Oxygen sensor trouble

[Kieran]

/help

I've had an oopsie with my 02 sensor. Today I pulled the original O2 sensor out and yes, it looks to have been poisoned. So I wired in a replacement "Universal" 4 pin sensor.

Here's how I spliced the wiring to the original harness:

2 Black cables: 02 sensor heater + & -
White cable: 02 signal wire to ECU
Blue cable: 02 sensor earth wire

Problem is I get 0v from the O2 sensor according to Evoscan. There is no fault code (I believe this is because the ECU measures the heater circuit to assess the state of the 02 sensor).

The heater certainly works. within a few seconds of switching on from cold, the sensor is too hot to touch - the rest of the exhaust is still cold.

If I swap the blue and the white cable around, I get 0.039v register in Evoscan, but nothing else. It all worked fine before. Whilst driving, there is no difference in 'feel' - but then the original sensor was shagged and the car was over-fuelling anyway.

I have rechecked the wiring (the splicing was okay) and re-soldered the joints just incase, to no avail. I am thinking it may just be that this sensor is Dead on arrival?

My questions are as follows:

Have I missed anything?

Have I identified the original wires correctly?

[Nick Mann]

You have identified correctly, IMO. I put a multimeter accross the blue and white wires last year, and was measuring voltage there. The voltages were as recorded by Evoscan, 0-1V. If the new one ain't doing that, then its either foobarred or incorrect for application. The only thing I would say is that it took a few minutes for the sensor to start its merry swing from rich to lean.

[Kieran]

OOOOOOOOoooooohhh..... I was trying immediately after starting up! Maybe I have been too impatient!:thinking: /pan

I'll try again tomorrow!:scholar:

[Kenneth]

FYI, the ECU does NOT monitor the heater circuit... You can disconnect it and it wont complain at all :)

This way you can wire in a wide band and use the simulated narrow band output and the ECU does not complain... saves having to use 2 sensors. Kinda makes it pointless to replace the OEM sensor with anything other than wideband really

[VR4 MAD]

FYI, the ECU does NOT monitor the heater circuit... You can disconnect it and it wont complain at all :)

Hey Kenneth, could you clarify what you mean when you say " disconnect it". Do you mean the heater circuit part of the sensor, or the complete O2 sensor.

I would expect the ECU to complain if it doesn't get any signal from the sensor and cause an error code to be generated. That not so?

And the ECU must have some sort of default mode or fuel maps to go into if the sensor fails during normal use rather than just stopping the car dead, surely. Isn't this what Kierans car must have been doing if his previous sensor was stuffed and causing the car to over-fuel?

Cheers.

/toycar

[Kieran]

Part of the problem is with both sensors (the new one and the busted OEM one) that the ECU was still 'seeing' an operational O2 sensor. In the case of the original, both heater and signal were working, but the signal being sent to the ECU was erroneous because the sensor had been contaminated.

I am surprised that disconnecting the heater circuit doesn't throw a code - I thought it would, particularly as the ECU has been quite happy with zero volts coming through on the 'signal' line. However, as Nick points out, I didn't give the car change to warm up - Maybe the new sensor is slower to come to operation temperature than the old, I dunno. I will faff about tomorrow with it some more.

[Kenneth]

I am not sure if it throws a code without the sensor, it may do but I don't think it throws a CEL...

The heater circuit is really only to warm the sensor up... The sensor would warm up in ordinary use anyway, it would just take longer before the ECU could/would use it. (It needs to be at the correct temperature to be accurate)

The ECU doesn't NEED the O2 sensor, it just happens to be a good way to ensure the emissions are correct (if the sensor isn't faulty). Without the sensor it just uses the AFR mapping and air flow. The O2 sensor is more accurate way of ensuring 14.7 AFR, and it allows the ECU adjust the fuel trims.

when I said disconnect, I was referring to disconnecting the heater circuit. However I ran a LC-1 narrow band simulation by disconnecting the O2 sensor completely and just tapping the O2 sensor input to the ECU (1 wire)

[VR4 MAD]

..................but I don't think it throws a CEL...


CEL..............!!!!!??????? :speechles

Sorry, must be really stupid but whats CEL stand for............./Grrr /pan

/toycar

[Kenneth]

CEL..............!!!!!??????? :speechles

Sorry, must be really stupid but whats CEL stand for............./Grrr /pan

/toycar

CEL = Check Engine Light :)

[VR4 MAD]

CEL = Check Engine Light :)

I knew that..............honest. /pan

Runs and hides in corner with pointy hat with a big D on it /dunce ............./duh /duh

[gee118]

I'm looking to make sure my sensor is in proper working order.
I don't have evoscan or anything like that but is there a write up as to how to check using a multimeter?
I'm unsure as to which pins exactly to check across and can't find it using a search. A pic would be great of course....

[I-S]

It will typically confuse a multimeter because it is switching. An oscilloscope or substitute (ie evoscan) is best.

[Nick Mann]

A cheap multimeter will not be confused, but it will not be able to settle on a voltage. That being said, if it doesn't settle its a good assumption that your sensor is working well.

If you look just in front of the ECUs, near the floor on the passenger side, you should find a four wire connector. It is coming through the floor from the O2 sensor. The wire colours are identified by Kieran in the first post. Put your multimeter accross the blue and white wires and then watch it for a few minutes. It may not bounce around whilst the sensor is cold.

[Turbo_Steve]

Agreed: if you can use a cheap, mechanical meter (with a proper swing meter instead of a digital readout) you should see it moving up and down once everything is warmed up.

[miller]

I'm looking to make sure my sensor is in proper working order.
I don't have evoscan or anything like that but is there a write up as to how to check using a multimeter?
I'm unsure as to which pins exactly to check across and can't find it using a search. A pic would be great of course....

Failing all of the above ill bring my HHH logging equip home at christmas and it will show the o2 sensor cycling or not.
You near Dublin at all? I will be in Navan but in and out of Dub from time to time over christmas

Let me know.


Mike

[gee118]

Thanks Miller, in Clontarf.

[miller]

pm me nearer the 20th December if your still having trouble and we can organise a meet up somewhere.


Mike