Powertrain control module: Difference between revisions

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{{Short description|Automotive component used on motor vehicles}}

{{howto|date=May 2012}}

[[File:An ECM from a 1996 Chevrolet Beretta- 2013-10-24 23-13.jpg|thumbnail|A PCM from a 1996 [[Chevrolet Beretta]].]]

A '''powertrainpower-train control module''', abbreviated '''PCM''', is an [[automotive industry|automotive]] component, an [[electronica control unit]] (ECU), used on [[motor vehicle]]s. It is generally a combined control unit,controller consisting of the [[engine control unit]] (ECU) and the [[transmission control unit]] (TCU). On some cars, such as many Chryslers, there are multplemultiple computers: the PCM, the Transmission Control UnitTCU, and the Body Control Module (BCM), for a total of three separate computers as an example. These automotive computer'scomputers are generally very reliable. The PCM commonly controls more than 100 factors in a car or truck. There are many hundreds of error codes that can occur, which indicates that some subsection of the car is experiencing a problem. When one of these errors occurs, usually it will turn on the "check engine" light on the dashboard. The PCM is one of potentially several onboardon-board computers, or essentially the "brain" of the engine control system.<ref>{{cite Whenweb the|url=http://www.aa1car.com/library/pcm.htm "brain"|title=Powertrain doesControl not function correctly, neither will the engine or anything else that the microprocessor controls, which may include the charging system, transmission, various emission controls and communications with other onboard control modules. TheModule (PCM) should|publisher=AA1Car be replaced only when it is diagnosed to be defective.|access-date=2014-12-20}}</ref>

On board Diagnostic (OBD II) diagnostic trouble codes that typically indicate a fault with the powertrain control module include:

*P0600....Serial Communication Link

*P0601....Internal Control Module Memory Check Sum Error

*P0602....Control Module Programming Error

*P0603....Internal Control Module Keep Alive Memory (KAM) Error

*P0604....Internal Control Module Random Access Memory (RAM) Error

*P0605....Internal Control Module Read Only Memory (ROM) Error

*P0606....ECM/PCM Processor

*P0607....Control Module Performance

*P0608....Control Module VSS Output

If you see any of these codes when diagnosing the vehicle with a code reader or scan tool, it may mean the PCM has failed and must be replaced. There can be other reasons for these codes as well, so the presence of any of these codes does not definitively mean the PCM needs to be replaced. Additional diagnostic tests will usually be necessary to confirm the problem is really the powertrain control module and NOT something else. Refer to the OEM diagnostic charts for what these tests are. Usually it involves checking certain inputs to the PCM to see if it outputs the correct response. No response or an incorrect response usually means the PCM is defective and needs to be replaced. Professional Automotive Technicians use extremely expensive equipment ($4,000 to $8,000) to do the extensive and complicated diagnostics that required before eliminating all other possibilities, to be able to arrive at a firm conclusion that the PCM has failed.

The primary inputs to the PCM come from many sensors, of different types, that are spread around the car. Most of them are oriented toward engine management and performance. These sensors fail at a much higher rate than any of the computers do.

Early use of the powertrain control module dates back to the late 1970s{{fact|date=February 2017}} - official phasing in{{clarify|date=February 2017}} of the PCM occurred during the early 1980s when used in conjunction with electronic controlled [[carburetor]]s and [[lockup torque converter]]s (at the time conventional 3-speed automatics received lockup converters at the same time overdrives were introduced{{fact|date=February 2017}}).

==Accurate PCM Identification==

Because there are so many different PCMs, accurate identification of the PCM and its correct replacement is absolutely essential to prevent unnecessary returns. Accurately identifying the PCM requires not only the vehicle year, make, model and engine size, but also the OEM part number on the PCM itself. Most supplier catalogs list replacement PCMs both ways. Many PCMs appear to be exactly the same on the outside (same sized box and connectors) but may be wired or calibrated differently inside.

