Resistance In Oxygen Sensor

[stroked4.6]

I’ve had this check engine light on since I bought the car and am trying to resolve it now. I had two codes: egr and rear o2 sensor. I replaced the egr temp senor since that resistance was crazy high and now im dealing with this rear o2 sensor. I bought a new one and the light is still on. Code 28 keeps showing. I printed all the flow charts and diagrams on alldata but am not sure about one thing.

I bought a Denso specific oxygen senor but it ohms out too high. I turned the car off and waited about an hour and it was ohming out at 60.3 ohms. Today with the car very cold and 30 degrees (F) outside it ohmed out at 16 ohms.

The spec should be 11.7-14.3 ohms at 69 degrees Fahrenheit (20 degrees celsius).

Now would this keep the light on so should I buy an original Toyota oxygen sensor or do some more testing on the wires. I did some testing and was getting the correct voltage everywhere.

[Rob Mc]

COuld possibly be bad right out of the box, I've had that happen to me with various auto parts. Try swapping it out with another from the parts store and see if it reads differently.

[djspawn00]

I agree with the bad part theory, I spent a nice chunk of change on an A/F ratio sensor from denso just to have it be defective, sometimes bad parts happen to good people.

[stroked4.6]

I bought an OE Toyota O2 sensor and the light is still on. I was getting code 28 which is O2 sensor heating element. I ohmed the Denso sensor out and there was too much resistance so I figured a Toyota sensor would solve the problem. Unfortunately I have to do some more electrical testing tomorrow. I tested some of the wiring and it was good so now I have to trace a couple of the wires I couldn’t get to. I wasn’t able to get a couple pins for the ECU since the holes were too small even for paper clips so i guess Ill try some needles. I’ve got all the instructions from alldata on how to diagnose this so I guess if its not the wiring the last thing to do would buy a new ecu. I have credit to a junk yard and they have a 95 gs300 w/cali emissions so I guess that’ll be the next thing to do. Im hoping to finally be done with this car so I could start my other project. Im only a few bolts away from removing the Stangs engine!!

As long as the numbers match I could drop in the new ECU (95 GS300 w/ Cali emissions) in my car with no problems right? I’ve got a 93 GS300 w/ Cali emissions. I previously installed this ECU quickly and the car started but would there be any other minor problems. The keyless entry doesn’t work anyway so im not worried about that.

[stroked4.6]

Well I got that 95 GS300 ECU and the car runs but that engine light is still on!!!!!!! Ive got the glove box out and many wires disconnected trying to find this problem. Im tracing wires back as far as they can go and the resistance in the wires seems fine. Im going to test for continuity next on all the wires. I spoke with my boss and he said this engine light only came on about a year ago or a little more. Im going to see what code is coming up now with this new computer.

I was thinking maybe the light is grounded but no code would come up if that was the case. There has to be short or ground somewhere on this circuit its just a matter of tracing the wires back since they go throughout the dash. If anyone has any ideas please post and let me know.

Thanks in advance

John

[stroked4.6]

I have most of the dash apart at least all the pieces that come off (not entire dash) so I could see the starting and ending points off all the wires. My main problem is between the instrument cluster (left) and computer (right) its behind major parts I cant remove (metal brace and a/c components). Any ideas or oxygen sensor wiring diagrams i could use.

Anyone know the color of the wire which goes to the back of the instrument cluster from the computer which controls the check engine light?

[Texas_GS300]

I have most of the dash apart at least all the pieces that come off (not entire dash) so I could see the starting and ending points off all the wires. My main problem is between the instrument cluster (left) and computer (right) its behind major parts I cant remove (metal brace and a/c components). Any ideas or oxygen sensor wiring diagrams i could use.

Anyone know the color of the wire which goes to the back of the instrument cluster from the computer which controls the check engine light?

Well as you said the short circuit would not be from the ECU to the check engine light in your dash it must be in the oxygen sensor circuit. I guess you would need to buy the electrical circuit diagram manual of the car to trace the wire from the sensor to the ECU. I am myself in the same problem. My sensor is readying 137ohms and I've ordered a replacement toyota denso sensor but I doubt that it will have the right 11 - 16 ohms resistance for the heater element. I found a forum online actually it was on this owner's forum where someone has attached a pdf file of the sensor circuit. I downloaded it and used it to trace my sensor too. Those couple fo pages were very helpful. I am going to see if I can locate it again. If I did I'll post it here.