P0140 is a generic OBDII trouble code. It has the same meaning for any vehicle with OBDII, including the Toyota Tacoma.
It means that the PCM/ECM is not detecting any activity from the sensor. It doesn’t mean that the O2 sensor isn’t getting power, but that the voltage isn’t changing, which is the “no activity”.
Bank 1 indicates that the sensor is on the side of the engine with cylinder 1 in the firing order. Sensor 2 monitors emissions after the catalytic converter. It’s usually the Oxygen Sensor located directly after the converter.
Look up which side of the engine bank 1 is on
If it’s an inline engine (almost all 4 cylinder motors), you don’t need to worry about which side it’s on, since there’s only one exhaust manifold.
P0140 Definition
P0140: O2 Sensor → No Activity Detected →Bank 1 Sensor 2
The Tacoma’s computer uses the oxygen sensor to measure the amount of O2 gases in the exhaust. It uses this data to tune the engine on the fly.
When there is no signal from this oxygen sensor, the engine will not be able to run at optimal efficiency, and you’ll get that annoying check engine light.
The PCM supplies a voltage or roughly .45v to the O2 sensor. As the engine warms up, this voltage is supposed to change. If it doesn’t (or does so too slowly) the P0140 code will be thrown.
This video is extremely helpful in going about how to test P0140:
P0140 Symptoms Toyota Tacoma
Most of the time, the only symptom of P0140 is going to be the service engine soon light. This is due to the fact that sensor 2 monitors exhaust emissions.
Toyota Tacoma P0140 Causes
There are a lot of different things that can cause P0140 to be thrown in the Tacoma. Here is a list of common potential causes for P0140 in general:
- Wiring– You’ll want to visually inspect the harness where it plugs into the O2 sensor. Make sure that the pins look good and that the harness is seating well and not cracked. Also check to make sure that the wiring is not frayed or shorted. How to check for a short (YouTube).
- Bad O2 Sensor– The oxygen sensor itself can go bad. This is often the cause of P0140. Replacing it without testing the wiring going to/from it first is a gamble that will often pay off, but it’s still a good idea to check your harness connections and inspect it first.
- Exhaust Leak– An exhaust will can cause P0140. You should be able to listen and find it.
- Bad Heated O2 Circuit
The wiring harness often goes bad with the 02 sensor by the catalytic converter. The extreme heat from the exhaust can really damage a wiring harness, espescially the connection.
Conclusion
There are a lot of issues that can cause P0140 in the Toyota Tacoma. Most of the time, it’ll be the O2 sensor or the wiring to it. If you feel there is anything that you could do to improve or add to this article, please leave a comment below.