Low Voltage Correction - What do you mean by that? Is it me or you?...

 

THEORY OF OPERATION

Low-voltage or battery voltage correction mode (sub-mode) – is an ECM strategy or mode that is directed to increase fuel delivery in case of a low voltage condition. At lower operating voltages, the fuel pump’s rotational speed is much slower, with a corresponding drop in fuel pressure and volume as well. The injector reaction time also suffers with the lower voltage. To answer the lower voltage condition, the ECM increases injector pulse width, ignition coil dwell time and may also raise the idle speed (IAC counts) to compensate. The increase in these parameters corresponds to a stored correction factor stored in ROM memory (in a look-up table) and is used according to the severity of the voltage drop. The low voltage mode is activated as soon as the available voltage goes bellow a predetermined value (usually 12.6 volts) and can take place together with any of the other operating mode. Normally this mode is activated while cranking the engine, since the starter motor lowers the battery voltage while cranking. A possible problem relating to this mode is excessive resistance in the power feed circuit to the ECM, which would signal it to enter the battery correction mode and increase injector pulse. This condition would undoubtedly increase emissions and create an engine performance fault. If the technician suspects a low power feed voltage condition, proceed to check all fusible links, main ECM relays and connections that may cause high resistance in the circuit. On the other hand, a ground resistance problem may also be perceived by the ECM as a low voltage condition, since the ECM reference ground is probably higher than battery ground. The ground is as important as the power feed side in any automotive circuit.

 

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