|LANCE’S CORNER – AUTO REPAIR HELP|
ONBOARD AUTOMOTIVE COMPUTER – EEC
The control module is calibrated to tailor system operation to a specific vehicle powertrain and emission configuration. Calibration of the control module is achieved either using ROM (read only memory) or a replaceable PROM (programmed read only memory) chip. Some control modules use an erasable PROM that can be recalibrated by downloading a calibration file from a computer. Some control modules use an adaptive learning strategy to tailor engine control to vehicle operating conditions. Idle speed, fuel delivery and is some cases, transmission shift points, can be modified to adapt to wear, malfunction or driving habits. Most adaptive learning strategy is contained in volatile memory circuits and is erased when battery power is removed from the vehicle such as during an auto repair project. This may affect vehicle operation until the strategy is relearned.
Most control modules operate system components by providing a ground path for the controlled component electrical circuit. The ground circuit is usually provided by transistors or internal driver modules contained inside the control module. Current handling capabilities of the transistors or driver modules is of moderate capacity, so system components are designed with a high enough resistance to limit amperage flow. Control module damage can result from high current flow from a shorted components. Prior to replacing a faulty control module, the circuit resistance of controlled components should be checked.
(Lance owned his own auto repair shop for 30 years before retiring in 2006.)