[kmorton1988]

Hello everyone!

The models are hard to follow, so forgive me if this is in the wrong forum.

In any case, I have an O2 Sensor concern.

Here's the code and description:

P2251 O2 Sensor Negative Current Control Circuit/Open Bank 1 Sensor 1

This is coupled with some strange (maybe? I suppose I don't have anything to compare this to) voltage readings.

I read the live data from the OBDII port using a Foxwell NT510, which showed the following results:

Upstream (Exhaust Manifold): 3.01v ~ 3.11v, consistent, no major fluctuations outside of this.

Downstream (Under the car, right by the oil pan): .1v ~ .7v, but with sporadic drops to 0.00v for anywhere from 1-10 seconds at a time.

This is confusing to me because the code seems to be stating that the upstream sensor is having voltage issues, but, if I am to believe that the voltage reading shouldn't ever be actual zero during normal operation, then something seems off. Why is the problem code referencing the upstream, when it seems to be at least consistent?

Yesterday, I replaced the downstream sensor with a non-OEM, but not the least-expensive, actual-fit replacement (no splicing, proper connector, same overall appearance). The code and check engine light disappeared for the 25-minute drive home but returned when I commuted to work the next morning before I even left the apartment complex.

I've attached a graph showing the seemingly irregular, inconsistent, sporadic drops to zero read by the downstream sensor.

note the last solid section with zero drops to zero was me idling in a parking lot, no car movement.

My thoughts are that I have a short somewhere between the downstream o2 sensor harness and...well...wherever it goes. However, it is also concerning that the problem code references the upstream sensor.

So, I ask you, fellow Kia enthusiasts and specialists, am I looking at a short, or is it potentially something different? I have a replacement Upstream sensor due to arrive on Friday, just to make sure I'm covering all bases.

 

[kiaguy002]

Although I don't have any hands-on experience with that code and have never seen it reported on an auto forum, the doc is specifically saying there's a problem with the upstream O2 sensor ground circuit. So that's what you need to test.

 

[kmorton1988]

...the doc is specifically saying there's a problem with the upstream O2 sensor ground circuit. So that's what you need to test.

Okay. It’s so strange to me.

Do you happen to know where the upstream sensor voltage range should land? Is the ~3 volts within normal range?

 

[kiaguy002]

... Do you happen to know where the upstream sensor voltage range should land? Is the ~3 volts within normal range?

Standard O2 voltages are always less than 1V, but I've read (again no first hand experience) that some wideband O2 sensors can produce up to 4V. Don't know if your vehicle has that type of sensor, but I suspect that you're seeing the higher voltages as a result of the ground circuit issue. Just a guess on that, so testing is needed to find out what the actual problem is.

 

[kmorton1988]

...that some wideband O2 sensors can produce up to 4V. Don't know if your vehicle has that type of sensor,

Based on virtually all research I've done thus far, it's a 6-wire wide-band lambda oxygen sensor.

Here's a quick image of what the connector looks like:

So I'm not 100% certain if that means that I can indeed see voltages in the 3.0 ~3.1 range, and I've thus far been completely unsuccessful in finding any information about the upstream voltage expectations at all.

And you're right. I plan to check the grounds on both Upstream and Downstream sensors when I go to replace the Downstream sensor this weekend.

 

[DavesSpectra]

The downstream sensor (after warmup,closed loop) should not fluctuate and stay around 700mv... With it wildly fluctuating it looks like you have the primary catalytic converter that's not functioning...
The primary O2 sensor reads the air/fuel mixture and adjusts the mix...
This is constantly swinging in voltage but your primary O2 sensor is barely moving... Your secondary (downstream) O2 sensor like I said should be pretty steady at around 700mv... The secondary O2 sensor is only used to monitor the health of the primary catalytic converter...
So looks like you have a bad primary (Upstream) sensor (not swinging +/-) as it should... and...

you ALSO have either bad a exhaust pipe (rusted out), a bad flex pipe (common), or a bad primary catalytic converter (located in the exhaust header) causing the major swings in the secondary O2 sensor...

Check the flex pipe and the exhaust pipes FIRST....
Dave

 

[Lou O.]

Here is some info I pulled from the web. Hope it helps.
I for sure learned a thing or two!!
Good luck!

