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11

Lambda sensors, often referred to as oxygen sensors or O2 sensors, are the bedrock of any modern-day EFI system. Without them, fuel injection management is essentially flying blind and has to resort to other less-desirable means to determine how much air and fuel need to be mixed. Their primary role is to provide feedback to the fuel management to determine ...


7

This requires a bit of mechanical know-how and some time... An O2 sensor can be tested with a multimeter that measures millivolts. You'll need to securely attach one lead to the signal wire of the sensor and the other to a good ground on the car. This all has to stay in place with the car running... Fire up the engine and look at the voltage reading of ...


7

We found at least two issues The air filter housing wasn't forming a proper seal with the MAF sensor This engine boasts a quirky design where the MAF sensor sits at the back of the engine. The air filter housing seal is in the middle of this first picture, MAF sensor in the second picture (stills were taken from this video). Whoever had installed it ...


6

Your data logs tell me the following: Fuel trims are fine Here are some plots I generated from your data for both short-term and long-term fuel trims. The plot above (Bank 1 STFT vs Bank 2 STFT) show that there is no bank imbalance and most of the data points hover around zero STFT correction, which tells me that feedback from the O2 sensors is ...


5

Check fuse 21 in the under hood fuse box. If the fuse is OK at one of the o2 sensors check for power on the red/yellow wire. If you have no power at the o2 sensor I'm afraid your going to be looking for a short to ground. Which would involve tracing the wiring harness and visually inspecting for rub through or broken wiring.


5

You may want to review this answer of mine. The tests outlined there for heater resistor continuity and response to lean/rich conditions assume a fully functional sensor. If the behavior under testing doesn't match what is outlined there, you know that the sensor has an issue.


5

It is most likely that this sensor has failed. The question is why does the MIL only come on above 70mph. The answer lies not in the sensor but how and when the sensor is tested by the PCM. Every sensor (and actuator) in the engine control system is tested by the software, but not all the time. Each sensor has its own set of test entry conditions; each OEM ...


5

In the perfect world, you just slide a wrench on the O2 sensor and it comes out. Unfortunately since its located in a "hostile" environment (lots of heat, lots of water and potential corrosion underneath) it typically gets pretty stuck, though most people eventually do have success getting it off. Careful not to start stripping it with that open ended ...


5

Just to add to the other answer as I ran into this same issue, what kind of emissions do I have on my mitsubishi galant? I had this code: P0421 and I had to replace my O2 Sensor & the catalytic converter but I wasn't sure if I needed the CARB (California Air Resource Board) compliant ones or not. There is a label that identifies what type you have. I ...


4

Root Cause: probably a couple of things Sadly, I feel that there isn't enough data here to uncover the smoking gun, but I have realized some things upon reflection that can indicate what is probably wrong with the vehicle: Question 1 If the front lambda sensor voltage is indicating rich, why is the fuel trim positive (indicating that the injector ...


4

The upstream o2 on a Prius is an AFR sensor stoich reading at idle is 3.33 volts. The application isn't able to read the correct PID. So of course it would read 0v all the time.


4

Bad O2 sensors can contribute extra heat to the system, but usually they have the opposite effect. When the ECU detects that the sensors are faulty, the engine will default to open-loop mode, which should cause a properly functioning engine to run a rich A/F ratio. This actually has the effect of cooling the combustion charge and removing more heat from ...


4

The Red/Yellow wire is in the harness, not on the O2 sensor. It's can only be something that effects all 4 sensors. The ground is provided individually for each sensor by the PCM so it can't be on the ground side. Power is provided by Fuse 21, but that also powers the EVAP canister vent valve so if that fuse was blown it would also set an EVAP code, but ...


4

TLDR: The sensor is difficult to check because the current change it produces is too small for most clamp meters, so you would have to cut the harness to test it. Not recommended. Try checking for bad connections first. If it's not those, and it's likely not the ECM as you would likely have other symptoms than just this, then try replacing the sensor itself. ...


4

Excellent graphs. The after catalyst sensor shows normal mixture readings. The PCM can and will operate the system lean or rich depending on operating conditions. The voltage will rarely be held at any intermediate voltage, such as 0.5 volt. This is an urban legend not based on engineering fact. The rear sensor voltage should remain steady at any steady ...


