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]] (also known as an ECU) and the [[transmission control unit]] (TCU). ItOn some cars, such as many Chryslers, there are multiple computers: the PCM, the TCU, and the Body Control Module (BCM), for a total of three separate computers. These automotive computers 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 on-board computers, or essentially the "brain" of the engine control system.<ref>{{cite web |url=http://www.aa1car.com/library/pcm.htm |title=Powertrain Control Module (PCM) |publisher=AA1Car |access-date=2014-12-20}}</ref>

The onboard computer, or Powertrain Control Module (PCM),is the brains of the engine control system, so when the brain is not functioning correctly neither is 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. Once a diagnosis has been made (and we emphasize the word diagnosis), then and only then should the PCM be replaced.

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.

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

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}}).

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 'A'

P0609....Control Module VSS Output 'B'

P0610....Control Module Vehicle Options Error

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. 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.

==Other names==

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.

'''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==

UNNECESSARY POWERTRAIN CONTROL MODULE RETURNS. 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! So it is obvious a lot of people are swapping computers to see if a different PCM will fix their problem.

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

The trouble with returns is if the PCM has been on the car, you have no way of knowing if it is still "good" or not. Somebody may have crossed up some wires, zapped the PCM with too much voltage or who knows what? The computer needs to 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 doing that in a parts store. 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 - which means the PCM has to go back to the supplier, be retested, and if no fault is found, repackaged and put back into stock.

Be warned, though, that many parts stores have a policy of "no returns or refunds on electronic components."

WHY DID THE POWERTRAIN CONTROL MODULE DIE?

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 remanufacturers 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 microcracks 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.

ACCURATE POWERTRAIN CONTROL MODULE IDENTIFICATION

Because there are so many different PCMs, accurate identification of the PCM and its correct replacement is absolutely essential to prevent unnecessary returns. 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 for the application.

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. So if in doubt, always refer to the OEM number on the PCM and look it up in the suppliers cross reference index to find their

==References==

{{Reflist}}

{{Modern automotive technology james e.duffy}}

{{understanding automotive electronic.}}

{{auto-tech-stub}}

{{auto-part-stub}}

[[Category:Embedded systems]]

[[Category:Power control]]

[[Category:Engine technology]]