Wideband O2 Sensors and Air/Fuel (A/F) Sensors
by Larry Carley copyright 2019 AA1Car.com

Wideband Oxygen sensors (which may also be called Wide Range Air Fuel (WRAF) sensors) and Air/Fuel (A/F) Sensors, are replacing conventional oxygen sensors in many late model vehicles. A wideband O2 sensor or A/F sensor is essentially a smarter oxygen sensor with some additional internal circuitry that allows it to precisely determine the exact air/fuel ratio of the engine. Like an ordinary oxygen sensor, it reacts to changing oxygen levels in the exhaust. But unlike an ordinary oxygen sensor, the output signal from a wideband O2 sensor or A/F sensor does not change abruptly when the air/fuel mixture goes rich or lean. This makes it better suited to today's low emission engines, and also for tuning performance engines. Oxygen Sensor Outputs An ordinary oxygen sensor is really more of a rich/lean indicator because its output voltage jumps up to 0.8 to 0.9 volts when the air/fuel mixture is rich, and drops to 0.3 volts or less when the air/fuel mixture is lean. By comparison, a wideband O2 sensor or A/F sensor provides a gradually changing current signal that corresponds to the exact air/fuel ratio. Another difference is that the sensor's output voltage is converted by its internal circuitry into a variable current signal that can travel in one of two directions (positive or negative). The current signal gradually increases in the positive direction when the air/fuel mixture becomes leaner. At the "stoichiometric" point when the air/fuel mixture is perfectly balanced (14.7 to 1), which is also referred to as "Lambda", the current flow from the sensor stops and there is no current flow in either direction. And when the air/fuel ratio becomes progressively richer, the current reverses course and flows in the negative direction. The PCM sends a control reference voltage (typically 3.3 volts on Toyota A/F sensor applications, 2.6 volts on Bosch and GM wideband sensors) to the sensor through one pair of wires, and monitors the sensor's output current through a second set of wires. The sensor's output signal is then processed by the PCM, and can be read on a scan tool as the air/fuel ratio, a fuel trim value and/or a voltage value depending on the application and the display capabilities of the scan tool. For applications that display a voltage value, anything less than the reference voltage indicate a rich air/fuel ratio while voltages above the reference voltage indicates a lean air/fuel ratio. On some of the early Toyota OBD II applications, the PCM converts the A/F sensor voltage to look like that of an ordinary oxygen sensor (this was done to comply with the display requirements of early OBD II regulations). How a Wideband O2 Sensor Works Internally, wideband O2 sensors and A/F sensors appear to be similar to conventional zirconia planar oxygen sensors. There is a flat ceramic strip inside the protective metal nose cone on the end of the sensor. The ceramic strip is actually a dual sensing element that combines a "Nerst effect" oxygen pump and "diffusion gap" with the oxygen sensing element. All three are laminated on the same strip of ceramic. Exhaust gas enters the sensor through vents or holes in the metal shroud over the tip of the sensor and reacts with the dual sensor element. Oxygen diffuses through the ceramic substrate on the sensor element. The reaction causes the Nerst cell to generate a voltage just like an ordinary oxygen sensor. The oxygen pump compares the change in voltage to the control voltage from the PCM, and balances one against the other to maintain an internal oxygen balance. This alters the current flow through the sensor creating a positive or negative current signal that indicates the exact air/fuel ratio of the engine. The current flow is not much, usually only about 0.020 amps or less. The PCM then converts the sensor's analog current output into a voltage signal that can then be read on your scan tool. What's the difference between a wideband O2 sensor and an A/F sensor? Wideband 2 sensors typically have 5 wires while most A/F sensors have 4 wires. O2 SENSOR HEATER CIRCUIT Like ordinary oxygen sensors, wideband O2 sensors and A/F sensors also have an internal heater circuit to help them reach operating temperature quickly. To work properly, wideband and A/F sensors require a higher operating temperature: 1292 to 1472 degrees F versus about 600 degrees F for ordinary oxygen sensors. Consequently, if the heater circuit fails, the sensor may not put out a reliable signal. The heater circuit is energized through a relay, which turns on when the engine is cranked and the fuel injection relay is energized. The heater circuit can pull up to 8 amps on some engines, and is usually pulse width modulated (PWM) to vary the amount of heat depending on engine temperature (this also prevents the heater from getting too hot and burning out). When the engine is cold, the duty ratio (on time) of the heater circuit will be higher than when the engine is hot. A failure in the heater circuit will usually turn on the Malfunction Indicator Lamp (MIL) and set a P0125 diagnostic trouble code (DTC). Oxygen Sensor Problems Like ordinary oxygen sensors, wideband O2 sensors and A/F sensors are vulnerable to contamination and aging. They can become sluggish and slow to respond to changes in the air/fuel mixture as contaminants build up on the sensor element. Contaminants include phosphorus from motor oil (from worn valve guides and rings), silicates from antifreeze (leaky head gasket or intake gaskets, or cracks in the combustion chamber that leak coolant), and even sulfur and other additives in gasoline. The sensors are designed to last upwards of 150,000 miles but may not go the distance if the engine burns oil, develops an internal coolant leak or gets some bad gas. Wideband 2 sensors and A/F sensors can also be fooled by air leaks in the exhaust system (leaky exhaust manifold gaskets) or compression problems (such as leaky or burned exhaust valves) that allow unburned air to pass through the engine and enter the exhaust.

