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2007 Toyota Sienna P0138 O2 Sensor Issue: Light Comes On at Highway Speeds

Model: 2007 Toyota Sienna Fault Code: P0138 Posted: 2011-01-23 18:32

I own a 2007 Toyota Sienna Limited AWD and recently encountered a check engine light with code P0138 (High Voltage O2 Sensor Bank 1, Sensor 2). The issue first appeared a month ago when both the check engine and VSC lights activated. The dealership claimed replacing the oxygen sensor would resolve it, but instead of paying $300 for a dealer-installed part, I opted to install an aftermarket Bosch O2 sensor for $80. The result: the warning light stays off in city driving but reactivates when I accelerate onto highways. According to my Haynes manual, here are the key diagnostic steps for a faulty O2 sensor: - Voltage test: The sensor reads between 0.2 and 0.9 volts using both a voltmeter and an OBD-II scanner (OBDwiz), staying within the expected range of 0.1–0.9 volts. - Heater resistance test: The heater shows 15.6 ohms, which falls within the normal range of 12–16 ohms. Battery voltage is also confirmed to be reaching the sensor. Both sensors passed these tests, leading me to suspect that the O2 sensor was not the root cause. To confirm this, I unplugged the B1S2 sensor and shortly after, code P0137 (Low Voltage O2 Bank 1 Sensor 2) appeared — a pattern observed in some Toyota Avalon owners linked to catalytic converter failure. Has anyone on a 2007 Sienna experienced this issue? Are there known wiring or harness problems with the bank 1 system, especially related to sensor circuits? Any additional troubleshooting steps for diagnosing electrical faults in O2 sensors? Steve

Related fault codes
P0138
Comments (5)
Anonymous 2011-01-24 05:56

You could perform all those tests, but it's safer and more reliable to install the correct OEM Toyota oxygen sensor from a dealership. I've found that aftermarket parts like Bosch don't always match factory specifications — they may not provide consistent voltage or heater performance in older models like the 2007 Sienna.

Anonymous 2011-04-02 15:18

I replaced the original B1S2 O2 sensor with a genuine Toyota part, and immediately P0138 disappeared. However, a new code appeared: P0031 (Low Voltage O2 Bank 1 Sensor 1). I'm hesitant to replace that one because it might indicate a manifold or wiring issue instead. Does anyone have insight into diagnosing bank 1 problems?

Anonymous 2011-04-02 19:29

That's a different diagnostic trouble code (DTC)! P0031 typically points to an electrical circuit fault — not a sensor failure. While P0138 is generally caused by a heater element issue in the O2 sensor, it can still produce normal voltage variations. In my experience, two-digit DTCs like this usually indicate an open or shorted wiring path rather than a failing sensor.

Anonymous 2011-04-03 13:04

I'm now seeing multiple issues on Bank 1 — P0138 and P0037 (Low Heater Voltage for B1S2). After re-installing the original B1S2 O2 sensor I suspected was faulty, the P0138 did not return during a long test drive. However, new codes appeared: P0037 and P0031. This strongly suggests an electrical problem in the wiring harness. How can I properly test for open circuits? Should I check voltage at the ECU, at the sensor end, and then progressively test between intermediate points?

Anonymous 2012-06-29 03:34

The O2 sensor you installed was likely not compatible with your 2007 Toyota Sienna. Some users have reported that incorrect sensors or reverse installation can cause false readings. I recommend having a certified mechanic install the correct OEM part. That said, manifold issues are unlikely here — P0138 typically reflects an electrical problem rather than a catalytic converter failure.