Oxygen sensor heater circuit malfunction

P0135 - upstream of catalyst (front) / rear (RH) bank

P0141

• 4-sensor: downstream of catalyst (rear) / rear (RH) bank
• 3-sensor: upstream of catalyst (middle) / rear (RH) bank

P0147 - downstream of catalyst (rear)

P0155 - upstream of catalyst (front) / front (LH) bank

P0161 - downstream of catalyst (rear) / front (LH) bank

Emissions Equipment Information

Three o² sensor system (KL engine with one catalytic converter) - A front sensor is positioned on the LH bank and a middle sensor is positioned on the RH bank upstream of the catalyst for closed loop fuel control.  A rear sensor is mounted downstream of the catalyst to monitor its efficiency.

Four o² sensor system (KJ / KL engine with three catalytic converters) - Front sensors are mounted upstream of the RH and LH warm-up three-way catalyst (WU-TWC) for closed loop fuel control.  Rear sensors are mounted downstream of the WU-TWCs to monitor their efficiency.

Detection Conditions

• If the oxygen sensor heater circuit voltage remains too high while the circuit is off or the voltage remains too low while the circuit is on, the ECU determines that the oxygen sensor heater circuit is faulty.

Diagnostic Support Notes

• This is an intermittent monitor (OXYGEN SENSOR HEAT)
• Check engine illuminates if the ECU detects the above malfunction condition in two consecutive drive cycles
• PENDING CODE is available
• FREEZE FRAME DATA is available
• DTC is stored in ECU memory

Possible Causes

• Oxygen sensor malfunction
• Open circuit between the main relay terminal D and oxygen sensor terminal C
• Open circuit between oxygen sensor terminal D and ECU
• Short to ground circuit between oxygen sensor terminal D and ECU
• Poor connection at oxygen sensor or at ECU connector
• Short to power circuit between oxygen sensor terminal D and ECU
• Shorted oxygen sensor terminal or ECU terminal
• ECU malfunction

[P0135 / P0141 / P0147 / P0155 / P0161 - From 1998 and 2002 Mazda Millenia factory service manuals]