What Is the Ohm Reading of an O2 Sensor of a 2003 Toyota Avalon?

Time-saving communication on catching the really tough bug

Portillo is the head technician of Auto Clinic, a country-of-the-art automotive repair facility in Mahopac, Due north.Y. He has been trained by Automotive Technician Preparation Service and is TST certif ed. Portillo's real-world, in-depth diagnostic articles appear in Auto Service Professional person on a regular basis.

Not long ago, Auto Service Professional person covered all of the basics concerning how to diagnose common oxygen and air-fuel sensor codes (see the March/April 2012 issue). This time, we are going to discuss more advanced sensor diagnosis then you can catch those actually tough bug that are not simply a matter of checking the heater circuit and having a specif cation.

Very brief review

Air-fuel and oxygen sensors work in tandem, earlier and after the catalytic converter. The PCM compares the readings in social club to analyze catalytic eff ciency, and whether the vehicle is running rich or lean.

When the air fuel or front oxygen sensor senses a rich fuel mixture in the frazzle, the PCM takes that data and and then tries to practise the contrary to brand a fuel mixture that is perfect (called "Lambda") by sending fuel trims in the opposite management. Air-fuel sensors ref ect a lean status when their voltage increases and a rich condition when their voltage decreases. Oxygen sensors work the opposite manner, with an increase over 450 mV ref ecting a rich fuel

Effigy 1: When the air-fuel sensor detects rich exhaust, it reports this to the PCM which then takes away fuel to make the air-fuel mixture normal. This is why rich exhaust creates negative fuel trim and vice versa. mixture and a decrease below that number a lean fuel mixture (run across Figure 1).

Mail-cat oxygen sensors, when good, feature a steady voltage ordinarily between 500 to 700 mV. If it zigzags, the catalytic converter is highly doubtable.

Quick air-fuel sensor check. Are you convinced the A/F sensor is stuck lean or rich, but don't have the right specif cation? Until advanced milliamp clamps are mainstream where you would be looking for a specif cation of 0 amps (+ or –0.03 mA), you will have to either put a digital multimeter in series hooked upward in the amps port. This is time consuming and putting the meter in series between the wrong wires tin fry the PCM. A improve method is to stick an emissions analyzer in the tailpipe. If the rear oxygen sensor has elevated mV (something in the 800 mV range) and Lambda is rich, you likely accept an A/F sensor stuck lean. An A/F sensor stuck rich

Chart and data courtesy DENSO

The vehicle emission command information label indicates what type of sensor(s) is nowadays (A/FS for air/fuel sensor; and H02S or 02S for oxygen sensor).

Fuel trim control exhaust sensors

The exterior advent of air/fuel sensors and oxygen sensors may exist very similar but that's where the similarity stops. Using a light seedling analogy, the oxygen sensor sends voltage to the engine control unit and acts similar an on/off switch, turning the bulb on and off. The air/ fuel sensor receives voltage from the engine control unit and acts like a dimmer switch, making the seedling brighter/dimmer. They differ in output characteristics, so although they may look alike, the ii sensor types are not interchangeable.

Vehicles equipped with an air/fuel sensor take approximately 0.4 5 constantly applied to the sensor which outputs a electric current that varies in accordance with the oxygen concentration in the exhaust gas. The ECU converts the divergence in output current into voltage, allowing a response that is directly proportional to the present air/fuel ratio in the exhaust system.

The air/fuel sensor operates at a temperature of ane,200 degrees Fahrenheit, which is twice that of an oxygen sensor. Lean mixture indicates higher voltage on the voltmeter. Rich mixture indicates lower voltage on the voltmeter.

In vehicles equipped with an oxygen sensor, the output voltage changes in accordance with the oxygen concentration in the exhaust gas. The ECU uses this output voltage to determine whether the nowadays air/fuel ratio is richer or leaner than the stoichiometric air/fuel ratio (fourteen.seven:1).

Light-off temperature between 572 degrees F and 752 degrees F is needed to quickly warm upward the oxygen sensor. Three- and four-wire oxygen sensors take builtin heaters.

Lean mixture indicates lower voltage on the voltmeter. Rich mixture indicates higher voltage on the voltmeter.

NOTE: For more sensor diagnostic information and your own copy of DENSO's sensor poster, become to http:// www.densoaftermarket. com/posters/.

is much more than rare, but theoretically tin can exist approached in the aforementioned mode (low rear oxygen sensor voltage and lean Lambda).