3

Hard to say with the information given. Sounds like retarted timing or not enough air or fuel (too rich / lean) . A repair manual will be infinitely useful in testing/troubleshooting. Things to test: codes, even if the CEL isn't on there might be something stored. air filter spark plugs (clean, gapped correctly) wires cap rotor coil vacuum lines (check ...


3

There are currently two kinds of narrowband sensors used these days: titania sensors (NTK) and zirconia (Bosch). This answer only addresses the zirconia sensors which are the most common type. Referring to the diagram (which was created by Michael Handrich and shared under a Creative Commons license), the sensor is a galvanic cell that generates what's ...


3

I haven't been able to find any solid conclusions on the VW forums regarding the root cause for this behavior, but there are some clues as to what could be causing this from the diagnostic code. Fred Wilson's answer remains a distinct possibility but I struggle to reason with why the engine computer would choose to throw a code/MIL for a bad sensor on a ...


3

Lambda sensors have several different failure modes. Heater element. The heater element is a resistive material that resists electron flow thus producing heat. This is the most common cause of early failure. The resistor burns through opening the circuit. Failure of the catalyst material. Usually caused by contaminates coming from the engine. Very ...


3

Also, remember that MAF is a reading of the amount of air entering the engine. If you have a backflow issues (high backpressure) or even a timing issue where the valves are not opening and closing at the correct time (slack chains, jumped timing), your MAF sensor readings will reflect this as well. I know this post is late, but any who are looking into this ...


2

Since this is an OBDI vehicle, there will be only one O2 sensor located where the exhaust ports all come together in the exhaust manifold.


2

Just thought I'd bring this in to an answer to allow it to be accepted: This, while not ideal for you in this situation, is to prevent accidental connection to the wrong sensor. This solution is used in any number of applications, on ships, aircraft, even buildings - and in a car you will find many examples. It's one of the reasons I always read the manual ...


2

In a word? Nothing. I mean, a 4-wire O2 is going to be about the same no matter what it's made for. The connector may be different, but the guts are going to be pretty much the same. Unfortunately, you really need to know what works well with your vehicle. For instance, Bosch (from my understanding) originated the O2 sensor. Their product should be above ...


2

This is a normal fuel control pattern especially for idle. O2 switch patterns are not specified to look a certain way but vary greatly. They are the result of a competing set of requirements including; combustion efficiency, catalyst requirements, driver demand and regulatory requirements. The hold lean strategy seen here is a way to hold the mixture ...


2

Your lambda control looks absolutely fine. And consequently I don't think it is the root cause for your rough idle. Here's my reasoning: The web page linked in your question says The O2 sensor must cycle at least once per second I wouldn't take this as a hard limit for a few reasons: the Bosch Fuel Injection & Engine Management book indicates ...


2

After replacing the sensors- did you clear the codes and drive the car on the highway for a while so that the car computer can re-read the cars activity codes? After finding the codes and performing repair, you should clear codes before trying to get another code reading. Try clearing your codes first. No promises here- but this maybe just what you need.


2

@cdunn has all bases covered, but the intermittency and low voltage tells me that the issue is with the ECU receiving signal from the sensor. Some basic circuit continuity testing with a multimeter will help you track down the reason for the lack of signal.


1

I had a similar issue with one of my cars, after poking and prodding it for a couple of days it came down to the butterfly valve in the air intake sticking, if you throw your foot flat to the floor and it can't suck the air in quick enough it won't have the right air to fuel ratio and run awfully. Just remove your air intake and get someone to rev it ...


1

Because this issue is speed dependent, I'm almost certain that it is related to exhaust gas temperature. Paulster2 suggested checking whether the issue happens at a lower gear. However, then the load on the engine is lower, so there are less exhaust gases. It may be the case that the issue does not happen at a lower gear, therefore. But a good idea to check ...


1

The other answers have covered most things, but here are two points that haven't yet been mentioned. Warranty This is usually a function of the supplier rather than the manufacturer, but some places offer a lifetime guarantee. Others offer none. Physical fit How hard could it possibly be to make accurate threads? Apparently pretty hard for some ...



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