On-Off Ratio Test Description

The on-off ratio tests the operation of the O2S (Lambda) control system and additionally, recognizes certain malfunctions present during the test. Malfunctions are distinguished between those that occur with the ignition ON and those that occur with the ignition at CTP (idle).

The on-off ratio can be checked with the on-off ratio tester or with the analyzer. For this purpose, the purge lines to the engine must be disconnected at both purge control valves and closed with plugs. See Figure and Figure . Check on-off ratio at closed throttle speed and at 2500 RPM. A readout of 50% or an oscillating needle indicates that all input signals and the O2S control system are okay. Readouts of 10% to 90% or 95% refer to a particular malfunction source. See COMPLAINT RELATED DIAGNOSTIC CHART (SECTION 12)  under TROUBLE SHOOTING. In addition, after testing the on-off ratio, an impulse readout must be performed using the impulse counter scan tool.