04 CEL for cat.
#11
11-01-2014, 10:49 PM
The rear O2 sensor works in conjunction with the front O2 sensor. If the voltage signal of the rear exceeds parameters and gets close to the voltage signal of the front O2 sensor it triggers the CEL. This will affect the performance of the car because the PCM forces the engine to run in open loop mode. Then the PCM calculates the air/fuel mixture off of preset tables in the PCM and off the MAF and coolant readings. The O2 sensors are ignored. Since the engine is running in open loop mode it runs the engine rich and your mileage will drop. Also, the engine will not perform optimal.
For most cars yes, but not for his. The rear 02 sensor on series II's do not affect performance. It only checks to see if the cat is working properly.
#12
11-01-2014, 11:07 PM
Join Date: Jan 2008
Location: Mountains of Utah
Posts: 4,903
I have my factory exhaust pipe with cat still attached. It has about 65,000 miles on it. Removed it about 6 years ago, been sitting in my rafters, getting ready to take a bunch of parts for scrap. You can have this if you just pay the shipping costs. From my 2002 3.8 n/a engine at the time
#13
11-03-2014, 10:40 AM
I must respectfully disagree. The CEL for the cat is triggered when the voltage signal (altered by the oxygen content of the exhaust) between the front and rear O2 sensors are close to being the same. In order for the PCM to compare the oxygen content the front and rear O2 sensors must work in conjunction with each other. The CEL for the cat can also be triggered by a faulty O2 sensor. That is why a query (codes retrieved from PCM) is done to determine whether it is a bad cat or a bad sensor.
#14
11-09-2014, 06:18 PM
I must respectfully disagree. The CEL for the cat is triggered when the voltage signal (altered by the oxygen content of the exhaust) between the front and rear O2 sensors are close to being the same. In order for the PCM to compare the oxygen content the front and rear O2 sensors must work in conjunction with each other. The CEL for the cat can also be triggered by a faulty O2 sensor. That is why a query (codes retrieved from PCM) is done to determine whether it is a bad cat or a bad sensor.
The u bend o2 does not affect afr, that is the job of the first one. The second one is there to monitor it. It will likely throw a CEL but the motor will NOT go into a closed loop. Other cars, yes.
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