2001 Toyota Sequoia Oxygen sensors

You have 2.

How many O2 sensors does a 4 cylinder have?
Two oxygen sensors Oxygen sensors are utilized by vehicles to help control emissions and make certain the exhaust system is running efficiently. In most newer vehicles equipped with 4 cylinder engines there are two oxygen sensors, one before the catalytic converter and one after.

How many o2 sensors does a 4 cylinder have? - WapCar

O2 sensor is mounted on exhaust system near engine before cat converter can't help with rest of question sorry

The Sequoia has two oxygen senros that are bolted into the exhaust pipes coming out of each manifold. They are located roughly under the front seats. There is a known problem with the Sequoiua's oxygensors not being properly bolted into the flange. The two nuts will cecome loose and fall off, and if you suddenly accelerate, the oxygen sensor pops out (of course it will be dangling). You have to put it back with new gasket and new nuts.

DTC P0125 OBD-II - Insufficient Coolant Temperature For Closed Loop Fuel Control
This means that the engine coolant temperature (ECT) sensor indicates that the engine has not reached the required temperature level to enter closed-loop operation within a specified amount of time after starting the engine. You will likely not notice any drivability problems.

A code P0125 may mean that one or more of the following has happened:
Insufficient warm up time
Low engine coolant level
Leaking or stuck open thermostat
Faulty coolant temperature sensor


DTC P0135 OBD-II - Oxygen O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 1)
This code refers to the front oxygen sensor on Bank 1. The heated circuit in the oxygen sensor decreases time needed to enter closed loop. As the O2 heater reaches operating temperature, the oxygen sensor responds by switching according to oxygen content of the exhaust surrounding it. The ECM tracks how long it takes for the oxygen sensor to begin switching. It the ECM determines (based on coolant temp) that too much time elapsed before the oxygen sensor began operating properly, it will set P0135. You will likely notice poor fuel economy the illumination of the MIL.

A code P0135 may mean that one or more of the following has happened:
O2 Heater element resistance is high
Internal short or open in the heater element
O2 heater circuit wiring high resistance
open or short to ground in the wiring harness


For additional details, feel free to contact us in the preivous code link.

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Toyota Sequoia has 4 oxygen sensors... two on each side. The ones in front of catalytic are position one, and, after are position 2.

Bank 2 is on passenger side, Bank 1 is on driver's side.

Hope this helps (remember to rate and comment this free answer).

P0037 - O2 Oxygen Sensor Circuit High Voltage (Bank1, Sensor2)

The Heated Oxygen Sensor (2) located rear of catalytic converter produces an output signal relative to oxygen storage capacity of catalytic converter. Ho2S 2 signal is less active than signal produced by front oxygen sensor. This code sets when HO2 Sensor voltage is greater than 999 mV for more than 2 minutes (time depends on model. Could be as high as 4 minutes)

Symptoms: There may be no noticeable symptoms except for MIL illumination. Possible high fuel pressure can over rich the system.

Causes: A code P0138 may mean that one or more of the following has happened:
* Faulty O2 sensor
* Short to battery voltage in O2 sensor signal circuit
* High fuel pressure (not as likely)


Here are some potential solutions:
* Replace O2 sensor
* Repair short to battery voltage in o2 sensor signal circuit

If you replaced the O2 sensor, then its possible that you have some electrical problem there; reset the codes first, and if this come on again, check in this link TSB P0037 electrical diagnostic procedure.

Keep us updated.

Trouble code P0031 means: Oxygen Sensor Heater Control Circuit Low - Bank 1 Sensor 1 .
Error code p0051:replace O2 sensor ($75-150 depending if OEM) before catalytic converter. need O2 socket ($10) to get at and tough to get to if vehicle isn't at least on a ramp.

That model Sequoia should have four oxygen sensors. There will be two in each exhaust line. One will be in front of the catalytic converter, and one will be behind it.

B1 should mean bank one. This is the driver side. S1 is probably the oxygen sensor located before the catalytic converter; however, I am not certain of the number sequence here.

The sensors screw into the exhaust pipe. They will have wires coming out the top.

Visit the on-line store, known as reliable-store, they have the repair manuals. I'm sure you will get the solution of your problem.
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