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The ABCs (and BAROs) Of Engine Management Systems


10/16/2013
By Larry Carley

Engine management systems are programmed for specific vehicle applications, and sometimes even the sensors for the same year/make/model may vary depending on the engine or transmission used, the state where the vehicle is registered or the emission standards to which the vehicle is certified.
 
The Engine Management System includes the Powertrain Control Module (PCM) and all of the engine’s various sensors. Looking up engine management replacement parts for a customer’s vehicle usually requires the year, make and model of the vehicle, the engine size (or engine VIN code), the transmission type (manual or automatic), and in some cases the OEM part number or vehicle VIN number to correctly identify the part.

Engine management systems are programmed for specific vehicle applications, and sometimes even the sensors for the same year/make/model may vary depending on the engine or transmission used, the state where the vehicle is registered or the emission standards to which the vehicle is certified. California vehicles (and Northeast states that follow California emission standards) often have different engine management components than federally certified vehicles.

Understanding Engine Management Systems also means having a working knowledge of the alphabet soup of acronyms that are used to identify many of the common sensors. Here are a few you should know:
BARO — barometric pressure sensor
CKP — crankshaft position sensor
CMP — camshaft position sensor
ECM — engine control module (same as PCM or ECU)
ECT — engine coolant temperature sensor
ECU — electronic control unit (same as PCM or ECM)
HO2S — heated oxygen sensor
IAC — idle air control
IAT — intake air temperature sensor
ISC — idle speed control
KS — knock sensor
MAF — mass airflow sensor
MAP — manifold absolute pressure sensor
O2S — oxygen sensor
PCM — powertrain control module (same as ECM or ECU)
TPS — throttle position sensor
VAF — vane airflow sensor
VSS — vehicle speed sensor

Most replacement sensors are basically plug and play. The old sensor is replaced with the new one, and the vehicle is ready to roll. However, any fault codes that were stored in the engine computer should be cleared with a scan tool following the installation of the new sensor. Some types of fault codes can may prevent the engine computer from using certain data or inhibit certain control functions. Consequently, if the codes are not cleared, the engine management system may not function normally.

If a PCM is being replaced, the PCM must be programmed for the specific vehicle it will be installed in. Some suppliers of reman PCMs will do this when the PCM is sold, but you have to provide them with the application information so they can load the correct software into the computer. In other instances, the computer comes without any calibration and the technician has to do the programming using a J2534 pass-thru tool or scan tool.

On older GM and Ford computers (1995 and pre-OBD II), the programming is on a calibration PROM (Program Read Only Memory) chip, which can be swapped from the old PCM or replaced with a new one. On most 1996 and newer vehicles with OBD II, the PCM is flash programmable so no chip swapping is required.














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