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BMW Fault Code – Oxygen Sensor Short To Ground – And – CCV – CVV Vacuum Hose M52TU

January 10, 2012

This answer is applicable for many BMWs in addition to the one listed below.

Q
car year: 2000
car model: 323i Wagon
Otto, First and foremost thank you for an excellent blog. There is a tremendous amount of valuable information here.
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I have for some time had a problem with my 2000 323 Wagon that pretty consistently reports the following oxygen sensor error the second or third time the car is started after they are cleared:
(Warm engine)
E3/E4: Oxygen adaption limit
97/9A PreCat Oxygen Sensor short to ground
CA/CB Oxygen Sensor Control Limit
The problems started when I replaced the CCV – Thanks for the nice videos! As part of the CCV job, I also replaced both intake boots and the throttle body gasket. I checked connectivity (and shortage to ground) from the Oxygen sensor plugs to the ECM – all checked out OK. Oxygen sensors are fairly new, I have no reason to suspect they are faulty. DISA valve is OK, no leaks. Car has no problems starting, no hesitations, and no rough idle. As part of my investigations I did find a cracked vacuum hose from the exhaust check valve to the vacuum control switch as well as from the vacuum control switch to the intake manifold – What a pain in the . to replace. But the error codes came back. When I changed the CCV I noticed my car has a small vacuum hose from the CCV connected to a small metal pipe on top of the fuel rail (front of engine). I replaced the plug on the CCV kit you sent me with a new vacuum hose and connected it to the metal pipe. A couple of questions: – What is this small hose for? I disconnected it with the engine running (idle) and felt no vacuum (Neither on the pipe of on the hose) – What is other end of the metal pipe connected to? (Small hose – checked on realoem.com but could not find an answer) Any ideas where my next efforts should be focused? Thanks.

A
First ;
The vacuum line that you mentioned is used on earlier applications that do not have the “fly by wire” throttle (mostly M52TU engines).  The vacuum line goes to the fuel pressure regulator at the front of the fuel rail, on these models (on other models the regulator is located at the fuel filter or pressure regulating valve, under the driver’s side floor).  If the application uses this vacuum hose, just remove the plug on the CVV’s vacuum nipple.  Otherwise, leave the nipple plug in place.

Now, on to your O2 sensor faults:

With the “short to ground” code, we should assume that this is indeed an issue. Have you checked each of the sensor wires to ground?

*  You noted that you have already tested the continuity from the sensor plug to the ECU/ECM plug.  This means that if one of the wires is grounded, it is not broken and we do not need to test for ground shorting (in the steps below) from both ends of the wiring.  Testing from the O2 sensor plug end (or the ECM plug) will be sufficient.

*  Unplug the sensor and unplug the harness plug from the ECU/ECM.

*  From the contact pins in the vehicle side harness plug, go from each pin to a good ground, with an ohm-meter or continuity tester. You should have no continuity on any of the wires.

Let us know what you find.  If there is a ground fault, the other fault codes will likely be due to this issue.

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