Gen 3 Prius O2 Upstream Sensor Readings
| http://world wide web.4x4wire.com/toyota/4Runner/tech/OBDII_ECU/ | Short Cuts |
By: Dan Eddleman - May 2005
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| Check Engine Low-cal |
Is it time to supplant the O2 Sensor on your 3rd generation Toyota with the 3.4L V-6 or two.7L four cylinder engine? In this case the trusty "Check Engine" light may not be the best guide to tell you when this is necessary. I had noticed that my gas mileage had consistently dropped at least x% or, about 2 mpg, without the usual explanation of winter oxygenated gasoline or any other symptoms. The Check Engine light had not come up on, and I couldn't see whatsoever changes on the O2 Sensor voltage swing pattern using my OBDII scanner. So how does 1 know when it'due south time to supersede this rather expensive sensor?
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| O2 Sensor Output, Engine Idling |
If y'all are not familiar with the OBDII (On Board Diagnostic generation Ii) systems used on 3rd generation and subsequently Toyotas, you might want to read this reference before proceeding further in this commodity. Every bit described in the reference article, the oxygen sensor in the exhaust arrangement is the key "feedback" sensor for correcting and maintaining the proper fuel mixture. It measures the post-combustion gases to determine the actual air/fuel mixture of the prior combustion cycle and then, the ECU adjusts the fuel trim percent on the next combustion bike, to keep the fuel mixture at the optimum value.
As the oxygen sensor ages, its responsiveness begins to slow downward. Since I have a BR-3 OBD-II scanner that tin read the voltages generated by the O2 sensor, I idea I would be able to see some indication in the voltage bespeak that my O2 sensor was not providing optimum performance. Even so when I examined the O2 Sensor Output with the engine idling, it appeared to be pretty much the same as I had seen when the vehicle was new. Also, the error codes applicable to the O2 Sensor had not shown upwardly and turned on the Check Engine light.
However, if the Check Engine Light were to turn on with one of the post-obit O2 Sensor codes stored, yous should follow the diagnostic procedure and supervene upon the O2 sensor if so indicated in the diagnostic procedure.
| Oxygen Sensor Fault Code Summary | ||
| Code | Detected Status | Trouble Area |
| P0130 | Oxygen Sensor Circuit Malfunction(Bank 1 Sensor ane) Voltage output of heated oxygen sensor remains at 0.4V or more, or 0.55V or less, during idling subsequently engine is warmed upwardly (two trip detection logic) |
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| P0133 | Oxygen Sensor Excursion Ho-hum Response(Bank 1 Sensor one) Response time for heated oxygen sensor's voltage output to change from rich to lean, or from lean to rich, is 1 second or more during idling subsequently engine is warmed up. (2 trip detection logic) |
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| P0135 | Oxygen Sensor Heater Circuit Malfunction(Banking company 1 Sensor ane) When oxygen sensor heater operates, heater electric current exceeds 2.35amps (2 trip detection logic) |
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| P0141 | Oxygen Sensor Heater Circuit Malfunction(Bank 1 Sensor 2) When oxygen sensor heater operates, heater current exceeds 2.35amps (ii trip detection logic) |
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After doing some all-encompassing reading, it began to come clear how the O2 Sensor performance could be off, even so non be able to run across whatsoever symptoms (other than lower gas mileage) with the tools I was using. Information technology turns out that the O2 swing wheel shown in the photographs is the swing time of the overall system and not just the O2 sensor itself. To really examine the functioning the O2 sensor, for instance to determine if information technology was developing a lean or rich offset, one would have to use a digital volt meter with an averaging feature connected direct to the sensor and look for the 450mV centerline point in a known, properly performing system centered at the 50% duty bicycle. To measure responsiveness, i would accept to use a laboratory scope and setup specifically for this measurement equally a properly performing O2 sensor has response times in the neighborhood of a few hundreds of a second, not the average 1.8 seconds seen every bit the overall organisation response time past an OBDII scanner.
So when do you supplant the O2 sensor? The reply turns out to be simple. Per a trusted Toyota service managing director'south experience and, experiences posted in the Toyota 4x4wire Forum, the O2 sensor needs to be replaced on boilerplate every 75,000 miles to maintain optimum gas mileage performance.
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| The Replacement Oxygen Sensor |
Replacing the O2 Sensor is a relatively simple process. Shown on the left is the new O2 Sensor that I purchased for $138.00 plus tax. The office number shown in the photo on the left is for a non California spec vehicle, which uses for Sensor 1, a narrow range oxygen sensor, simply called the oxygen sensor. The sensor 1 used on a California spec vehicle is a wide range oxygen sensor, chosen an air/fuel ratio (A/F) sensor. So when buying the replacement part, make certain y'all are specify your vehicle is a California spec or non California spec vehicle to get the right role.
