How To Detect Powertrain Control Module Problems

A powertrain control module combines the functions of engine and transmission control modules. Most late model vehicles feature a PCM with integrated ECM and TCM systems. A powertrain module may appear to be a single unit on the outside, but this component usually consists of engine and transmission modules that have separate processors. PCMs began being used in vehicles around 1996, though the terms manufacturers use to refer to this part vary.  Check the vehicle manual for a particular make and model to determine the original equipment manufacturer terminology for this on-board computer.

How Do Powertrain Control Modules Function?

PCMs perform all of the functions formerly assigned to engine control modules and transmission control modules. These systems are designed to support the engine and the transmission in vehicles that have automatic transmissions. The integrated design works to increase fuel economy and reduce emissions. Vehicles that have manual transmissions primarily rely on these modules to regulate the engine.

A working powertrain control module is essential for a vehicle to run properly, as this system regulates over 100 factors. The powertrain module plays an essential role in monitoring performance, adjusting the ratio of air to fuel in engine cylinders and regulating engine revolutions per minute for timing ignition and setting idle speed. Vehicle owners who are experiencing issues with any of these systems or settings should rule out mechanical problems prior to performing diagnostic testing on the powertrain module.

What Are the Signs of a Faulty Powertrain Control Module?

Most of the problems that occur with the engine or transmission on a vehicle are mechanical. In a smaller number of instances, a faulty powertrain module is to blame. The clearest indication of computer failure are a variety of malfunction indicator lights that turn on and off randomly. A check engine light or any other light on the dashboard may illuminate and turn off due to a powertrain module not being able to compute sensor data and adjust the function of critical engine or transmission components.

If the illumination of indicators does not correspond to the actual conditions of various vehicle systems, a malfunctioning powertrain module is the most likely cause. Even a number of problems that seem mechanical in nature can be caused by a faulty powertrain module that is not relying on accurate sensor readings to control engine and transmission functions. This can cause misfiring, stalling or heightened emissions and could lead to serious mechanical issues down the road.

A failed powertrain module may prevent the engine in a vehicle from starting. This system positions the crankshaft and times ignition sequences. Depending on whether the system is capable of functioning at all, a vehicle may enter limp mode. This safety setting makes it possible to maneuver a vehicle out of traffic or to a service location, but may limit acceleration or top speed. Because PCMs regulate engine and transmission functions, a vehicle in limp mode may make hard shifts due to a protective increase of fluid pressure on the clutch packs or other components.

Can Powertrain Control Modules Be Fixed?

If a powertrain control module is malfunctioning, reflashing may be effective. This process involves updating the manufacturer’s software for powertrain module function. The latest update may help to resolve problems such as incorrect diagnostic codes, poor fuel economy, excessive emissions or persistent issues such as rough idle, hard starts or hesitation when shifting gears.

It will be necessary to replace a failed powertrain module with another on-board computer that is designed and programmed for use in a particular vehicle make and model. PCMs built to original equipment manufacturer specifications can be very costly parts. If possible, purchasing a pre-programmed powertrain control module ready for installation may reduce labor costs.

How Much Do Replacement PCMs Cost?

PCMs are typically more expensive than separate engine control modules or transmission control modules. These integrated systems are essential for both vehicle systems to function in accordance with manufacturer and part specifications. OEM parts can cost up to $1,000 or even more depending on the vehicle make and model. Replacing this part can cost even more when done through a dealership with a powertrain control module that requires reprogramming. The most affordable replacement PCMs come pre-flashed with the latest version of vehicle software.

Do PCMs Require Reprogramming?

A faulty powertrain control module may need to be reflashed or reprogrammed. The software in this system is particular to a vehicle make and model and may be updated by the manufacturer to solve common problems. If many vehicle owners report problems due the system’s inability to accurately detect sensor readings and regulate engine or transmission functions accordingly, a manufacturer may be able to fix these problems on the software level.

PCMs rely on read-only memory or ROM to store vehicle settings. Whenever the system is reflashed or the battery has been disconnected, a powertrain module may have to relearn fuel mixture, idle speed or shifting settings. Relearning differs from reprogramming in that a functional module will be able to automatically adjust these settings. It may be possible to reset the idle speed by lightly depressing the gas pedal or taking a short drive. Depending on the issue, it may be necessary to reset a module with a scan tool. If the powertrain module in a vehicle has failed, it will be necessary to either have a new module reprogrammed by a dealer or purchase a pre-programmed module that has been flashed with the most recent software.

Powertrain control modules combine the functions of an engine control module and transmission control module. For this reason, a vehicle with a faulty PCM may not operate at all. The engine may crank, but safety features prevent major parts from sustaining damage in the event of failure. Depending on the condition of the powertrain module, it may be possible to reflash and update the system. If this critical system does not function reliably, it should be replaced with a vehicle-specific component from Importapart. A new powertrain control module that meets manufacturer’s specifications will be shipped within one business day of ordering.