Paddo

Hi everyone,
I'm new here. I have a 2000 4Runner Limited (non-California spec exhaust). As the title suggests, I replaced both O2 sensors a few days ago, after my Check Engine light came on. I took it to AutoZone and that's what the guy said I should do (Codes P0135 and P0141). So I swapped them out, took it back to have the codes cleared, and the light came back on after the second start.

I've been searching for a few days now, trying to figure out what the problem could be since replacing the O2 sensors didn't help (seemed odd that both would fail at the same time, too). I'm beginning to worry it could be a wiring issue, which I don't have a lot of experience with. Any other ideas? I appreciate the help.

-Paddo

TheDurk

First question, since you were at AZ: Did you get anything other than Denso or Toyota sensors? Universal or plug and play?

Second, Are you absolutely sure you are not a Cali. rig? They were sold all over the country in 2000. You need to count your cats (2=Cali.) or check your emissions sticker. Post a pic of it if you are unsure.

Third, if you do indeed have the correct sensors, make sure your connectors are clean. Get any crud out, spray with contact cleaner, and pack with dielectric grease.

Fourth, if no joy, you will have to get a DMM (digital multi-meter) and check resistance of heater circuit at the plug and voltage at the truck-side connection. For this, you may need some help.

Paddo

Yeah, they gave me one Bosch and one other brand (Pilot or something?). They said they were OE sensors. I'm absolutely sure it's NOT California spec (one Cat.).

Will the brand of the sensors really make such a difference that it can't read them? If so, why would they sell me those ones for that vehicle?

TheDurk

You tell me.(Only Denso is OE, anything else is BS.) Test those sensors as described here (should apply to both):

(Note: the plug may be slightly different but the heater is measured across the two wires that are the same color. You should have four wires, two alike, plus two more of two different colors.)

Paddo

Okay, I'll be able to do that test once I get home. So that document is showing what should be the correct resistance?

The connectors looked pretty pristine. The diagrams showed which wires were the heater wires. It's pretty annoying that AutoZone would SAY they were selling OE sensors, and actually give me different brands. I'm guessing it's a little late to return those ones now.

It still seems weird to me that both sensors would fail at once, which is why I'm sort of suspecting a wiring issue further up, but like I said, car wiring is one of the things I have little experience with, though I do know enough about electricity and can use a multimeter to be able to fix stuff once I understand how it's wired.

Thanks again for the help!

Paddo

Okay, I'm gonna go test the resistance at the plug right now (it's snowing - Ugh). I don't know how to test the voltage at the other end, though. That's done at the ECM, right?

rworegon

Pull both those sensors out and ONLY use Denso or ones you buy from the Toyota dealer. It is well documented on this site and others that these rigs don't play well with other brand O2 sensors.

Also, before you install the correct sensor in the front and rear position. They may look the same, but function slightly differently.

TheDurk

No, they don't, on Federal rigs before 2001 like the OP. The proof is that Denso sells the SAME universal sensor (234-4206) for use in front and back. The only difference is wire length.

The front A/F sensors on Cali. rigs and all '01+ are indeed very different. But they have a different plug and will not connect if placed in the rear.

rworegon

I was thinking the difference between the A/F sensor and the O2 sensor. Some buy them without plugs and wire them up, so they don't have the plugs to reference.

TheDurk

Denso does not sell a universal A/F sensor, only O2. So if you use a universal on a 49-state, you NEED to use the same thing front and rear. And, as I said, OP's truck does not use the A/F anyway. No biggie, I just didn't want people to think there was a general difference between front O2 sensors and rear O2 sensors when there isn't any other than wire length (and the screw-in rears on '01 and '02.)

Potomacduck

Been there. Use original Denso equipment. I gave up on aftermarket parts years ago. 350,000 miles and still running strong.

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