Circuit Description

WARNING: This page is about a different car, the 2002 Isuzu Trooper. However, it is still accessible from the selected car via links, so may be relevant.

PCM supplies a bias voltage of about 450 millivolts between HO2S high and low circuits. When measured with a 10 megohm DVOM, display may be as low as 320 millivolts. HO2S varies voltage within about 1000 millivolts when exhaust is to rich, down to about 10 millivolts when exhaust is lean. PCM constantly monitors HO2S signal during closed loop operation and compensates for a rich or lean condition by decreasing or increasing injector pulse width as necessary. If Bank 1 HO2S voltage remains at or near 450 millivolts bias for an extended period of time, DTC P0134 will set, indicating an open HO2S signal or HO2S low circuit. HO2S heaters are used to minimize amount of time needed for closed loop fuel control operation and to allow accurate catalyst monitoring. HO2S heaters greatly decrease time required for Bank 1 HO2S No. 1 and Bank 2 HO2S 1 to become active. HO2Ss are required by post-catalyst monitor sensors to maintain sufficiently high temperature for accurate exhaust/oxygen content readings further from engine.

When DTC sets, PCM illuminates MIL on second trip after fault was detected. PCM will store conditions present when DTC was set as freeze frame data in the FAILURE RECORDS data. Vehicle with operate in Open Loop mode only.

PCM will turn MIL off on third consecutive trip cycle during which diagnostic runs and fault is no longer recognized. A history DTC P0134 will clear after 40 consecutive trip cycles during which diagnostic runs and fault is no longer recognized. DTC can be cleared with scan tool, or by disconnecting battery voltage feed to PCM.