Runner4

My CEL light came on yesterday, but the rig seems to be running fine. I am assuming it may be an O2 sensor since I am still on the OEM one and the rig has almost 150K on it. I plan on having AUtozone pull the code, but how can I tell if the O2 sensor is bad?

waskillywabbit

iTrader: (-1)

Most local chain auto parts places will pull codes off the CEL for free.

gwhayduke

Go to Autozone or some other auto parts store and have them pull the codes for you. It may not be the O2 Sensor and you don't want to spend $90+ on fixing the wrong thing. I've had the same sensor in my '95 since I bought it (at 95,000 miles) and I don't really think it's ever been changed in 223,000 miles. It still runs great, passes all emission inspections and gets about 19 mpg in city.

Runner4

If they pull a code, most codes are not very specific. For instance a code may imply an Emissions problem, but it won't literally state that an O2 sensor is bad. I would like to know if there is a way to check to make sure if an O2 sensor is faulty or not. I hope I'm making sense.

NathanBERG

I would guess it is your O2 sensor. It would not hurt to change it. Well it may hurt your wallet. But that thing takes a lot of heat and they do go bad.

ColImport

If your car has lost several miles per gallon of fuel economy and the usual tune up steps do not improve it - this *is not* a pointer to O2 failure, it just brings up the possibility. Vacuum leaks and ignition problems are common fuel economy destroyers. As mentioned by others, the on board computer may also set one of several failure "codes". If the computer has issued a code pertaining to the O2 sensor, the sensor and it's wiring should be tested. Usually when the sensor is bad, the engine will show some loss of power, and will not seem to respond quickly.

Use a high impedence DC voltmeter . Clamp the sensor in a vice, or use a plier or vice-grip to hold it. Clamp your negative voltmeter lead to the case, and the positive to the output wire. Use a propane torch set to high and the inner blue flame tip to heat the fluted or perforated area of the sensor. You should see a DC voltage of at least 0.6 within 20 seconds. If not, most likely cause is open circuit internally or lead fouling. If OK so far, remove from flame. You should see a drop to under 0.1 volt within 4 seconds. If not likely silicone fouled. If still OK, heat for two full minutes and watch for drops in voltage. Sometimes, the internal connections will open up under heat. This is the same a loose wire and is a failure. If the sensor is OK at this point, and will switch from high to low quickly as you move the flame, the sensor is good. Bear in mind that good or bad is relative, with port fuel injection needing faster information than carbureted systems.
ANY O2 sensor that will generate 0.9 volts or more when heated, show 0.1 volts or less within one second of flame removal, AND pass the two minute heat test is good regardless of age. When replacing a sensor, don't miss the opportunity to use the test above on the replacement. This will calibrate your evaluation skills and save you money in the future. There is almost always *no* benefit in replacing an oxygen sensor that will pass the test in the first line of this paragraph.


I did not write that...but good luck

firemedic

The codes are pretty much all emission related, I am almost positive that the codes will tell you if you have an O2 sensor problem, it will also identify problems with TPS, coolant temp sensor, AFM, etc...pretty much any EFI/emissions sensor. The later models (I believe 95/96 and newer) like yours, with OBDII are even more specific than older models like mine.

ColImport

If you find out what code it is I can look up the speciffic meaning to the code

Runner4

Thanks for all your input. I will have the code pulled in the next day or so.

Runner4

Well I went to AutoZone and had the codes pulled. It was code P0133 (Bank 1 O2 Sensor). So it looked like I had a faulty O2 sensor. Later last night I was driving and came to a stop light, and the CEL went off. Don't know what to think of this. Also, why are 4Runner O2 sensors soo much money?? Almost $300 to replace both from AutoZone! Wow - I couldn't believe that price.

gwhayduke

Don't buy them from Autozone, buy from an online Toy dealer. You'll get genuine parts that will plug and play. Google discount Toy parts or try this guy:

https://www.1sttoyotaparts.com/

Runner4

I did a search on this site and can't find any O2 Sensors???

gwhayduke

Call 'em

ColImport

go to gadets site www.urd.com he is got them much cheaper dont buy at autozone. Try to clean the sensor first with electronic crc contact cleaner and reset the code and see if it comes back again if not then you would not need to buy one. If it comes back then you are sure you HAVE to buy it. By the way It is not going to hurt anything execpt your gas mileage by not replacing it right away. So that gives you some time to try and test it.

MTL_4runner

This test is very basic and does not effectively test slow response on an O2 sensor (the response is in milliseconds...much faster than your hands).
It is a good way to find if the circuit is broken

Here is the other part of the procedure for in vehicle testing (which is the method I prefer):

The engine must first be fully warm. If you have a defective thermostat, this test may not be possible due to a minimum temperature required for closed loop operation. Attach the positive lead of a high impedence DC voltmeter to the Oxygen sensor output wire. This wire should remain attached to the computer. You will have to back probe the connection or use a jumper wire to get access. The negative lead should be attached to a good clean ground on the engine block or accessory bracket. Cheap voltmeters will not give accurate results because they load down the circuit and absorb the voltage that they are attempting to measure. A acceptable value is 1,000,000 ohms/volt or more on the DC voltage. Most (if not all) digital voltmeters meet this need. Few (if any) non-powered analog (needle style) voltmeters do. Check the specs for your meter to find out. Set your meter to look for 1 volt DC. Many late model cars use a heated O2 sensor. These have either two or three wires instead of one. Heated sensors will have 12 volts on one lead, ground on the other, and the sensor signal on the third. If you have two or three wires, use a 15 or higher volt scale on the meter until you know which is the sensor output wire.

When you turn the key on, do not start the engine. You should see a change in voltage on the meter in most late model cars. If not, check your connections. Next, check your leads to make sure you won't wrap up any wires in the belts, etc. then start the engine. You should run the engine above 2000 rpm for two minutes to warm the O2 sensor and try to get into closed loop. Closed loop operation is indicated by the sensor showing several cross counts per second. It may help to rev the engine between idle and about 3000 rpm several times. The computer recognizes the sensor as hot and active once there are several cross counts.

You are looking for voltage to go above and below 0.45 volts. If you see less than 0.2 and more than 0.7 volts and the value changes rapidly, you are through, your sensor is good. If not, is it steady high (> 0.45) near 0.45 or steady low.


Here is the article where this stuff comes from (maybe not the originator since it has been reposted many times on the internet).

mt_goat

There is a test in the FSM if I remember correctly. I think it in involved using a multi-meter. I replaced my O2 sensor at about 100,000 miles and didn't notice any difference. I never had my CEL come on though.

midiwall

Correction: Gadget's site is http://www.urdusa.com

And yes, he's got the best pricing on original O2 sensors.

Runner4

Thanks those prices are Awesome compared to AutoZone. I think I will wait on the purchase, since the CEL turned off last night and hasn't returned. Maybe it was a fluke. I haven't seen any decrease in MPG, or performance yet. We'll see. Thanks for the info everyone.

Unhappy99

The CEL comes on when it sees two consecutive trips with the same failure. It goes off if it sees three consecutive trips with no error.

Since you have an OBDII ECU, the best way to see everything is by getting a real scanner which plugs into a PC or laptop. All the info the ECU sees is mirrored out the OBDII port and displayed on the PC.

http://obddiagnostics.com/

cheap and effective