In this article, I'll show you how to test the oxygen sensor on your 1.8L, 2.4L Mitsubishi (Chrysler, Dodge) vehicle.
Your vehicle comes equipped with two oxygen sensors. One is called an upstream oxygen sensor, since it's located before the catalytic converter and the other is know as the downstream oxygen sensor and is located after the catalytic converter. This article focuses on the upstream oxygen sensor (O2S11).
To help you navigate this article, here are its main points:
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Sensor De Oxígeno Delantero (2.4L Mitsubishi) (at: autotecnico-online.com).
Important Suggestions And Tips
TIP 1: You'll need to use a scan tool that has Live Data capability for the O2 sensor test I'm gonna' show you in this article.
In case you wondering, you don't need the factory scan tool or an expensive professional technician level scan tool to follow the test procedures in this article (if you don't have a scan tool and you need to buy one, check out my recommendation here: Actron CP9580 Scan Tool Review -at troubleshootmyvehicle.com).
TIP 2: You will not be removing the O2 sensor to test it, since the O2 sensor test is done with it in place and in action as the engine runs.
Symptoms Of A Bad Oxygen Sensor
A failed oxygen sensor doesn't cause major/severe engine performance issues. You'll usually see one of several of the following symptoms:
- Check engine Light is illuminated on your instrument cluster with one of the following Codes:
- P0132: Heated Oxygen Sensor Circuit High Voltage (Sensor 1).
- P0133: Heated Oxygen Sensor Circuit Slow Response (Sensor 1).
- P0134: Heated Oxygen Sensor Circuit No Activity Detected (Sensor 1).
- P0135: Heated Oxygen Sensor Heater Circuit (Sensor 1).
- Bad gas mileage. A malfunctioning, slow, or non-operating oxygen sensor will have a negative impact on your vehicle's fuel consumption.
- Emissions will be higher, which means your vehicle will pollute more.
Oxygen Sensor Trouble Code Basics
If you've been wondering exactly what the heck each diagnostic trouble code means in lay man's terms, below I've added a few words beyond the official description of the code:
P0133: Heated Oxygen Sensor Circuit High Voltage (Sensor 1)
- This tells you that the oxygen sensor before the catalytic converter is reporting a high voltage of 4.5 Volts or more when the engine is in operation.
- When the oxygen sensor's output signal is viewed with a scan tool (in Live Data mode), the scan tool will report 4.5 Volts or higher for O2S11.
- With the help of the oxygen sensor test in this article, you'll be able to confirm if the O2 sensor output voltage is really at 4.5 Volts or higher.
- In my experience, the times I've seen this problem is when the oxygen sensor's wires have melted together and thus shorting to each other or a universal oxygen sensor was used and the wires were not spliced to the correct ones (of the old connector).
P0132: Heated Oxygen Sensor Circuit Slow Response (Sensor 1)
- This tells you that the oxygen sensor before the catalytic converter is switching between a Lean and Rich condition too slowly.
- This diagnostic trouble code (DTC) usually always means that the O2 sensor is old and ready to retire.
- With the help of the oxygen sensor test in this article, you'll be able to confirm if the O2 sensor is worn out and not responding fast enough.
P0134: Heated Oxygen Sensor Circuit No Activity Detected (Sensor 1).
- This tells you that the O2 sensor's output does not cross 0.5 Volts after the engine has warmed up (operating temperature above 169° F [76° C]).
- This most always indicates that the O2 sensor has completely worn out and is dead.
- With the help of the oxygen sensor test in this article, you'll be able to confirm if the O2 sensor has gone on to the 'big gig in the sky'.
P0135: Heated Oxygen Sensor Heater Circuit (Sensor 1).
- This tells you that the PCM has detected the heater inside the O2 sensor has gone bad.
- 99.9% of the time, this indicates that you need a new oxygen sensor (because its internal heater has fried).
Oxygen Sensor Basics
If you're like me, you want to get right into testing the O2 sensor and forget about having to read the working theory of the component, but in this case it's a good idea to learn how the oxygen sensor works so that you can see the ‘how’ and 'why' of the actual test.
The following description (of how the O2 sensor) works is to the point and as brief as possible but without omitting the important stuff you need to know to successfully test upstream oxygen sensor (O2S11).
- The upstream oxygen sensor (O2S11) is tasked with reporting how Rich or Lean the exhaust gas is. This info is sent directly to the PCM. The PCM then uses this info either inject more or less fuel.
- Rich: means that the air/fuel mixture (that's being ignited in the engine) is too fuel heavy. This causes an excess amount of unburned fuel (hydrocarbons) to pass into the exhaust, which cause the O2 sensor to report voltage values above 0.5 Volts.
- Lean : means that the air/fuel mixture is too fuel light. This results in high concentration levels of oxygen to pass into the exhaust gas, which causes the O2 sensor to report Voltages below 0.5 Volts.
- The PCM is constantly adjusting the amount of fuel it's injecting into the engine, which causes the O2 sensor to constantly switch between a Lean and Rich condition.
- So, when the PCM injects too much fuel, the O2 sensor reports voltages above 0.5 Volts (Rich Condition). As soon as the PCM sees this, it injects less fuel.
- As the PCM injects less fuel, it may go too far and not inject enough. The resulting Air/Fuel Mixture (after it gets ignited), causes the O2 sensor to report voltages below 0.5 Volts (Lean Condition). The PCM sees this report and starts to inject more.
- This cycle is repeated constantly several times per so many seconds as the engine runs.
- All of these voltages can be easily observed with a scan tool in Live Data mode and this is how I'm gonna' help you troubleshoot the upstream oxygen sensor on your vehicle.
- When the oxygen sensor (O2S11) fails completely, the oxygen sensor stops reporting the changes in the exhaust and usually stays stuck at some voltage number below 0.5 Volts.
- When the O2 sensor wears out, it does report the changes in the exhaust, but very slowly.
- All of the above malfunctions can be observed with your scan tool.
