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Can't clear CEL

Discussion in 'E36 (1992-1999)' started by steven s, Oct 24, 2012.

    • Member

    steven s

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    Here's the deal.

    I had a local guy replace my subframe bushings.
    He went over the car and said he tightened up the 02 sensors and bolts on my headers. IDK why he was messing with it. Guess he was doing me a favor. [IMG]

    I leave the shop and my CEL is ON. I scan the codes with my Peake while at the shop. Two bad precat sensors. He checks it on his scanner. Same thing. He measures the voltages. Both within spec. He tries to clear the codes. Nothing.

    I hook up Torque to see if I can measure voltages.
    I can see my OBD-II to BT adapter is connecting to my phone but not to the ECU. I try another adapter and my Nexus7. Same thing.

    So what is in common is that Torque, shop's scan tool and my Peak are all having problems with the ECU.

    My car runs fine. Haven't noticed anything with gas mileage.

    Do I need to bring my car to the dealer and have them connect it to their Modic to clear the codes?

    So far googling says to replace both sensors.
    But the values are normal.
    And even if the sensor was bad, I should be able to clear the code even for a short period. The CEL goes off for a second but the faults never go away. :(
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    • Technical Service Advisor

    charlson89

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    What exactly was the fault code description was short to ground or short to positive, or o2 posioned? Also what voltages did he measure? Doesn't e36 only have one precat o2 and one post cat o2 are you saying both are giving you faults?
    • Member

    steven s

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    The Peake just tells me bad pre-cat O2 sensors.
    My car has (2) precat and (2) post cat.
    I don't recall what the voltages where, but they where both similar and within spec.

    It's odd that they both failed at the exact same time.
    It's also odd that my bluetooth scanner doesn't see the ECU.
    Also odd that I can't clear the codes even for a minute.

    I disconnected the battery for an hour with the same results.

    Those sensors are $125 each. I'd hate to replace them not being 100% sure that's what it is.
    They are old. I don't recall ever changing them in +250,000 miles. It's usually the post cat sensors that go.
    • Member

    MGarrison

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    Are all 4 identical, same specs, etc? Possible to swap the front and rear O2 sensors for a test? Any access to an alternate ECU?
    • Member

    steven s

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    Pre and post sensors are different.
    I'm going to see if I can swap from bank to bank.

    Come to think of it, my tech couldn't reset the CEL either using a pro scanner.

    Swapping an ECU isn't easy since I think it would need to be aligned with the EWS.
    But that may tell me if there is a wiring issue elsewhere.

    I've heard storied where the dealer was unable to reset the CEL too.
    I haven't gone that route.
    A service visit probably exceeds the value of my car. :(
    • Member
    • Technical Service Advisor

    charlson89

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    You could just purchase one sensor for now and replace it and see if you can clear one of the faults. Also make sure your obd1 port cap is on tightly if its not on all the way communication with modules will be intermittent or not at all. 250,000 miles on o2 sensors I'd say if they are bad you got your money's worth.
    • Member

    steven s

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    The OBD port cap was loose when I tried to use my Peake.

    I'm going to see if cleaning the port connectors helps next.

    Although I also used my bluetooth/Android scan tool on my Mini and now that is not seeing the ECU.
    I wonder if the ECU shorted out my BT adapter?
    • Member
    • Technical Service Advisor

    charlson89

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    If you can get to an auto parts store they usually have a scan tool you can use for free. Try that on your vehicle and see if it can communicate with your ECU.
    • Member

    steven s

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    Took another looksie.
    Precat O2 sensor loose. Tightened it.
    One exhaust manifold flange bolt either loose and another broken.