If the wrong PCM is installed in a vehicle, it may run but probably will not run well. Close enough is not good enough when it comes to replacing PCMs. It must be the correct replacement to work right. Always refer to the OEM number on the PCM and look it up in the suppliers cross reference index to find the right part. On some occasions, after the new PCM is installed, it requires a "flash" operation, to "adapt it" specifically to the vehicle it is installed in. This flash can also set the computer into a more advanced condition that takes advantage of knowing the history of the vehicle, such as how many miles are on the car, how efficiently the fuel injection to the engine has been working, and other factors. This flash is usually performed at a dealer.

==Reasons for PCM Failure==

One way to reduce the risk of PCM warranty problems is to find out why the old PCM died. Determining the cause of death may not always be possible, but it may be essential to prevent the same thing from damaging the replacement PCM in some cases.

PCMs typically fail for one of two reasons: voltage overloads (often due to a short in a solenoid or actuator circuit) or environmental factors (corrosion, thermal stress or vibration). If the shorted solenoid or actuator is not found and repaired, the voltage overload it creates may damage the replacement PCM, too.

As for environmental factors, water is the main thing to avoid. If water gets inside a PCM, it can short circuits and set up irreversible corrosion that ruins electronic connections. Most re-manufacturers will not even attempt to repair a PCM if the vehicle it came out of was submerged in a flood. Replacement is the only option. Thermal stress and vibration can form micro cracks in circuit boards (which are repairable). This often has more to due with the ruggedness of the circuit design than operation factors in the vehicle itself.

==Unnecessary PCM Returns==

All too often, technicians tend to blame that which they understand least. If an engine is not running right and the cause is not obvious, they may blame the computer. Throwing parts at a problem in an attempt to solve it may be good for the parts business, but when a customer brings a PCM back because it failed to fix their problem, nobody wins. Warranty returns on complicated and expensive components like powertrain control modules are an ongoing problem that costs everyone money.

Over 50 percent of PCMs that are returned under warranty (either because the PCM failed to fix a performance problem or because the engine did not run properly after it was installed) have nothing wrong with them. It appears evident people just swap computers to see if a different PCM will fix their problem.

==Other names==

Returning a PCM can be troublesome because there is no way of knowing if it is still "good" or not, once it has been installed on the car. Someone may have crossed some wires, zapped the PCM with too much voltage, or otherwise adversely affected it. The PCM should be tested and verified before it can go back on the shelf and be sold to somebody else. Unfortunately, there is no easy way of testing the part at the retailer. The PCM has to be hooked up to a sophisticated simulator that exercises all of the computer's input and output circuits to make sure it works correctly, so it has to go back to the supplier to be retested. If no fault is found, it can be repackaged and put back into stock. Because of the difficulty in verifying the part is in good condition, many stores have a policy of no returns or refunds on electronic components.

'''Engine control unit''' is also called:

* PCM: Power-train control module (Ford, [[GM Family II engine|GM]], JLR)

* ECM: Engine control module

* Injection control unit ([[Peugeot]],<ref>{{cite web |url=http://www.obdtester.com/psacom-eculist/peugeot/607_1999_2004_van |title = PSA-COM - supported Peugeot 607 1999-2004 VAN control units}}</ref> [[Citroën]], [[Fiat]], Alfa, [[Lancia]])

* DME/DDE: Digital Motor Electronics / Digital Diesel Electronics ([[BMW]],<ref>{{cite web |url=http://obdtester.com/bimcom-eculist/bmw/5/2008_e60_e61 |title = BimCOM - supported BMW 5 control units}}</ref> [[Mini (marque)|Mini]])

* ECU: Electronic control unit / Engine control unit

==Bibliography==

*{{cite book |first=James E. |last=Duffy |authorlink=James E. Duffy |year=2003 |title=Modern Automotive Technology |publisher=Goodheart-Willcox Company |edition=6th |isbn=1-59070-186-0}}

*{{cite book |first=William B. |last=Ribbens |authorlinkauthor-link=William B. Ribbens |edition=6th |year=2002 |title=Understanding Automotive Electronics |publisher=Elsevier |isbn=0-08-048149-3}}

==References==

{{cite book |first=William B. |last=Ribbens |authorlink=William B. Ribbens |year=2002 |title=Understanding Automotive Electronics}}

{{Reflist}}

[[Category:Embedded systems]]

[[Category:Power control]]

[[Category:Engine technology]]