Powertrain Control Module (Pcm): Notes

The Powertrain Control Module (PCM) is located under instrument panel on passenger side. See Fig 1 . PCM controls fueling, idle speed, exhaust emissions, transaxle shifts, ignition timing, cooling fans and cruise control functions. The PCM can also recognize operational problems, alert driver through "SERVICE ENGINE SOON" MIL and store codes which identify problem areas for technician.

In order to perform all of these functions, PCM contains two processors, each with its own outputs, inputs, memory and program. Two processors function together by sharing input data, but they also function independently by controlling only certain outputs. The function of each processor can be loosely categorized as engine controls or transaxle controls. The only functions performed by both processors is diagnosis of serial data line, battery power circuits and PCM PROM. Because each processor diagnoses these on their own, each sets its own code in case of a failure. For example, each time battery is disconnected, two codes will set, P052 and P109.

The PCM is connected to engine wiring harness by three 32-pin connectors. Each connector is color coded - red, white or blue - and each row of pins in these three connectors has been given a unique alphabetical designation; A or B (red connector), C or D (white connector) or E or F (blue connector.

The PCM consists of two separately serviceable parts: PCM and PCM PROM. The PROM plugs into PCM and is located under PROM cover. See Fig 2 .