Tough P003X oxygen sensor codes. Yous get an oxygen sensor code, the repair is almost always an oxygen sensor, correct? Well, if y'all have a code in the P003X (X equaling 1 through nine) range, you should await that the vehicle has the incorrect sensor or a module Figure 2: 2003 Toyota Camry with a P0031. problem. This tin be all-time illustrated in a instance study. We received a call from a local shop well-nigh a 2003 Toyota Camry 2.4L four cylinder 2AZ-FE California emissions vehicle with a foreign P0031 Oxygen Sensor Heater Command Circuit Low B1S1 (come across Figure 2). This is how the story goes:

They get a "heater circuit DTC," probably a different code number, checked the sensor and it had an open circuit. A new sensor from the dealer was ordered and installed into the vehicle, but the lite stayed on. The resistance of the new sensor's heater circuit appeared skilful, and the PCM was duty cycling the heater excursion nicely, which conf rms the integrity of the wiring. The store and all of its mechanics were stumped and decided to put a computer in it.

That'southward where nosotros come in. We were paid to reprogram the keys to the new PCM and when we did the cheque engine light nevertheless went on with the aforementioned code. Now, we had a diagno

fifty-fifty though this particular lawmaking says "oxygen sensor heater circuit," what they are really talking well-nigh is the forepart A/F sensor. By looking at the wiring schematics, this particular air/fuel ratio sensor is a four wire sensor with two signals wires from the PCM which provide voltage to the sensor. One of these wires is -three.0 (White) and the other +three.3(Orange). The tertiary wire is a heater chemical element circuit (Brown/Red) wire and f nally a battery voltage wire (Brown/ White). The Due east.F.I fuse supplies B+ to the E.F.I relay which then supplies bombardment voltage to the A/F sensor heater chemical element when checking the B+ (Dark-brown/White) wire (encounter

Figure 4). Figure 3: The new PCM yet sis on our easily set the aforementioned DTC and turned (see Figure iii). on the Bank check Engine Lite. On this vehicle,

Effigy 4: Here we accept the wiring diagram for the 2003 Toyota Camry's oxygen sensor heater circuit. Highlighting a wiring diagram oft helps us empathise what we are looking at easier.

It is necessary to visually inspect fuses and relays present for voltage drops situations. When nosotros began diagnosing this car, we were getting 12 V central on. We also checked the fuse and relay which all tested good, so obviously that's why nosotros were getting 12 V.

After these checks we pulled out our scan tool to brainstorm looking at PIDs. Nosotros noticed that the signal for the A/F sensor was a steady 3.29 V, which indicates almost a perfect air-fuel mixture as per the Toyota specif cation. Coolant temperature was 120

labscope to check the integrity of the wiring and to run into if the heater circuit was duty cycling properly.

How do nosotros practice this? We check power on the heater circuit from the PCM and at the sensor itself, and look at the difference. A voltage drop betwixt the two tin ref ect a wiring or connectedness upshot, while a lack of duty cycling at the PCM or the sensor itself can assistance us condemn an individual component (run into Figure 6).

Nosotros did this examination by hooking up the labscope to the black/red heater chemical element wire to the air/fuel ratio sensor

command signal duty cycling between 0 to 14 5 on our ATS EScope. There was no voltage drop between the two signals, every bit y'all can see in the picture, ruby and yellow are overlapping each other. After we did this reading, information technology was no wonder why the other shop thought Figure five: Screenshot from the Toyota Techstream. Look for whatever suspect PIDs. it was the PCM. degrees F, STFT 0% and LTFT +2%. The fuel appeared to check out, lending plausibility trims were practically perfect, which fabricated to the theory that the PCM had some sort of sense given the A/F sensor data. Everything internal logic error. As we take but shown, seemed normal, merely our code did not indiwe had checked everything that was related cate the sensor was non working properly. to this heater excursion problem from check

Instead, we had to dig deeper into why the ing powers and grounds, scan tool PIDs and heater excursion was throwing the lawmaking (run across using a labscope. Notwithstanding, all nosotros proved is that

Figure 5). nosotros had a functioning A/F sensor.

There are only 3 possible causes. The And so, our patience paid off. We decided to sensor, the wiring, and the PCM. Being that keep the auto running and let the labscope it had both a new PCM and sensor from practice its thing. Then, all of the sudden, the the dealership, it was time to whip out the heater circuit was non pulsing between 0 Everything and to the PCM E9 connector pin No. Figure 6: The A/F sensor heater circuit being scoped on iv. Then we started upwards the car and the ATS EScope. The yellow waveform is at the heater circuit itself and the red waveform (overlapped by the did our readings. What we found was yellow i, because in that location is no voltage drop on this a adept PCM pulse width modulated circuit) is directly at the PCM's heater-circuit driver.

to 14 V! It was only reading a steady 14 V. a fat height. Who was incorrect, the dealer or So, the check engine light turned on. Worldpac? Can you estimate why? Our advice? Never trust the parts guy.

