Primary and Secondary 02
05-31-2011, 10:44 AM
#1
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Primary and Secondary 02
I noticed the primary and secondary O2 sensors are different part numbers on majestic honda but what are the real differences?
Who is the OEM MFGR for them? I read somewhere it was NTK/NGK is this true?
Who is the OEM MFGR for them? I read somewhere it was NTK/NGK is this true?
05-31-2011, 11:57 AM
#2
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OEM sensor is made by NTK of Japan.
They have different resistances.
The FRONT o2 (also know as primary, pre-cat, sensor 1, or upstream) produces a voltage. It is relavant to the oxygen content in the exhaust for the ECU to adjust the fuel trim/supply.
The REAR o2 (also know as secondary, post-cat, sensor 2, or downstream) also produces a voltage, but its only function is to monitor the operation of the cat (catalytic converter). The ECU compares the action of the rear o2 (which is small because of the cat action) with the front o2 to determine if the cat is working.
If the action of the 2 o2 sensors are the same, the ECU can say that the cat is not working and set a code P0420 for inefficient cat. This is what happens when you put a test pipe in. The readings become the same.
They have different resistances.
The FRONT o2 (also know as primary, pre-cat, sensor 1, or upstream) produces a voltage. It is relavant to the oxygen content in the exhaust for the ECU to adjust the fuel trim/supply.
The REAR o2 (also know as secondary, post-cat, sensor 2, or downstream) also produces a voltage, but its only function is to monitor the operation of the cat (catalytic converter). The ECU compares the action of the rear o2 (which is small because of the cat action) with the front o2 to determine if the cat is working.
If the action of the 2 o2 sensors are the same, the ECU can say that the cat is not working and set a code P0420 for inefficient cat. This is what happens when you put a test pipe in. The readings become the same.
05-31-2011, 02:08 PM
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I get a code of P0141 with no cat, which is O2 Sensor Heater Circuit Malfunction (Bank 1, Sensor 2). Now my case may be slightly different since I have had no cat for a while and may have damaged the sensor. But I think it is somewhat common that people with test pipes get the P0141 code, but I have certainly heard of the p0420 code for the same situation, and the P0420 code makes more sense.
Edit: My statements were made as a question to Billman, not as a statement of fact. I was hoping for some additional clarification.
Edit: My statements were made as a question to Billman, not as a statement of fact. I was hoping for some additional clarification.
05-31-2011, 02:11 PM
#4
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Gotcha, would this one work as the primary?
http://cgi.ebay.com/ebaymotors/NGK-N...Q5fAccessories
I have a spare O2 sensor sitting around that came out of the CAT but by the sound of it, I can not use this as a primary?
Seems that is the secondary O2 sensor, are the denso brands any good?
http://cgi.ebay.com/ebaymotors/NGK-N...Q5fAccessories
I have a spare O2 sensor sitting around that came out of the CAT but by the sound of it, I can not use this as a primary?
Seems that is the secondary O2 sensor, are the denso brands any good?
05-31-2011, 08:05 PM
#5
Moderator
A P0141 has nothing to do with a testpipe....sorta 
A catless car cannot set a P0141 for lack of catalyst.
However...anyone who gets a P0141 with a testpipe broke the sensor, by heat, or beating on it, or twisting the wires. they are super delicate.
If you have a P0141, there is a 99% chance the o2 is damaged and needs to be replaced.
The other 1% has wiring issues up to the ECU or a bad ECU.
I am on the original o2 in my car. My test pipe has been in for 100k.
A catless car cannot set a P0141 for lack of catalyst.However...anyone who gets a P0141 with a testpipe broke the sensor, by heat, or beating on it, or twisting the wires. they are super delicate.
If you have a P0141, there is a 99% chance the o2 is damaged and needs to be replaced.
The other 1% has wiring issues up to the ECU or a bad ECU.
I am on the original o2 in my car. My test pipe has been in for 100k.
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