Nissan Frontier: P2A00 Front AFR Code (But Actually The Rear Is Bad)
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Date: 2020-08-05
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Comments and reviews: 10
Steve
On systems with a wideband upstream and narrowband downstream it's a fairly common strategy to use the downstream sensor to trim/adapt/learn the stoichiometric lambda=1 point of the upstream sensor. This is because wideband sensors tend to have bigger uncertainty / drift in measuring the exact lambda 1 point (as well as the PCM's limitations of being able to measure the tiny voltage change between e. g. lambda 1 and 1. 01, so it's useful to compare with the downstream narrowband which has a very precise and easy to detect voltage switch at exactly lambda 1, which you need to run very close to for best cat efficiency. In practice comparing up/downstream is a bit more complicated due to having a cat between them which obviously smooths out the AFR fluctuations, so the PCM is probably doing some kind of long term average of the downstream signal to see if it is offset compared to the upstream(e. g. if upstream is controlling to what it thinks is 50: 50 rich/lean time but downstream sees 60: 40 rich/lean time, or is continuously slightly rich/lean you might judge that the upstream sensor reading is offset rich/lean from true lambda 1 and flag a fault. This of course only works if you're sure the downstream is actually reporting good data! I guess if 2 sensors disagree which one do you blame? If you notice an up/downstream mismatch faster than you notice the downstream not responding/low amplitude, the PCM makes the wrong call, and once it flags an upstream sensor fault it might go open loop/inhibit the downstream diagnostics so it will never detect the stuck downstream signal.
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On systems with a wideband upstream and narrowband downstream it's a fairly common strategy to use the downstream sensor to trim/adapt/learn the stoichiometric lambda=1 point of the upstream sensor. This is because wideband sensors tend to have bigger uncertainty / drift in measuring the exact lambda 1 point (as well as the PCM's limitations of being able to measure the tiny voltage change between e. g. lambda 1 and 1. 01, so it's useful to compare with the downstream narrowband which has a very precise and easy to detect voltage switch at exactly lambda 1, which you need to run very close to for best cat efficiency. In practice comparing up/downstream is a bit more complicated due to having a cat between them which obviously smooths out the AFR fluctuations, so the PCM is probably doing some kind of long term average of the downstream signal to see if it is offset compared to the upstream(e. g. if upstream is controlling to what it thinks is 50: 50 rich/lean time but downstream sees 60: 40 rich/lean time, or is continuously slightly rich/lean you might judge that the upstream sensor reading is offset rich/lean from true lambda 1 and flag a fault. This of course only works if you're sure the downstream is actually reporting good data! I guess if 2 sensors disagree which one do you blame? If you notice an up/downstream mismatch faster than you notice the downstream not responding/low amplitude, the PCM makes the wrong call, and once it flags an upstream sensor fault it might go open loop/inhibit the downstream diagnostics so it will never detect the stuck downstream signal.
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Speeder105
I have a 2005 Nissan 350z. I ran into a similiar issue were I had trouble getting the O2 Sensor and Catalyst Monitors to a ready status. I tried going with the drive cycles a few times and that didn't work. I used the Torque Pro App with a Bluetooth OBDII Wireless Scanner to figure out the culprit of this issue. The car also threw a pending code twice when I performed those driving cycles. It turned out that the Driver Side Rear O2 Sensor was going bad. The way I found out was I looked at the voltage readings for the front and rear O2 Sensors and I noticed that the voltage reading for the driver side rear o2 sensor was stuck at a particular voltage reading regardless of engine load just like in the video with the Nissan Frontier. I ordered a new O2 Sensor and I was able to get all of the monitors to show a ready status.
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I have a 2005 Nissan 350z. I ran into a similiar issue were I had trouble getting the O2 Sensor and Catalyst Monitors to a ready status. I tried going with the drive cycles a few times and that didn't work. I used the Torque Pro App with a Bluetooth OBDII Wireless Scanner to figure out the culprit of this issue. The car also threw a pending code twice when I performed those driving cycles. It turned out that the Driver Side Rear O2 Sensor was going bad. The way I found out was I looked at the voltage readings for the front and rear O2 Sensors and I noticed that the voltage reading for the driver side rear o2 sensor was stuck at a particular voltage reading regardless of engine load just like in the video with the Nissan Frontier. I ordered a new O2 Sensor and I was able to get all of the monitors to show a ready status.
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Shawn
Eric careful on just reving engine to determine if rear 02 is active on a Nissan. The newer ones will not be come active till you drive it a short bit. AFR 1. 5v is accurate for older system. Newer ones are 2. 2v. Some newer Nissan's are running 1. 78v reading on scan tool when koeo. Again needs to be driven to get it active reving is not enough. Also I am seeing a lot of small leaks causing fuel trim codes. Need to pressurize the exhaust system to find. You will not hear it. Nissan uses rear 02 for fuel trim adjustment they don't tell you this but they do it.
