Rear heated oxygen sensor (HO2S), aging
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2006 Volvo S80, 2005 Volvo S80, 2004 Volvo S80, 2003 Volvo S80, and 2002 Volvo S80. However, it is still accessible from the selected car via links, so may be relevant.
The control module checks the rear heated oxygen sensor (HO2S) dynamics. The control module checks that the probe has registered both lean and rich fuel mixtures. If this is the case, a signal is transmitted so that the probe signal is changed. Diagnostic trouble code (DTC) ECM-2A1A / 2B1A is stored if the rear probe has still not registered lean or rich fuel mixture. The diagnostic trouble code (DTC) is also stored if the switch over time from lean to rich fuel mixture is too long.