Function of oxygen sensor? - 2003 Mitsubishi Galant

In a vehicle's exhaust system, oxygen sensors play a crucial role in monitoring and adjusting the air-fuel mixture to ensure optimal engine performance and minimize emissions. The 2006 Trailblazer, like many modern vehicles, typically has two oxygen sensors: one located before the catalytic converter (referred to as the upstream sensor) and one after the catalytic converter (referred to as the downstream sensor).
The upstream oxygen sensor monitors the oxygen content in the exhaust gases before they enter the catalytic converter. This information is used by the engine control unit (ECU) to adjust the fuel injection and air intake to achieve the ideal air-fuel ratio for efficient combustion. Failure to replace a faulty upstream oxygen sensor can lead to decreased fuel efficiency, increased emissions, and potential engine performance issues.
The downstream oxygen sensor, located after the catalytic converter, serves a different purpose. Its primary function is to monitor the efficiency of the catalytic converter by measuring the oxygen levels in the exhaust gases after they have passed through the converter. The ECU uses this information to ensure that the catalytic converter is effectively reducing harmful emissions such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx).
While a malfunctioning downstream oxygen sensor may not immediately affect engine performance or fuel efficiency, it is still important to replace it if faulty. A failing downstream sensor can lead to increased emissions and may cause the vehicle to fail emissions tests. Additionally, it can result in damage to the catalytic converter over time, leading to costly repairs.
In summary, while the upstream oxygen sensor is more critical for immediate engine performance and efficiency, the downstream sensor plays a crucial role in monitoring and maintaining the effectiveness of the catalytic converter and ensuring compliance with emissions regulations. Therefore, it is important to replace both oxygen sensors as recommended to ensure proper vehicle operation and minimize environmental impact.

Re: Replacing O2 sensor - Cadillac Forums

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Cadillac DeVille Oxygen Sensor - PartsGeek.com

Oxygen sensors are typically controlled by the computer and have no fuses or relays involved with their function

Check the relays and fuses for the H.E.G.O (heated oxygen sensors) for power and function.

P1148 - Closed Loop Control Function Bank 1
This mean that the closed loop control function for bank 1 does not operate even when vehicle is driving in the specified condition.

The Powertrain Control Module (PCM) or Electronic Control Module(ECM) monitor the function of the Front Oxygen (O2) sensor or Air/Fuel (A/F) sensor by comparing the signal with the Rear O2 sensor.

Symptoms:
- Engine Light ON (or Service Engine Soon Warning Light)

Possible causes:
- Harness or connectors Front Oxygen (O2) sensor or Air/Fuel (A/F) sensor 1 circuit is open or shorted.
- Front Oxygen (O2) sensor or Air/Fuel (A/F) sensor bank 1
- Front Oxygen (O2) sensor or Air/Fuel (A/F) sensor bank 1 heater

Possible solution:
- Repair harness or connector. If repair is needed
- Replaced Front Oxygen (O2) sensor or Air/Fuel (A/F) sensor bank 1


Then, possible causes are faulty harness or connectors to the air fuel ratio sensor, a faulty air fuel ratio sensor (1) or faulty air fuel ratio sensor (1) heater. Most likely yes it is just faulty sensor. Just replace this devices and reset the stored codes.

Keep us updated.

I can add two two extra possible causes: 1) faulty coolant temperature sensor/low coolant/air in coolant. When the engine is started from the cold the ECU enriches the fuel mix to keep the engine idling; this explains why engines idle high (1000 -1200rpm) at start up. As the engine warms up the coolant temperature sensor signals this and the ECU shortens the injection cycle to eventually bring the engine down to a steady idle (700-800rpm). How to check? Most often the coolant sensor is quite separate to the temperature sender, so a correct read-out on the dash board does not necessarily indicate correct sensor function. Using a voltmeter the resistance across the electrical terminals on the sensor can be measured. By removing the device from the car and putting the end of the sensor in a pan of hot water it should be possible to see an immediate change in resistance, it does not matter so much that the resistance goes up or down but that there is a disernable resistance change with change in temperature. Generally high resistance equates to cold temperatures and vice versa. If there is no resistance change commensurate with temperature change then the sensor is at fault. If there is simply no resistance measurable (open circuit) then the sensor is at fault. If the sensor is working correctly check the connector, the wiring and the wiring insulation for faults and possible shorting.

2) faulty oxygen sensor on the exhaust manifold. If the oxygen sensor indicates that there is too much oxygen in the exhaust the ECU will enrich the fuel mix to compensate. How to check? An issue with oxygen sensors is that they steadily lose effectiveness with age and they can under perform for quite a while before they trigger an error code on the ECU. Ensure the connection to the oxygen sensor is robust and clean. As the oxygen sensor only works when hot there is the danger of getting burnt by working on it so a safe approach is to find the electrical connection on the wiring harness remote from the oxygen sensor and to make voltage measurements there. Most garages have systems that can record the amplitude and frequency of the voltage peaks being produced by the oxygen sensor. A less sophisticated means to get some impression of the oxygen sensor function is to use a moving coil galvanometer type voltmeter (analogue needle on dial). Setting the voltage range to 1 volt and by attaching the meter leads across the sensor wires it should be possible to see the rhythmic pulsing and the voltage range of the operating sensor output. If no pulses are seen it could be either a break in the wire or a fault with the sensor itself.

the O2 sensor monitors the presence of oxygen or the lack of oxygen in the exhaust. It sends a signal back top the computer that tells it if the exhaust is rich or lean. The computer than calculates a fuel trim value to either lean the air fuel ratio or richen the air/fuel ratio.

In a nutshell it is one of the sensors that helps the computer decided how much fuel to give to the engine.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

P1133 is the code that tells you that your HO2S (Heated oxygen sensor) is not performing correctly. This can mean that sensor has failed to function correctly at least twice in a row and so the computer will store the data that occured the first time it failed and turn on the Check engine lite. Most likely you need a new Heated oxygen sensor.

You said you changed the O2 sensors, which ones? I do believe that sensor 2 is the Catalyst efficiency monitor, it looks like an O2 but it's function is different. This sensor is behind the Catalytic converter, the O2 is in front. Bank one is the bank that # 1 cylinder is on, so the sensor that is defective is the 2nd sensor back on that sides exhaust pipe.

P0141 - Heated Oxygen Sensor (HO2S) Heater Performance Bank 1 Sensor 2

P0138 - Heated Oxygen Sensor (HO2S) Circuit High Voltage Bank 1 Sensor 2

P0134 means that no activitiy (function) is detected in the sensor. P0135 is an 02 sensor heater malfunction. Basically, it sounds as if your O2 sensor is dead and needs replacement. Being that you state it's the 1,1 sensor, you're talking about the primary, or pre-catalyst, oxygen sensor. This is the one closest to the engine, before the catalytic converter.