Powertrain Control Module (PCM), It’s Purpose and Location

The Powertrain Control Module (PCM), is the on-board computer that can be found in most cars and trucks. Most vehicle manufacturers began including PCMs during the 1980s, and the computer system has become standardized over the years. The PCM is the main computer in a vehicle and is the main brain behind the engine control system. Unfortunately, when the PCM is not functioning correctly, the engine and many other functions that are controlled by the PCM will not function correctly either. This would include parts of the electrical system such as the charging process, communications with other on-board control modules, emission controls, and the transmission. If the Powertrain Control Module fails, the On-board Diagnostic system (OBD II) will give some trouble codes that help to determine the problem. In most cases, some form of auto repair will be necessary to fix the problem.

Where is the PCM Located?

The Powertrain Control Module (PCM) is located in different places depending on the vehicle. On some vehicles, it is located in the engine bay close to the firewall. In others, It can be buried behind or underneath other components in the instrument panel of the vehicle. it can also be hidden behind the console, or the climate control system. In a few vehicles, it can be found underneath a seat. In many cases, the seat has to be removed in order to access the PCM.

How Can You Tell if a PCM is Bad?

If the PCM is bad, or going bad, the vehicle will begin to display some problems. These problems could include the vehicle not starting, or the vehicle not holding a charge. The check engine light on the vehicle will also be constantly on to indicate that there is a problem with the vehicle. If the check engine light is on, an On-board Diagnostic (OBD II) scan tool or code reader can be hooked to the vehicle’s computer port to find out exactly what the problem is. There are many OBD II trouble codes that indicate a problem with the PCM, this includes codes P0600 through P0610. If the scan tool or code reader shows any of these codes, it probably means that the PCM has failed and needs to be replaced.

Can a Faulty PCM be Misdiagnosed?

In many cases, when an engine is running poorly and the cause is not easily found, technicians blame the vehicle’s computer. Nevertheless, replacing parts in an attempt to solve a problem is not good for either the vehicle or the auto repair business as it often means customers bring parts back. More than half of all the PCMs that are returned are a result of not fixing the problem. However, once a PCM is installed on a vehicle, there is no real way to know if it is still working. It is possible that the person installing it crossed some wires, or spiked the PCM with too much power. Therefore, before the PCM can be returned to the shelves and re-sold, it has to be tested. Unfortunately, most auto repair stores do not have the equipment necessary to do this. To test a PCM, it has to be connected to a simulator that works all the input and output circuits to ensure that everything still works correctly. Typically, this means that the PCM has to be returned to the supplier to be tested, and then repackaged and returned to stock if it is found to be good. Because of this, the price of PCM units and other electronic components are quite high, and many auto parts stores have a no refund or return policy on anything electrical.

What Causes the Powertrain Control Module to Die?

There are two main reasons why a Powertrain Control module goes bad, and knowing what has caused the problem may help to reduce the risk of the same problem from happening again. Environmental issues such as thermal stress, corrosion, or vibration can cause a PCM to die. The other main reason is usually a voltage overload. This can be caused by a short in an actuator circuit or solenoid. If the PCM has gone bad due to a voltage issue, if the shorted actuator or solenoid is not repaired, the overload is likely to happen again and damage the new PCM.
If a PCM dies due to water damage, it typically cannot be repaired and has to be replaced. However, vibrations and thermal stress can cause micro-cracks in the circuit boards. These can usually be repaired quite easily by a PCM re-manufacturer.

When replacing the PCM, it is important that it is replaced with one that is compatible with the vehicle. A lot of PCMs look identical, but can be calibrated or wired differently. If the wrong type of PCM is installed in a vehicle, it may not run, or it may run badly. In order to accurately identify the PCM, the auto parts store or mechanic will need to know the make, model, engine size, and year of the vehicle. They will also need to know the OEM part number located directly on the PCM itself.