The machine warmed up and went from open We talked to the other shop'due south foreman to loop to airtight loop! What the other store tell him that he had the wrong sensor and was doing during their diagnosis is that he replied, "No way, information technology'southward from the dealer!" they just stopped later on taking their readWe told him to humor us and bank check to see ings. Since the car was allowed to run a if he had two Camrys in the store in his fiddling longer, we caught this mistake. receipts. Less than 15 minutes later he

Let's take a wait at the scan tool when called me just to let me know that information technology was the car goes off of open loop mode to closed the wrong sensor that they installed in the loop. It shows that at the fuel system No. car! They had a 2005 Toyota Camry that 1 PID is "OLFAULT." That means the engine needed an oxygen sensor on a future appointment computer cannot get into closed loop, so the and plain they grabbed the wrong PCM knows that the heater sensor off the shelf. That'due south why excursion element is not being the P0031 came back when the commanded/grounded; but car was about to enter airtight the PCM is smart enough to loop. compensate for that consequence Equally you tin meet in the picture to maintain its fuel strategy the sensors await totally difeven though the A/F sensor ferent from the outside and is non operating equally designed. surely the insides are differOLFAULT is another term for ent also, even though they are "LIMP-MODE," but for fuel Toyota's Denso sensors. control. Come across Effigy 7. The ane on the

Why would the PCM get into left is the correct A/F sensor this mode and not closed Figure vii: The correct A/F and the one on the correct is loop? It is nearly incommunicable sensor side by side to the incorrect the incorrect one. Notice how the awarding. that ii PCMs would practise the A/F sensor has 4 breather same exact thing and a little likewise coinciholes and the other simply has ii? Also, one dental that when the vehicle wants to get is thicker than the other. to closed loop that the sensor would stop One last tip. Unless you have an ohms duty cycling. So we f gured it had to be the spec, do not be as well sure that what y'all sensor. are reading is a "practiced" heater circuit. The

A brand new sensor?!? The heater excursion right specif cation for this 2003 Toyota element showed 2.8 ohms of resistance, so Camry I4's A/F sensor is one.1 ohms while the circuit itself was good. Simply, if you accept the 2005 Camry'due south sensor is 2.eight ohms (encounter a code in the P00 as opposed to the P01 range for the oxygen sensor, doubtable that something is confusing the estimator.

We went onto Worldpac speed dial to look up the part number and company of the OE sensor for a 2003 Toyota Camry with the same engine with CA emissions.

What we establish was that the A/F sensor listed was different from what was on the machine. Both sensors were Densos, only the OE sensor on Worldpac had iv holes on the bottom and a skinnier top when compared to the one on the automobile. The auto's A/F sensor Figure 8: The specif cation on a 2005 Camry had just ii holes on the bottom and A/F heater circuit in ohms.

Circle 104 on Reader Service Carte du jour

2003 Camry A/F heater circuit in ohms.

The lower the resistance, the higher the amperage, and so this ECM has been programmed to work and command a pulse width on this heater sensor with college amperage, but keep in mind that this reading was tem to go into closed loop.

heater element

After we installed the correct sensor nosotros had our scan tool connected to testify a bespeak. When the engine was in open loop the A/F sensor voltage read three.29 5 with a STFT of 0 percentage and a LTFT of half dozen percent (see Figure x).

The vehicle warmed up and the PCM went into closed loop and non OLFAULT! That ways the vehicle was 100 percent f xed. Nosotros tested the sensor by going WOT.

The A/F sensor signal was at 2.35 V at three,500 RPM (the engine becomes rich considering of fuel being dumped into the cylinders) and and so the PCM tried correcting itself and cut off fuel sending the A/F voltage to 4.16 V before settling back to iii.29 V.

Likewise notice how the short fuel trim was

Effigy nine: The specif cation for a 2003 Camry A/F heater circuit in ohms. under 10% nether load. Figures eight and 9). Figure 8 is the specif cacontrol in closed loop. tion on a 2005 Camry A/F heater excursion in This same test was performed with the ohms and Figure 9 is the specif cation for a wrong sensor, but there wasn't whatsoever alter

taken when the Figure 10. In this Techstream screenshot, the correct A/F sensor allowed the sysThis indicates that the PCM is under fuel was cold because that is when the heater on voltage or fuel trims because the ECM element works harder. The hotter the sensor was under OLFAULT (over again see Figure 5). gets, the higher the resistance and the ECM Perhaps if nosotros were smarter diagnosticians, detects this and adjusts the pulse width nosotros would have realized that this was not signal in club to get the amperage lower. normal operation, just hey, we had to larn The PCM detected something different than the difficult mode. what it was designed to work with and ready At present that we've been through it, you don't the P0031. accept to feel the same grief. ●

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Source: https://issuu.com/10missionsmedia/docs/asp_0213/s/11106998

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