Questions and discussions about oxygen (O2) sensors. Oxygen sensors are used to measure the exhaust gas concentration of oxygen for internal combustion engines in automobiles and other vehicles.

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12
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1answer
11k views

Do I have to rely on wire color to correctly wire up an O2 sensor?

It seems that everyone and their grandmother has a different color-code convention for 4-wire O2 sensors, which complicates matters when one is trying to wire up a replacement "universal" O2 sensor. ...
9
votes
1answer
335 views

A most intriguing cold-start misfire mystery

I'm trying to help a friend out with a CEL on his 2009 Merc GLK 280. Hooked it up to an OBD2 reader and retrieved a single code: P0300 - 'Random/Multiple Cylinder Misfire Detected', via the 'OBD ...
11
votes
3answers
70k views

Check Engine code P0420 Catalyst efficiency below threshold bank 1

After months of normal driving with no problems, my 2003 Honda Civic EX check engine light came on during a long trip. Got it scanned and it's P0420: Catalyst efficiency below threshold bank 1. They ...
11
votes
1answer
250 views

How do lambda sensors work?

Virtually every modern passenger vehicle today utilizes lambda sensors from the factory. How critical are they to a vehicle's operation? How do they work?
12
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1answer
104 views

Are widebands known to go lazy over time?

I know narrowbands can go lazy with time, but what about widebands? This is a sequel to the cold-start misfire mystery. It turns out that we were looking at the wrong PID's for the front O2 sensor ...
7
votes
1answer
95 views

Locating the O2 sensors and the cat along the exhaust

I gather that the upstream O2 sensor is the one right in the center of this picture. I also gather that the catalytic converter (the "cat") is the bulbous part of the exhaust right behind this sensor. ...
4
votes
1answer
483 views

Oxygen sensor PID for 2004 Toyota Camry 4-cyl

My 2004 Toyota Camry with 170k miles is pulling a P0420 code, which I've read can be due to a bad catalytic converter or O2 sensors. I have an OBD-II tool with the DashCommand app on my iPhone. ...
4
votes
2answers
195 views

What controls O2 sensor/lambda cycling?

I just replaced the lambda on my 98 Mazda 626 GF 2L because it was showing a signal that was constantly pegged lean and I suspected it was defective. After replacing the sensor I took the car for a ...
3
votes
1answer
3k views

How do I repair the O2 sensor in a 2001 Toyota Camry?

I have a 2001 Toyota Camry and the O2 sensor near the front of the car is bad (this is confirmed by the code that the computer has returned). Though I'm not particularly knowledgable about cars (...