There are 2 sensors on your vehicle. Sensor ane is located in front of the catalytic converter. Sensor 2 will be located behind the first and only catalytic converter on a non-California spec vehicle and backside the second catalytic converter on a California spec vehicle. Sensor i is the one that affects gas mileage as its condition degrades. Sensor ii is there to monitor the condition of the catalytic converters and does not need to exist replaced to correct the lower gas mileage problem.
The first photo beneath shows the location of Sensor 1, in forepart of the catalytic converter on the exhaust organisation, just to the right the transmission.
It turns out that disconnecting the Sensor ane plug from it's mating connector is the difficult function of this job. This is a latched connector and if you simply try to pull the plugs apart, you lot either won't succeed, or volition harm the wiring in the process. I showtime tried using one of the thin gauges from an old ignition point gauge set to push open the latch to disconnect the O2 plug. This was not successful primarily because I could non see the connector well enough equally shown in the second photo below. It will be much easier if you lot outset remove the commodities belongings the connector bracket in place equally shown in the third photo so you can swing the plug down for easier access. Then, y'all will exist able to see much meliorate the plug servant latch. As presently as you accept correctly moved the retainer latch away from the plug trunk, the plug should very easily pull out of the connector as shown in the concluding photo on the right.
With the Sensor one plug disconnected, it is at present a simple affair to use a 12mm box end wrench to remove the two bolts holding the sensor 1 and gasket on the exhaust system. Remove the two 12mm nuts equally shown below and install the new Sensor 1 and gasket. The torque specs on the 12mm nuts is 14 pes-lbs, which is about the aforementioned torque used to install spark plugs.
The installation is now complete. I did take one additional stride to make clean the Sensor 1 contacts using electric contact cleaner before inserting the plug into the electrical connector. I am somewhat surprised that this critical connector is non an o-ring sealed connector similar to those used under hood for critical engine connections. If you lot like to off route in deep water or mud, this is something to think about. You should besides consider the fact that the O2 sensor is actually 2 sensing elements, with i ventilated to the exterior to sense ambient oxygen levels for use equally a reference for the second internal element that senses the frazzle gas oxygen level.
At this point, you are ready to kickoff the vehicle and cheque out the operation of the new sensor. I am going to laissez passer along the following experience should y'all run across the same situation. The FSM does not country anything virtually resetting the Principal ECU figurer, nor accept I been able to find out any information indicating that new O2 sensors take a first upwardly or break in catamenia. Merely, the following experience makes me believe information technology might have the O2 sensor longer to fire up and operate the first time.
I started my vehicle with the BR-three scanner attached and watched the new O2 sensor voltage output as the engine warmed up. It seemed that it was taking an abnormal amount of time for the system to go into closed loop and, for the characteristic sine wave swing of the O2 sensor to become evident. And so I decided to take the vehicle on a short drive to really oestrus up the engine and sensor, and with the BR-3 scanner connected. The check engine light came on with a PO125 error indicating that there was insufficient coolant temperature for Closed Loop control. The details of the PO125 error is shown below.
| PO125 Mistake Detail | ||
| Code | Detected Status | Trouble Area |
| P0125 | Insufficient Coolant Temperature for Airtight Loop Operation After the engine is warmed upwards, heated oxygen sensor (bank ane, sensor 1) output does not bespeak RICH (greater than equal to 0.45V) even once when conditions (a), (b), (c) and (d) continue for at least 1.v minutes:
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In essence, (and knowing that all else was in skillful condition), this error says that the Primary ECU was not seeing the O2 sensor characteristic sine wave swing later on waiting 140 seconds which, should have been enough fourth dimension for the signal appear. I kept driving a little further and eventually begin to see the proper O2 voltage swing. I stopped and reset the PO125 error and have had no further problems. So this tells me there may be a longer get-go fourth dimension heat upward period for the O2 sensor to begin generating the expected indicate. If anyone else has had any experience regarding this, I would capeesh you dropping me a line at the e-mail address at the top of the article.
Lastly, my gas mileage has increased dorsum to what the vehicle was originally getting.
Based on other's experiences with failing gas mileage posted in the 4x4wire Toyota Forums, and a service manager recommendation, the O2 sensor does need to be replaced nearly every 75,000 miles to keep your Toyota running in optimum status. It a fairly unproblematic process to do and something anyone who likes to perform their own maintenance and service tin can practice.
It never hurts to have the Toyota FSM for your vehicle which includes diagnostic procedures, possible causes and additional information on differences between California specification and not-California specification vehicles. Also included are precautions you should observe both for personal safety and to prevent other possible damage to the vehicle.
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Source: http://www.4x4wire.com/toyota/4Runner/tech/O2_Sensor/index.htm.bak
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