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Eric careful on just reving engine to determine if rear 02 is active on a Nissan. The newer ones will not be come active till you drive it a short bit. AFR 1. 5v is accurate for older system. Newer ones are 2. 2v. Some newer Nissan's are running 1. 78v reading on scan tool when koeo. Again needs to be driven to get it active reving is not enough. Also I am seeing a lot of small leaks causing fuel trim codes. Need to pressurize the exhaust system to find. You will not hear it. Nissan uses rear 02 for fuel trim adjustment they don't tell you this but they do it.
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3stro
I got the same code in my 09 370z and it has kept coming back even after changing the bank 1 upstream AFR sensor so I guess now I know I should check my rear O2 sensor. It came on after getting an aftermarket clutch installed so maybe the shop didn't connect the sensor all the way correctly when putting everything back together or maybe the sensor is dead. Just got myself an OBD2 sensor with live data capability so I will also check to see if it behaves like the one in this video.
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I got the same code in my 09 370z and it has kept coming back even after changing the bank 1 upstream AFR sensor so I guess now I know I should check my rear O2 sensor. It came on after getting an aftermarket clutch installed so maybe the shop didn't connect the sensor all the way correctly when putting everything back together or maybe the sensor is dead. Just got myself an OBD2 sensor with live data capability so I will also check to see if it behaves like the one in this video.
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Arno
Nissan has some other strange things as well. For example, even though service information says that the TCM gets engine RPM from the crank sensor, it does not. It comes from the cam sensor. So mid 2000s 3. 5 v6 Nissans with a P0340 cam code can act like a bad trans or TCM. Also if a customer keeps driving with a bad wheel speed sensor one of the solenoids in the HCU can remain energized which burns out the transistor in the module.
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Nissan has some other strange things as well. For example, even though service information says that the TCM gets engine RPM from the crank sensor, it does not. It comes from the cam sensor. So mid 2000s 3. 5 v6 Nissans with a P0340 cam code can act like a bad trans or TCM. Also if a customer keeps driving with a bad wheel speed sensor one of the solenoids in the HCU can remain energized which burns out the transistor in the module.
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Mr
Bad coding for fault logic is the reason, indeed it to do with rear response used in checking front but rear fault logic is awol on these, No heater circuit or rear codes when fully disconnected pretty good clue programming logic bit off.
Most annoying thing is it not in a nissan tsb or fault criteria notes so for sure lot of owners been screwed by a parts canon shop on this one.
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Bad coding for fault logic is the reason, indeed it to do with rear response used in checking front but rear fault logic is awol on these, No heater circuit or rear codes when fully disconnected pretty good clue programming logic bit off.
Most annoying thing is it not in a nissan tsb or fault criteria notes so for sure lot of owners been screwed by a parts canon shop on this one.
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Neal
GST= generic scan tool. A word of caution when working on nissans. The first thing to check when diagnosing any check engine light. Always check to make sure the ecm has been updated to the latest version. Nissan has a lot of updates for ECMs. A lot of codes are repaired without any parts. Remember always check for factory technicial service bulletins before doing any thing else.
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GST= generic scan tool. A word of caution when working on nissans. The first thing to check when diagnosing any check engine light. Always check to make sure the ecm has been updated to the latest version. Nissan has a lot of updates for ECMs. A lot of codes are repaired without any parts. Remember always check for factory technicial service bulletins before doing any thing else.
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Jason
Cat monitor on American cars has no bearing on upstream o2 sensors or as stated AFR air fuel ratio as Nissan does weird. The EPA will love this this shit is years above California emissions standards TODAY. Some little prick will realize this and call for the same ecm control strategy in the American market. Lets just plug them in and dump the gas can. SAD.
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Cat monitor on American cars has no bearing on upstream o2 sensors or as stated AFR air fuel ratio as Nissan does weird. The EPA will love this this shit is years above California emissions standards TODAY. Some little prick will realize this and call for the same ecm control strategy in the American market. Lets just plug them in and dump the gas can. SAD.
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Shared
I can explain. The Nissan engineer responsible for setting that code in the ECU software just flat screwed up. This what you call a bug in the software world but Nissan perhaps isn't worried enough about it to issue a TSB or fix it with an ECU update. You don't usually see these kinds of problems with Honda, Toyota, or Subaru.
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I can explain. The Nissan engineer responsible for setting that code in the ECU software just flat screwed up. This what you call a bug in the software world but Nissan perhaps isn't worried enough about it to issue a TSB or fix it with an ECU update. You don't usually see these kinds of problems with Honda, Toyota, or Subaru.
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Pedro
This is a great video. Thanks for sharing the knowledge, Eric. Not sure if you'll see this anytime soon but I have a 2006 Nissan Pathfinder (4. 0L. Check Engine keeps coming on and my Code reader shows the P2A00. Do u know if the issue with this code applies to my Pathfinder as well? Freaking O2 Sensor (B1S2) is 195.
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This is a great video. Thanks for sharing the knowledge, Eric. Not sure if you'll see this anytime soon but I have a 2006 Nissan Pathfinder (4. 0L. Check Engine keeps coming on and my Code reader shows the P2A00. Do u know if the issue with this code applies to my Pathfinder as well? Freaking O2 Sensor (B1S2) is 195.
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