O2 heater - code 1264

[Mook613]

Check engine light came on about 2 weeks ago... code 1264.

Tested the relay and wiring and found that the resistance on the heater coil for the O2 sensor was very low (too low for a working heating coil).
Also found that the fuse had blown for the heater coil.
So I ordered a new O2 sensor and installed it.

I Put the fuse back in, let the DME reset by unplugging battery for 10 minutes. Started car up and no CEL.

Next time I started the car the CEL came on and it won't go out.
It's not intermittent; it's a constant glow.

Any ideas?
My plan for tomorrow is to check all +/- and ohms, but not sure what else could be wrong.

[Mook613]

Tested:
1) have power confirmed at the heater wire for the sensor
2) have 3ohms of resistance at the heater coil
3) with engine warm I get 0.7 volts steady at sensor output. Got engine hot and still have steady. Assuming that the sensor is bad, BUT when I let air in by pulling dip stick it dropped right down to. 2v. Still indicates a bad sensor?

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[Mook613]

I disconnected battery to reset the code.
Was able to drive around for a bit without code coming back.
Then I hit the WOT switch, at which time the revs dropped and the CEL came on.

Anybody?? (could really use some help here)

[Mook613]

Nobody has any thoughts on this?

Just looking for help on how to even diagnose this.

[MrBurgundy]

The sensor could just be bad.

[Mook613]

Brand new o2 sensor.
Heater wires test at 3ohms and sensor wires are between 0.1 and 0.9 volts, so don't think it's sensor.

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[bmwman91]

What is the resistance of the pull-in coil on the heater relay? The DME will find a fault if the resistance on the pull-in coil is wrong.

[Mook613]

What is the resistance of the pull-in coil on the heater relay? The DME will find a fault if the resistance on the pull-in coil is wrong.

Do you mean the wire going to the relay or the wire going from the relay to the sensor heater?

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[bmwman91]

Terminals 85 and 86 of the O2 relay should read a couple hundred Ohms if I remember properly. See diagram here:

https://www.r3vlimited.com/board/showthread.php?t=248489

[Mook613]

Put in a new relay.
Tested wire to o2 heater and its giving me 12v. Also tested and gave good ground.
Pulled battery to reset ECU.
Code 1264 came back as soon as I hit the gas pedal.

Thinking that the ECU is the problem.

I hate throwing parts at a problem, but it's passing the tests and I can't think of anything else.


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[Mook613]

Swapped in a new ECU.

Fired her up... no codes.
Waited about a minute and then stepped on the gas a few times. As soon as I pressed hard enough that it would have hit the WOT switch (about 3/4 throttle) the engine dipped RPM for a second and then the CEL came on.
It is still giving me a 1264 code.

Anybody have any ideas???

I'm going to exchange the O2 sensor, but not sure what else to even try.
Have replaced the relays, the fuses, the ECU so far.

[Mook613]

I tested every wire that is part of the heater circuit. Also cross checked all of the grounds to make sure that they were isolated from each other.

Every wire is good; some showing .03ohms of resistance, but nothing of concern.

Test 02 heater again and it shows 3.5ohms (which is normal, I think). Over 5ohms is indication that the heater is dead.

I will see if I can get RockAuto to send me a new O2 sensor as it is the only thing left.

[paynemw]

I don't think the O2 sensor is the problem. Do you have the ability to get a wide band or see what your AFR could be.... not sure how you could do that other than potentially going to a testing facility.

[Mook613]

I don't think the O2 sensor is the problem. Do you have the ability to get a wide band or see what your AFR could be.... not sure how you could do that other than potentially going to a testing facility.

The O2 read isn't the problem here.
It is the heater part of the circuit.
I've confirmed that the heater is getting sufficient power and ground and have confirmed that the O2 heater/sensor wires to the ECU are good.
Only thing left that can be causing the problem is the O2 heater (which is part of the O2 sensor).

If you have a theory as to otherwise then please try to support it.

[Mook613]

Have tried a replacement O2 sensor and have the same problem.
Have tested all wires and all are good.
Have test relay, fuses, and all are good.

WTF???
HELP!