Oxygen Sensor Wiring

[Mike B.]

I have had a couple discussions with Jason89i about this and potential fixes, so I though I would put it out there to see if it's an issue consistant with the M/S50 swaps.

I noticed my swap is running a bit rough when warmed up so I checked the wires coming out of the O2 relay, when the ignition is switched, I get approx 12v on the brown/green wire (switched ground from DME that triggers heater) and 0v on the green/blue (or just green) wire (heating element).

So apparently, I'm not getting power to the heating element.

According to the ETM the O2 sensor on the E36 M50 gets it's power from
the harness and should'nt have anthing to do with the C101 wiring. The relay has power and it's not the relay itself as I have tried a new one. I find it really strange that there is no voltage to the heating element.

Could a few of you check the voltages coming out of your O2 relays to see if they are consistant with what I am finding?

If you are getting proper voltage at the green/blue (or green) wire, how do you have your O2 sensor wired up. If it's consistant with what I am seeing, I wonder how many swaps aren't properly heating up their O2 sensors.

[Jason89i]

go grab the voltometers! this will be an interesting thread. this should be made into a POLL type post.....does your green wire off the o2 sensor get power? vote YES or NO.

cheers, jason

[Mike B.]

We now have a poll.

[Mike B.]

Here is the wiring diagram from the ETM:



When that switch in the relay closes (30-87), we should be getting 12v to the O2 sensor heater. However, this does not seem to be the case.

[Rev Engineer]

From what I can tell, the DME switches ground to the relay. If you're measuring +12V on the brown/green, then the relay is off and you should get 0V on the green wire. When the DME switches ground to the brown/green wire, then the relay is on and you should get +12V on the green wire.

[Mike B.]

From what I can tell, the DME switches ground to the relay. If you're measuring +12V on the brown/green, then the relay is off and you should get 0V on the green wire. When the DME switches ground to the brown/green wire, then the relay is on and you should get +12V on the green wire.

That may be correct, however, I am getting 0v on the green wire during start and run. So that would lead me to believe that the DME is not making the switch for some reason.

If you could check and see what yours reads during start/run and report back, that would be great.

[Rev Engineer]

I confirmed your findings. No voltage on the green wire. It's about 35F out so I expected to see it come on. Since there is voltage on the brown/green wire, it's the DME that's not turning the relay on. Could it be non-stock software? I'm running the Conforti chip. Maybe it needs to get colder before the DME decides to turn it on?? Certainly a little weird. I agree that this should have nothing to do with the C101 connection. It's all self-contained in the obd-i harness. Maybe a drive transistor blown in the DME? I would think something like that would set the CEL. No CEL codes here.

You mentioned that your problem was after the car was warmed up. How did this lead you to check the o2 heater relay?

Maybe the DME tries to run closed-loop off the o2 sensor and if it succeedes than it doesn't try to run the heater. I'm very sure that running open-loop for some period of time will set the CEL. Any codes on your end?

[Mike B.]

Since the car started to run rough after warmup, I thought I would check O2 sensor wiring from the DME to the sensor and noticed that the heater was not working properly. It's my understanding that if the O2 sensor heater does not come on, the DME uses some default settings for exhaust temp to run in closed loop.

I don't think it matters that you have non-stock software. I have a feeling that most, if not all, of the x50/52 swaps have improper O2 sensor heater operation.

I have not check the codes yet, as I don't have access to a code reader. No check engine lights have come after a month of running.

[Rev Engineer]

Very interesting.... Any ideas as to why swap/conversion cars would have a problem with this? I don't think that the DME can detect if the heater is working - only if it's able to run closed-loop. My engine is running fine, so I'm not sure if this is really a problem. Isn't the heater only suppose to be on for some short period after a cold-start?

As far as I know, the obd-i codes can be read by the gas pedal trick. Does anyone know if the DME stores codes beyond what can be read by the gas-pedal trick?

[tonytony]

about the non-stock software: I have the stock chip in mine and my ground switch does not work for the fuel pump and o2. So it can't be the chip

[Jason89i]

......... I have a feeling that most, if not all, of the x50/52 swaps have improper O2 sensor heater operation. ......
.

i have yet to see an e30m50 that was correctly wired or had ALL of the engine management systems working properly. here is a copy of the email i sent you a couple of months ago. this might help someone find the source.

Mike –

It is a VERY puzzling problem. I too had the same issue. Glad to hear that you have taken the time to check out your car after it was completed. Im guessing that most of the conversions out there are running without the o2 preheat.

Its near impossible to explain over a keyboard. It has to do with the e30’s integrated fp/02 relay and the e36 using separate relays. Ultimately, the system is being back fed by the e30 chassis…..but here’s the spooky part……it doesn’t show up on any wiring diagrams. I have MANY hours logged trying to find the source, but have ended up empty handed. However, I have discovered a fix. Its a little different on each car, so I would need a little time under the hood. ........ Cheers, jason

[Mike B.]

Since the FP relay is working properly, could one run the sensor heater off of this relay? Essentially make the FP relay a dual purpose relay.

One problem would be that the heater would run continously as there would be no contact with the DME to turn on/off the heater.

[tjhartge]

That may be correct, however, I am getting 0v on the green wire during start and run. So that would lead me to believe that the DME is not making the switch for some reason.

If you could check and see what yours reads during start/run and report back, that would be great.

If the DME doesn't make the switch to the heater relay, then this would then be the root of the problem wouldn't it?
There must be an input/sensor somewhere to inform the DME to switch it on for a certain time, then switch if off later when the O2 has heated up

tracing back to the engine temp sensor/coolant sensor, since we are running m20 sensors, would this then be the link for the DME to switch the heater relay on and off based on the temp sender from this particular sensor

[tonytony]

tracing back to the engine temp sensor/coolant sensor, since we are running m20 sensors, would this then be the link for the DME to switch the heater relay on and off based on the temp sender from this particular sensor

OT this is far reaching but having my o2 relay jumped, could that affect the temp guage?

I also searched around for answers and i came up with jason's old thread.

http://www.r3vlimited.com/board/showthread.php?t=55208&highlight=o2

fuel and o2 relays have combined wiring for e36's. check the o2 relay. green wire should be sending 12v directly to the o2 heater. likewise, the red/white wires should be 12v. i would bet that you are not getting the 12v .......and it is causing the red/white wires to backfeed too. disconnect the green/violet wires at the c101 and pull power (via fusable link) from fuse 11 (fuel pump fuse) to green/violet (e36 harness wire) at c101. i capped off the green/violet wire on the e30 side.

how would one pull power from the fuse 11 for the green/violet wires? also, if i disconnect the green/voilet wires at the c101 where would i draw power from for fuel pump. I'm a bit confused:( I think you mean x20 on the e36 harness side right?

[permit]

I'm having this issue as well, and have had it since I did the M52 swap (worked fine with M50). The CEL has been on for over a year now, and the code it throws out is for the O2 sensor. I had talked briefly with Jason89 a while back about what wires to check, but I never got around to checking them. I presume my heater wire isn't getting power--as is the problem with everyone else, so the O2 sensor is working off a default program. My motor runs fine regardless, but I'm sure it's messing with it enough for the engine to not be running flawlessly (gas mileage, etc.).

If anyone figures out why that particular wire wouldn't be getting power, that would be awesome.

BTW; the pedal trick is: turn key to second position (don't start the car), and stomp on the gas pedal 5x. The CEL light will then start blinking a (4?) digit code (1121, 1211, something like that is O2 sensor), and that's the problem.