 

[kmorton1988]

The downstream sensor (after warmup, closed loop) should not fluctuate and stay around 700mv... With it wildly fluctuating it looks like you have the primary catalytic converter that's not functioning...

Even though the downstream sensor is potentially going to read a fluctuating amount of O2 as the engine revs up? I had thought it was normal for any traditional O2 sensor to fluctuate as the engine revved up while it was waiting for the ECM to adjust the air/fuel mixture. Even if it's after the CAT, the CAT, when working correctly, should have a consistent rate at which is reduces the non-oxygen content, thus potentially leaving a consistent ratio, but not necessarily a consistent voltage?

Also, with the downstream sensor readings dropping to zero like that sporadically when the car is in motion, but being able to actually stay consistent when not in motion, does that at all seem like a concern or is it just circumstantial at this point?

This is constantly swinging in voltage but your primary O2 sensor is barely moving...
So looks like you have a bad primary (Upstream) sensor (not swinging +/-) as it should... and...

Even though it's a wideband sensor?

you ALSO have either bad a exhaust pipe (rusted out), a bad flex pipe (common), or a bad primary catalytic converter (located in the exhaust header) causing the major swings in the secondary O2 sensor...

Check the flex pipe and the exhaust pipes FIRST....
Dave

Thank you for your response! I've seen you post a lot around the forum as I was doing my pre-post research and you definitely seem to have been able to help a lot of people with their Kia problems. I'm grateful that you were able to reply here.

When you get a chance, can you take a look at Lou's reply? I'm not so sure anymore that the Upstream O2 sensor should fluctuate as wildly as a standard one would, based on how it works after reading the quoted text he referenced.

Here is some info I pulled from the web. Hope it helps.
I for sure learned a thing or two!!
Good luck!

Wideband O2 Sensors and Air/Fuel (A/F) Sensors
...

Thank you! That gave some decent insight, indeed! So it seems that because it's a Wideband sensor, it is not prone to fluctuation near as much as your standard O2 sensor might be, is that correct? So perhaps my upstream sensor is working properly?

 

[kmorton1988]

Alright, I have some updated info, as I was able to change the upstream lambda/O2 sensor. First, here's some charts that represent the Voltage readings of the Downstream sensor reading and the Upstream sensor.

Upstream:

Downstream:

So, for now, it would seem that DaveSpectra was correct in that the Upstream sensor was indeed bad.

Here are a couple of interesting points:

1. The Upstream sensor, I believe, had a short or a bad wire, because a new reading became available after the update: Lambda Sensor Ratio.

2. The readings off of the old Upstream sensor was in fact over, but not by as much as we thought: the Lambda sensor puts out a reading based on its ratio, not based on the O2 detected, so on average, I should be seeing between 1.1 and 2.0 during normal temps and operating.

The codes were cleared and so far (20 miles and 3 separate trips later) the CEL hasn't come back. I'll return to update if it ends up coming back.

 

[DavesSpectra]

Your down stream O2 sensor should not be swinging wildly like you are showing... This is indicating the primary cat (built into the exhaust header) is not working correctly... The downstream O2 sensor should be pretty close to 700mv and pretty steady with little fluctuation... I have had a 2006, a 2007, two 2008 Spectras... and they all work like I said... If you live in a state where emissions are checked the car won't pass... If there is no checks your replacing the primary O2 sensor will give you good performance and mileage... until the primary Cat fails and gets plugged causing back pressure above 3 PSI...
You said "the Lambda sensor puts out a reading based on its ratio" ... it's of the air/fuel mixture creating more or less hydrocarbons and the ECM adjusts the air/fuel up and down continuously... the cat if working correctly will even out the hydrocarbons and that's why the secondary O2 sensor should read pretty much a continuous reading...