o2 sensor harness diagnosing 97 gsx 2g

[Cesar]

I am trying to diagnose my o2 sensor harness.

I have a new factory o2 sensor, and I am getting both heater/o2 sensor circuit malfunction.

What I am trying to figure out is how do I check for continuity for the o2 sensor.
there are four wires for the o2 sensor.

Wire - o2 sensor - harness
#1 - white - blue/yellow
#2 - black - green/black
#3 - blue - blue/orange
#4 - black - blue/black

I have checked the pin out for the 97 ecu and I have found that pin # 60 (I think it's a yellow wire) is the front O2 heater sensor and pin number 76 is the o2 sensor signal. (thick white wire)

How do I check for continuity between these wires? What about grounds?
I was told that one of the two grounds is not the same as chassis ground.
Is this true?
Why are the wire colors different when they get to the ECU? Where do they change color?
Thanks

 

[romeen]

I'm not sure about checking for continuity at the ECU but you can check for continuity of the sensor itself by checking resistance between pin number 1 and 3 on the connector. On mine they both respond to black wires with white going to pin #2 and blue going to pin #4. If you are looking straight at the connector oriented with the locking tab towards the top then #1 is upper left and #3 is right below it. If you have a multimeter set it at 200 ohms (I think 2000 will give you an accurate enough reading also).

If I misunderstood your question and your concern is with a problem at the ECU then I'm not sure how it corresponds.

 

[Cesar]

I have already checked the sensor for continuity. The sensor is new, and I would like to check the rest of the circuit for a break/short or something.

I have been reading up on this topic, and I found that the mpi relay activates the sensor. I guess I'll check that as well when I check the sensor circuit tomorrow.

 

[luv2rallye]

Your wiring does not appear to be standard. Also the colors should not change on way to ECU. Yes the sensor signal ground must not be connected to chassis ground - it goes to ECU pin 92. http://www.dsmtuners.com/forums/showthread.php?t=244376

 

[Cesar]

Your wiring does not appear to be standard. Also the colors should not change on way to ECU. Yes the sensor signal ground must not be connected to chassis ground - it goes to ECU pin 92. http://www.dsmtuners.com/forums/showthread.php?t=244376

I didn't know about pin 92. The pinout that I checked did not point that out.
I also wanted to know, since I can only check the power for the heater circuit when the mfi relay is activated (open or closed, I don't know) couldn't that be here the wires change color?

Thanks guys, I'll keep you posted.

 

[luv2rallye]

Pin 92 is the signal ground for many sensors and must not be connected to chassis ground or your engine will not run right. My 99 factory Mitsu manual shows O2 sensor red (heater) wire stays same color all the way to MFI relay (where it gets +12V when activated). On the front O2 sensor, I do see however, 2 other wires change color (but not to what you state). The other black heater wire becomes yellow (goes to pin 60) and the black/white signal ground becomes black (goes to pin 92). FYI note that the front O2 sensor heater black wire (which becomes yellow) is grounded inside the ECU pin 60.

 

[Cesar]

I have checked the resistance on my o2 sensor to find that it reads just above 15 ohms. Is this normal? I also got a reading of 590 ohms from the heater ground to the negative battery terminal. That doesn't seem normal.

On a different note. I was cleaning up some of the wiring for the radio and something must have shorted out. What would cause my radio, antenna, door ajar buzzer, and my diagnostic port to die and have no power? I can't check my codes now, specially since the CEL doesn't come on now. It lights when I turn the key to the ON position, but then it goes away, even though I know that I have like 6 codes. (all those useless solenoids).
I didn't even disconnect the battery for the codes to reset, they just went away. All because I moved the radio, all that stuff died.

 

[luv2rallye]

I have checked the resistance on my o2 sensor to find that it reads just above 15 ohms. Is this normal?

Yes the heater should read between 11-18 ohms at 68F.

I also got a reading of 590 ohms from the heater ground to the negative battery terminal. That doesn't seem normal.

That measurement is meaningless since you are measuring across internal solid state circuitry of the ECU (which is primarily a transistor that turns on to connect to ground but now is turned off - so you are just measuring across other internal "stuff" that's in there). The measurement has no meaning and could be anything.

 

[Cesar]

Yes the heater should read between 11-18 ohms at 68F.
That measurement is meaningless since you are measuring across internal solid state circuitry of the ECU (which is primarily a transistor that turns on to connect to ground but now is turned off - so you are just measuring across other internal "stuff" that's in there). The measurement has no meaning and could be anything.

It seems I have no voltage for the heater on the o2 sensor harness when the car is running.
I will check again, but the car should have continuity between the heater ground and the negative terminal on the battery with the car running?

If I have no voltage, could it be a faulty relay?

Thanks

 

[luv2rallye]

It seems I have no voltage for the heater on the o2 sensor harness when the car is running.

You mean when you measure directly across the heater? If so that's bad.

I will check again, but the car should have continuity between the heater ground and the negative terminal on the battery with the car running?

Yes but probably only with the car running. Mitsu does not provide diagrams of the ECU internals but speaking as a electronic design engineer, the ECU would turn on a transistor that ties the heater ground to battery negative only when the engine is running. I ADVISE NOT to try measuring this with an ohmmeter however. This is because should there be no continuity, you will have 12V on that O2 sensor wire (thru the O2 from it's other side +12V wire) which will damage your meter. If you really want to test this path, unplug the O2 and connect a small 12V light bulb from the heater ground pin in the harness side connector to battery positive. It should then light when engine runs.

If I have no voltage, could it be a faulty relay? Thanks

There is no relay for this (other than the MFI relay that provides +12V to this and all the other sensors, injectors, and ECU - but if that was bad your engine would not run). If you have +12V (measured to ground) on the other heater wire (MFI relay side), then the only way to not get 12V across the heater would be either a bad connection from heater ground to ECU pin 60 or a bad ECU.

 

[Cesar]

You mean when you measure directly across the heater? If so that's bad.


Yes but probably only with the car running. Mitsu does not provide diagrams of the ECU internals but speaking as a electronic design engineer, the ECU would turn on a transistor that ties the heater ground to battery negative only when the engine is running. I ADVISE NOT to try measuring this with an ohmmeter however. This is because should there be no continuity, you will have 12V on that O2 sensor wire (thru the O2 from it's other side +12V wire) which will damage your meter. If you really want to test this path, unplug the O2 and connect a small 12V light bulb from the heater ground pin in the harness side connector to battery positive. It should then light when engine runs.


There is no relay for this (other than the MFI relay that provides +12V to this and all the other sensors, injectors, and ECU - but if that was bad your engine would not run). If you have +12V (measured to ground) on the other heater wire (MFI relay side), then the only way to not get 12V across the heater would be either a bad connection from heater ground to ECU pin 60 or a bad ECU.

I just double checked the harness side of the o2 heater circuit. No voltage with the coolant temps above 80. I'm gonna check the ground to pin 60. I hope that once I fix the heater problem, it'll stop throwing the o2 circuit code.

 

[Cesar]

I am in the process of tracing the 4 wires from the o2 sensor harness to the ecu. I have traced them back to the blue connector behind the radio. That connector also contains 2 wires from the TPS. One is brown with a red line, and the other is a yellow wire with a red line though it.

Does anyone know where these wires go to? It's seems the harness goes behind the gauge cluster, then to something by the clutch pedal. This is getting frustrating....