DTC P0156, P1157 Or P1158: Ho2S Circuit Malfunction: Condition

WARNING: This page is about a different car, the 2002 Mazda 626. However, it is still accessible from the selected car via links, so may be relevant.

DTC is set when Powertrain Control Module (PCM) detects input voltage from left rear heated oxygen sensor (HO2S) heater is less than .14 amp or more than 3 amps after front HO2S heater has been on for 60 seconds. This is an intermittent monitor. MIL is illuminated when PCM detects malfunction during 2 consecutive drive cycles. Possible causes are:

Left rear HO2S malfunction.
Open in circuit between main relay and left rear HO2S.
Short or open in circuit between PCM and left rear HO2S.
PCM malfunction.