1995 Toyota Pickup



April, 4, 2007 AT 2:31 PM

I just purchased a '95 Toyota Truck 4x4, 22RE, with 105k miles. When I bought it, it had a check engine light on. The lady said that it has been on since she bought it (she bought it in 2000, with 70k miles.)

So I replaced it. The first time I put a Bosch universal on it, cleared the ECU (both by disconnecting the battery, and removing the fuse), started it up, and immediately the check engine light is back on, reading the same code 21.

Then I returned that one, and got one from a Toyota dealer, put it on, reset the computer, started it up, and the light still is on!

To be sure that the computer is being reset, I removed the throttle position sensor, started it up, read the codes (throttle position sensor and oxygen sensor) turned it off, reset the computer, checked the codes. Sure enough, the TPS code was gone, oxygen sensor code still remained.

Then I checked the wiring. Followed the wires from the oxygen sensor all the way to where they enter the firewall to go to the ECU, tapped into it. Again, no problem, there is continuity between there and the sensor.

So what other options do I have left? Any ideas would help! Thanks so much!


9 Answers



April, 4, 2007 AT 3:37 PM

Since the posting, I have removed the computer, cleaned the plug-ins, and tested for continuity between the computer and the oxygen sensor. So there are definitely no shorts in the wiring. Help!



April, 4, 2007 AT 5:21 PM

Which one did you changed the heated one or the the other. The heated one has 4 wires to it.



April, 5, 2007 AT 6:33 AM

I changed the only one I knew of. The one on the exhaust (before catalytic converter). There is another? If so, where?



April, 5, 2007 AT 7:28 AM

In my book it says two the other should be after the Cat. The one you changed did it have 4 wires on it and is it OEM.

***** Then I checked the wiring. Followed the wires from the oxygen sensor all the way to where they enter the firewall to go to the ECU, tapped into it. Again, no problem, there is continuity between there and the sensor****

New O2 sensor-no wire problem-than it has to be the ECM> something tells me to recheck the wire-

Explain to me how did you check the wire? You said good continuity-is this wire end to end-how about checking the wire whether its touching together going to the O2 sensor.



April, 5, 2007 AT 7:54 AM

I had called a Toyota dealer shop about the possibility of two oxygen sensors, and they said this vehicle only has one (to confirm, I checked my buddy's 95 Toyota Pick-up. No oxygen sensor after the catalytic converter.)

I checked the continuity by tapping into the wire before the plug-in on the oxygen sensor (not on the sensor's side), and at the plug-in into the computer with a self-powered test light. I suppose I should check before and after the oxygen sensor plug-in just to be sure that it is connecting right.

Is it possible that my converter is clogged? Or even possibly that a small exhaust leak (after converter) could be causing it? Thanks!



April, 5, 2007 AT 8:04 AM

You need to scan the O2 sensor whether its switching or flipflopping

Small leak after the Cat has no bearing

Exhaust restriction: pressure test it anything over 3lbs calls for concerns on Cat or Muffler.

Check the EGR thoroughly-look for carboned-up area that can be creating vacuum leak and the computer is reading it thru the oxygen sensor



April, 5, 2007 AT 8:16 AM

Here's more

The O2 sensor reads unburned oxygen in the exhaust, and generates a voltage signal that is proportional to the amount of oxygen in the exhaust. The signal can vary from a low of about 0.1 volts up to a high of about 0.9 volts. A low voltage signal indicates a lean fuel mixture. A high voltage signal indicates a rich fuel mixture. The engine computer uses the O2 sensor's input to balance the fuel mixture during closed loop operation. A bad sensor may prevent the system from going into closed loop, and usually causes the fuel mixture to run rich causing an increase in fuel consumption and emissions.

A low voltage (lean) reading may indicate a bad O2 sensor, a vacuum leak, or a condition that allows unburned oxygen to enter the exhaust. Check intake vacuum at idle, and inspect vacuum hose connections. If okay, check for a misfiring cylinder, a burned exhaust valve that is leaking compression, or a leaky exhaust manifold gasket.

O2 sensor quick checks include watching the sensor's output voltage as the fuel mixture changes. Momentarily disconnecting a vacuum hose will cause a lean response from the O2 sensor. No change in the reading or a very sluggish response would indicate a bad O2 sensor.

NOTE: If you get an oxygen sensor code plus a random misfire code and a MAP sensor code, the engine probably has a serious vacuum leak.



April, 5, 2007 AT 8:31 AM

One note. Another mechanic had noted that my engine was particularly " carboned up". That being said, say my EGR valve is clogged or vacuums are clogged up (I have checked thoroughly for vacuum leaks). What can I do to clean them?

Another note. My check engine light comes on after maybe a second or two, even after resetting the computer. Does that point us in any one direction more than another? How do I check voltage readings on the oxygen sensor?

Thanks so much for your help!



April, 5, 2007 AT 9:29 AM

Scrap it out and use some sort of decarbonizing cleaner

You need a scan tool-to see what the oxygen sensor is doing.

You can read the O2 sensor s output with a scan tool or digital voltmeter,

A good O2 sensor should produce an oscillating waveform at idle that makes voltage transitions from near
minimum (0.1 v) to near maximum (0.9v). Making the fuel mixture artificially rich by feeding propane into the
intake manifold should cause the sensor to respond almost immediately (within 100 milliseconds) and go to
maximum (0.9v) output. Creating a lean mixture by opening a vacuum line should cause the sensor s output to
drop to its minimum (0.1v) value. If the sensor doesn t flip-flop back and forth quickly enough, it may indicate a
need for replacement.

Good Luck

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