensor monitors how much air enters the engine or how much airflow there is.
Throttle Position Sensor
The Throttle Position Sensor (TPS) is located on the throttle body. It monitors the position of the throttle valve and sends that information to the PCM.
Oxygen Sensors (O²S)
There are usually two oxygen sensors before and one after the catalytic converter. The oxygen sensor before the converter measures how much oxygen is in the exhaust gases. The oxygen sensor after the converter measures how much oxygen is left in the exhaust gases.
Coolant Temperature Sensor
The Coolant Temperature Sensor monitors your engine's coolant temperature. It sends this information to the PCM to control the engine cooling system.
Intake Air Temperature Sensor
The Intake Air Temperature Sensor monitors the engine's air temperature. It sends this information to the PCM to control the air/fuel mixture.
The Knock Sensor monitors the engine for knocking or pinging. It sends this information to the PCM to adjust the ignition timing to prevent knocking.
Importance of the PCM
In addition, to its ability to control the engine and transmission, the PCM is also responsible for various safety features on your vehicle. These can include:
- Seatbelt Pretensioners
- Airbag Control
- Anti-Lock Brakes (ABS)
- Electronic Stability Control
Each of these systems relies on inputs from various sensors located all over the car. The PCM controls how each system works based on data from these sensors. It is responsible for automatic headlights and rain-sensing wipers. It can monitor your driving habits and make suggestions to improve fuel economy.
Furthermore, it also has a significant role in remote vehicle immobilization that is known for providing remote keyless entry, anti-theft, and other such features. So how does the PCM works with remote vehicle immobilization?
For example, your car has a keyless entry feature. If your vehicle is parked within a specific range, you can unlock your car doors without physically inserting a key into the door lock. For this to work, the PCM needs to work correctly, and it needs to be receiving the correct signal from your fob.
Symptoms of a Faulty Powertrain Control Module
If you are a long-time driver, you may have experienced some drivability issues caused by a failing PCM. If you have noticed any of these issues with your vehicle, you might have a bad powertrain control module, and you need to inspect and replace it if necessary.
Engine Stalling or Misfiring
One of the most common noticeable symptoms of a bad or failing PCM is engine stalling. If there is an issue with the PCM not sending the correct signal to the fuel injectors, this can cause cylinders to misfire or not fire at all. This can lead to engine stalling while driving or even a no-start condition.
Hesitation or Lack of Power
Another common symptom of a bad PCM is hesitation or a lack of power when accelerating. This can be caused by incorrect fuel mapping and other issues with the engine.
Erratic Throttle Behavior
Erratic throttle behavior is another symptom that may indicate a problem with the PCM. This can include sudden surging or decelerating, even when no input is given to the throttle pedal. In some cases, this may be accompanied by strange noises from the engine compartment.
Check Engine Light is On
One of the most common symptoms of a problem with the PCM is the illuminated Check Engine Light. When the PCM monitors the engine's systems, it keeps track of all sensor readings. If any sensors provide readings out of the normal range, it will set a trouble code and turn on the Check Engine Light.
In some cases, there may also be accompanying codes stored in the PCM that can help to diagnose the issue.
Poor Fuel Economy
Another symptom related to a problem with the PCM is poor fuel economy. This can cause by several different factors, including spark timing issues, air/fuel mixture issues, or transmission problems.
Presence of Diagnostic Trouble Codes
When the PCM detects an issue, it will store error codes. These codes can be read with a scan tool and help diagnose the problem. Many error codes can be associated with problems with the PCM, so it's crucial to have the codes read and diagnosed by a professional.
In addition, diagnostic trouble codes may vary depending on which part of the PCM malfunctions. As mentioned earlier, PCM is integrated with the ECM and TCM, and each of these modules has its own set of trouble codes.
For example, the ECM may have codes for the oxygen sensors or air/fuel mixture issues, while the TCM may have codes for shifting gears. These are the sample codes for each module:
- P0171, P0172- OBD-II Trouble Codes for Lean Mixture
- P0300, P0301- OBD-II Trouble Codes for Multiple Cylinder Misfire
- P0404, P0405 - EGR System Failure codes
- U0100, U0102 - Lost Communication with ECM
- P0700, P0800 - Transmission Control System Malfunction codes
Troubleshooting the PCM
If you suspect that your PCM is not working correctly, the best way to test it is to take it to a professional mechanic or automotive specialist. However, if you are mechanically inclined, there are some things you can do to test it at home.
When you are driving, and you notice any of the symptoms listed above, you can do a few simple tests to try and determine if the PCM is at fault.
- Locate the PCM.
- Look specifically at the wiring harness. Check for damaged and replace it if necessary.
- Connect the scanner to the vehicle's OBD connector.
- Turn on the OBD scanner after plugging it in.
- The trouble code will give you an indication as to what might be wrong with your car's power.
- Turn on your ignition to start the engine.
- Press the scan button to begin scanning for codes on your scanning tool.
- Look up each code and temporarily skip the ones that do not apply.
- Determine whether you can handle the issue without a mechanic, as any mistakes may worsen the problem. However, some problems may only require restarting the PCM, which may be accomplished by safely disconnecting the vehicle's negative battery cable, waiting for the power to drain, and reconnecting.
How Much Does a PCM Cost?
The PCM is costly, so it should not be replaced unless there is good evidence that a problem is within the PCM itself and not something else. However, it may vary depending on your vehicle's make, model, and year.
The ideal cost would be around $600 to $1200, and the labor will cost another $120 to install and program the PCM. So, you can expect at least $800 for a PCM replacement.
Powertrain Control Module FAQs
1. What causes powertrain control module failure?
One of the most common reasons for a PCM failure is incorrect repairs. When an auto technician doesn't have the correct knowledge or experience to work on a particular system, they may end up causing more damage than good.
2. Do all cars have a PCM?
No, not all cars have a PCM. Older model cars may have an engine control unit (ECU) instead. The ECU is responsible for the same functions as the PCM, but it doesn't control the transmission.
3. How often should it be replaced or serviced?
There is no set schedule for replacing or servicing the PCM. However, it's good to have your vehicle's PCM checked periodically by a qualified technician.
4. Is the bad PCM affect the emission test?
If your PCM is not functioning properly, your car may fail its emissions test because it will emit too much smoke.
5. How can I prevent the PCM to damage?
The best way to prevent the PCM from being damaged is regularly servicing. Also, make sure to use the correct oil and filter for your vehicle.
The PCM is an integral part of your vehicle. It controls the engine and transmission and monitors the various sensors in your car. It also has a significant role in our safety and convenience, so make sure to have it serviced regularly to prevent damage.
We hope that this article has been helpful. If you have any questions, please feel free to contact us. Thank you for reading!