Oxygen Sensor Troubleshooting

I got the OBD cable and software loaded up on the laptop and had a chance to do a quick test over lunch. 

These are the errors currently reported. 

I need to play around with it more after work to see what live data I can view and get more info. I'm curious what the short to V batt means with the low idle code. 

Short to Vbatt would mean 12V is being detected where it should not be.

Whereas the short to ground is 0V where it should not be.

So the heater lines are being shorted to ground somewhere, and the IAC is getting full 12V somewhere.

Upstream. Downstream.  New O2 sensors. Check engine light.     

Guy at auto parts store tells me of a trick outsmarting them by using an anti fouler.

I would never illegally change out a part.   

After watching the data the front O2 is working, the rear is not (0.41V constant). The front starts around 0.8-9 when it runs fine on startup and drops to 0.08-0.1 when it starts to run bad. 

Also from the data when it starts to run bad the ignition angle set point goes from around 18 to max at 72. While it is running like that the reported ignition advance is around 15. Not sure if that is a syptom or cause. 

In reply to EvanB (Forum Supporter) :

The front sensor will eventually heat up on it's own to work, the rear one has a tough time doing that without some driving around.

With the heater fault it's seeing, neither will be getting any to try- the computer is smart enough to not run a high amperage 12V circuit that is know to be grounded somewhere.

With a heater circuit fault you need to put down the scantool and pick up a voltmeter and poke around checking wiring.  9 times out of 10 it's a bad oxygen sensor or blown fuse, the rest of the time it's usually a bad ground circuit on vehicles where the ground doesn't go through the PCM.

I wish I'd checked this thread before coming home from work.  There are so many fingers in the pie that is first generation Mini (Chrysler engine made in Brazil for a British company bought by Germans halfway through development... I think) that I couldn't say for certain whose design philosophy was involved in any particular thing.  This is part of the Mini charm.

With as many times as the car has been apart recently for repair, chafed wiring due to manhandling of the harness or not correctly routing the loom becomes a distinct possibility.

Pete. (l33t FS) said:

With a heater circuit fault you need to put down the scantool and pick up a voltmeter and poke around checking wiring.  9 times out of 10 it's a bad oxygen sensor or blown fuse, the rest of the time it's usually a bad ground circuit on vehicles where the ground doesn't go through the PCM.

I wish I'd checked this thread before coming home from work.  There are so many fingers in the pie that is first generation Mini (Chrysler engine made in Brazil for a British company bought by Germans halfway through development... I think) that I couldn't say for certain whose design philosophy was involved in any particular thing.  This is part of the Mini charm.

 

With as many times as the car has been apart recently for repair, chafed wiring due to manhandling of the harness or not correctly routing the loom becomes a distinct possibility.

Would the heater circuit fault explain why it starts and idles fine for a few seconds (every time) but then the idle drops and it won't respond to throttle? 

No fuses blown. 

No change with the front o2 unplugged so they both read 0.41V while running. 

I inspected the wiring for the pre-cat o2 sensor. There were some splices covered with heat shrink (maybe it was extended for the aftermarket header?) and two of them were rubbed through. I wrapped them all with electrical tape and cleared the codes. Now the only code that came back is the rear o2 no signal. The front o2 is showing 0.15-0.2v while it is running bad. I was able to get it warmed up and after revving it a bit with light throttle it settled into a decent idle at 800rpm or so. I let it run like that for about 10 minutes and it revved with part throttle but too much throttle would send it back to idle. I shut it down to cool off for a bit and again it won't take any throttle (doesn't die, just doesn't rev). 

Sounds like multiple issues to resolve.  Glad it idles okay now.

In reply to eastsideTim :

Well it did, I haven't been able to get it to idle well again after it cooled off for a bit. 

Had a friend watch the throttle plate while it was running and it does open based on pedal position. It doesn't affect the running at all but I think that means the throttle body should be ok. 

For anyone still following along. I found the area in the software to temporarily change the fuel trims. Moving the fuel trim up to +1.0 gets it to idle well. Revert back to ecu control and it goes back into the same low idle. Looking at live data of short and long term fuel trims and everything is zero. 

So the ECU has decided it doesn't have enough data to make adjustments?

Not sure if it is not enough data or just isn't making the adjustments for some reason. All other sensors seem to be reading and it doesn't show any faults for any of the sensors in the software. 

The only thing I have noticed that could be a potential air leak is a cracked weld in one of the joints on the aftermarket header. I would still think the computer would try to compensate for that, especially since I can make a large difference by only bumping the trim up to +1. 

Well I at least found out why the rear o2 sensor has no signal (ignoring the fact that the cat was installed backwards so it is before the cat). I found the connector for it and it didn't look to be plugged in all the way. I cleaned it up and tried to plug it in but it won't go all the way. Turns out the keys on the sensor plug are different than the vehicle side connector so it isn't even the correct sensor.