Oxygen Sensor Heater, P0032 | Toyota 4Runner 

🚗 2004 Toyota 4Runner 4.7L

• P0032 Bank 1 Sensor 1 Heater Control Circuit High
• Customer has previously changed the Oxygen Sensor B1S1 with an aftermarket Denso part, which didn’t fix the problem. Same code came back within a few seconds after starting the engine.

🩺 Diagnosis

Where is a Bank 1?

• Bank 1 on 4.7L Toyota is on the driver side (left)
• Bank 1 on 4.0L Toyota is on the passenger side (right)

Using an ohmmeter, I’ve tested a heater element resistance (two wires same color on the oxygen sensor):

• In this case, the aftermarket Denso heater resistance measured 3Ω drawing 3A of current.
• The good OEM Denso heater measured 13Ω drawing only 0.8A.
• According to my research, aftermarket Denso O2 sensors don’t work well on Toyotas, but this replacement appears to have a shorted heater element.

RED = O2 Heater Control B2S1 (OEM)
Blue = O2 Heater Control B1S1 (aftermarket)
Green = O2 Heater current B1S1 (aftermarket)

Here is a closer snapshot on what happened, when ECM tried to energize the aftermarket O2 sensor.

Blue = O2 Heater Control B1S1 (aftermarket)
Green = O2 Heater current B1S1 (aftermarket)

Note that as the ECM pulls the heater wire (ground side) to a good ground (0V), it meets a lot of demand (lots of current being drawn by a heater, 2.8A), and before long ECM cuts its ground control to preserve its transistors from burning.

If the blue trace looked the same (didn’t reach good ground) and the current didn’t pass 1A (didn’t demand much), I would suspect a bad ground to the ECM or the ECM itself as the culprit. But since the current dipped that low, then there is definitely something wrong with the wiring to the O2 sensor or the O2 sensor itself.

RED = O2 Heater Control B2S1
Blue = O2 Heater Control B1S1
Green = O2 Heater current B2S1 (OEM part)