    I'm wondering if the bolts were broken when the last shop replaced my motor mounts?
    Or maybe they are just old?
    • Member
    • Technical Service Advisor

    charlson89

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    Really those normally don't even come out of the head, so to just all of a sudden come loose kinda weird. But if when they replaced the motor mounts they didn't support the engine right the force from the exhaust I have seen break manifold studs. ( I know because I did it on a E36 once :oops:) Any luck though after doing those repairs to clear the lights? Also did you figure out whats up with your bluetooth interface? Do you have a KIWI?
    • Member

    steven s

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    I haven't been able to clear the codes and my scanner still doesn't see the ECU via bluetooth.
    I connected the same scanner to my Mini and it doesn't see that one either. ??
    I see lights flashing on the BT converter though.

    The bolts that are broken connect the exhaust manifold to the exhaust. Not the head.
    I may end up living with it.

    What I'm concerned is I was going to have my oil suction tube replaced over the winter.
    I suspect that it is breaking. The oil pan needs to be removed.
    And at the same time tack weld the oil pump nut.
    But if the exhaust manifold needs to disconnect from the exhaust I'm worried about causing more problems.

    I think the only way to fix the studs is to pull the headers off.
    My motor has +250,000 miles on it now.
    Maybe I just let the oil suction tube break.
    It's only a problem on high g turns on track.
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    • Technical Service Advisor

    charlson89

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    On e46 and newer car the studs can be replaced by heating them up red hot and air hammering them out and installing a bolt and nut. I am not sure about older vehicles e36 but it might be worth a shot if they can they will have a flat head on the stud on the manifolds collector. Have you tired an other scanner recently to see if it will communicate?
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    alpinaman

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    looks like you might have a ground issue with the diagnosis connector ..
    can you read other modules ?
    • Member

    steven s

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    The Peake plugs into the round diagnostic port and my bluetooth adapters plug into the port under the dash.
    The problem may be with cheapo adapters. Two don't work and they don't work on my Mini either.
    Both see the OBD-II port but neither see the ECU.

    I may go ahead and buy a better OBD-II adapter.

    When I looked at my O2 sensor it almost looks like someone had spliced wires together.
    I can't get a good look in there on jack stands.
    • Member

    alpinaman

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    might have been hanging and the guy tried to put it all back

    i have a few scanners on one of my scanner that has bluetooth you have to connect the adaptor to positive and negative meaning it needed its own juice

    you can try this .. go to autozone or your local parts store .. buy a cheapy scaner that just reads and see if that sees the ecu ... if so return the scanner to the local parts store before buying anything bmw specific ..
    • Member

    steven s

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    Forgot about this thread.
    I had changed my 2 pre 02 sensors and was finally able to clear the CEL.

    Took my car into my tech to have the oil suction tube replaced.
    Get the car, CEL again. Seems to be the same exact faults.
    My Peake says both 02 sensors.

    I bought a new BT adapter from ScanTool which comes with OBDLink.
    There I am able to measure the voltages from the 02 sensors.
    They are both within range when the car is first started.
    Then once warmed up the voltage goes up and down on one of sensors.
    Almost in a pattern. When I'm over 3K the voltage seems normal.
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    charlson89

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    What are your P codes your are getting from these sensors? Also what voltages are you looking at the sensor voltage or the heater circuit voltage?
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    steven s

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    P0155 - 02 Sensor Heater Circuit Malfunction (Bank 2 Sensor 1)

    Sensor voltages from what I can tell.
    At idle they are both around .93v then one of them starts to jump around.

    When driving they both jump around.

    I'm suspecting an exhaust leak.
    When I do a quick blip I can hear a loud hiss. Or maybe it's my CAI?

    I bleed my brakes tonight and figured I'd disconnect the battery since the last time I replaced the sensors my battery was disconnected. I thought it might have something to do with the ECU.

    I never keep track of gas mileage but Friday I'll be driving close to 200 highway miles and will note my MPG.

    Added: Now I'm thinking maybe the exhaust leak that I had was hitting the O2 sensor and it damaged it? I believe my tech fixed the leak. Broken stud on the exhaust flange.
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    charlson89

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    Exhaust leak won't damage an O2 sensor but will cause faults.
    • Member

    steven s

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    That is certainly plausible.
    Would the leak need to be before the post sensors or could it be anywhere?

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