Open Loop Fuelling

Open loop fuelling does not rely on information from the HO2S, but the air/fuel ratio is set directly by the ECM, which uses information gained from the ECT, MAF/IAT, the TP sensors and also the vehicle speed sensor (VSS). The ECM uses open loop fuelling under the following conditions:
^ Cold start.
^ Hot start.
^ Wide open throttle.
^ Acceleration.

The ECM uses open loop fuelling to control fuel quantity in all non adaptive strategy conditions. The ECM implements fuelling information carried in the form of specific mapped data contained within its memory.

Because there is no sensor information (e.g. HO2S), provided back to the ECM, the process is called an 'open loop'.

The ECM will also go into open loop fuelling if a HO2S fails.