The FSM Oxygen Sensor Test (1 Viewer)

[ZRotheohv]

I've been having oxygen sensor problems for a year now, and I recently replaced both of them on my '94. To make sure everything checked out, I wanted to do the test depicted in the FSM. But I have no idea what some of it is trying to say.

First you test the heaters' resistance (that makes sense). Then you connect your voltmeter to VF1 or VF2 and E1 (which, from what I understand, is ground). Then you connect TE1 and E1 to put it in "test" mode (so the CEL starts flashing its codes). Then apparently you're supposed to see your voltmeter fluctuate.

What are these fluctuations supposed to look like? Do they slowly go up and down? Or do they "flicker" around? On mine, I see a very steady 4.93 volts on both of them at 2,500 RPM. To continue with the logic tree, it fluctuated zero times (staying steady at 4.93), so with a code 21, I'm supposed to disconnect the jumper from TE1 to E1 and measure the voltages again. I get zero on #1 and about 1.5 on #2. But the only choices are 0 and 5! Where do I go if it's 1.5V?

For the zero volt sensor, it says to disconnect the PCV hose and measure again. What on earth could disconnecting the PCV hose have to do with anything? At zero volts again, it says I should replace it. But I got a brand new OEM one! I have a hard time thinking it could be bad.

If, after replacing the oxygen sensor, it still fluctuates zero times, it says to replace the ECM. I have a tough time accepting that. Are there other tests I can do? On the OBD1 port there are OX1 and OX2 connections, as well. Can I do some kind of test with these?

I attached the excerpt from the FSM...

 

[Oscar Witte]

The fluctuations are meant to read by an analog needle meter I believe. The fluctuations may be faster than the sample rate of your volt meter if it's digital.

 

[ZRotheohv]

Actually, I got an analog meter just for this test. Both the digital and analog gauges are solid at 4.93 for the fluctuation test!

 

[Warpigg]

I had a bad heater wire on my front o2 sensor something you may want to check into.

 

[Malleus]

It's a square wave function. On for some interval of time, off some interval of time.

 

[ZRotheohv]

So that would suggest both of my new sensors are junk... Any idea what should come out of the OX1 and OX2 connections in the OBDI connector?

 

[Malleus]

Here's Mr. T's wisdom (he knows way more than me):

 

[blkprj80]

If you engine isn't getting into closed loop mode, it may not fluctuate.

I think the ECU dithers the mixture, and it watches the o2 sensors upstream and downstream of the cat(s). The signal from the input side should be bigger than the signal on the output side, thus showing that your cat is removing the bad stuff.

I think you can do the same thing with an ELM-327 reader and a smart phone, and even graph it if you wish. The reader module is cheap, I own 2 of them.

 

[ZRotheohv]

Since I have a '94, the ELM-327 won't work with the OBD 1... But it does look like a cool little device!

I also don't have a downstream O2 sensor, but I do think you're right in that my engine never got to closed loop. But with 2 more GTK O2 sensors (OEM up until '94), it finally behaved the way I was expecting!

To answer my own question, this is what you should be seeing (at 2500 RPM):

 

[SnowroxKT]

On my 1994 I performed the test outlined above and didn't see any fluctuations at all, so 2 new NTK 24044 O2 sensors ordered from RockAuto. I was getting .08VDC at both Previously I had a code 26, now I have a code 28. Also have a code 12, but I think that is due to something else.

 

[masyam]

I just joined the forum because I have a very similar problem with my 94. I also replaced both O2 sensors with NTK24044 and it runs very rough and weak. After a few miles of driving the CEL come on and it is the error code 28. Somewhere in the forum I read that you need the Toyota O2 sensor or you are buying it twice. It seems that Toyota has discontinued O2 sensors for 93~94 models. I had someone installed an aftermarket(probably) O2 sensor that worked for two years or so, but I cannot find out who makes this sensor(picture attached). There is no writing on the sensor. Is there a known aftermarket O2 sensor that works with 94 Land Cruiser?

 

[SnowroxKT]

I just joined the forum because I have a very similar problem with my 94. I also replaced both O2 sensors with NTK24044 and it runs very rough and weak. After a few miles of driving the CEL come on and it is the error code 28. Somewhere in the forum I read that you need the Toyota O2 sensor or you are buying it twice. It seems that Toyota has discontinued O2 sensors for 93~94 models. I had someone installed an aftermarket(probably) O2 sensor that worked for two years or so, but I cannot find out who makes this sensor(picture attached). There is no writing on the sensor. Is there a known aftermarket O2 sensor that works with 94 Land Cruiser?

View attachment 2392462

Are you getting voltage to the plug? I wonder if the wiring on ours is corroded or burnt. I metered the heater circuit on mine and got 14V to it, so 1 of the 4 wires seems good. I bought some contact cleaner and sprayed the heck out of the harness-side plug.

I also metered my O2 sensor with a ohmmeter and got 5.9 Ohms, so that part seemed fine. Hoping its not the harness wiring, but if so I'll replace that I guess.

 

[masyam]

I'm reading about 12V at the connector. Signal wires also seem to be properly connected because if I remove the connector and start the engine, the ECL never goes OFF. With sensor connected I get ECL ON after driving a few miles. I would think that the NTK's are incompatible. NTK seems to have been working on the bank 123 with the other manufacturer's sensor on the bank 456. My problem started when I replaced the sensor on bank 456 with the NTK.

 

[SnowroxKT]

If i have issues after putting a new sensor in bank 2 I may try and rotate the 2 sensors. Have you tried that?

 

[masyam]

Yes, I have and the symptom did not change.

 

[SnowroxKT]

Might be the harness then.

 

[masyam]

I think the harness is fine because +12V is there and the ECU is sensing the signal. I think the problem is in the signal itself. I need to find a know compatible sensor to troubleshoot forward.

 

[SnowroxKT]

I bought my cruiser 9 months ago with the issue, so I'm not really sure what went into it before I got it. I bought it with a present 26 code.

 

[masyam]

Have you checked this thread below in this forum? He seemed to have a similar error code like you do.
"1994 Fj80 Code 26, running rough, and Oxygen sensor wiring"

1994 Fj80 Code 26, running rough, and Oxygen sensor wiring

Newbie here, My 94 land cruiser is idling a little rough upon starting. Problem gets much more severe when accelerating. Hesitation and cutting out when attempting to accelerate, when returning back to idle the shake is fairly severe. I have to this point: *Removed, cleaned and checked the EGR...

forum.ih8mud.com

 

[SnowroxKT]

Have you checked this thread below in this forum? He seemed to have a similar error code like you do.
"1994 Fj80 Code 26, running rough, and Oxygen sensor wiring"

1994 Fj80 Code 26, running rough, and Oxygen sensor wiring

Newbie here, My 94 land cruiser is idling a little rough upon starting. Problem gets much more severe when accelerating. Hesitation and cutting out when attempting to accelerate, when returning back to idle the shake is fairly severe. I have to this point: *Removed, cleaned and checked the EGR...

forum.ih8mud.com

Mine isn't running rough at all. Smells rich.