Have BMW Z3 3.0i roadster (Manufactured in 2000) with fault codes 76, 99 and 6F. Garage has supposedly replaced faulty oxygen sensor but tickover is still erratic although for most of the time car runs perfectly. The fault occurs when foot taken off accelerator pedal and revs increase and lower before settling down to normal idling speed. Also seems to happen when I reverse. Any advise please? Mike B

it is normally the HO2S ( heated oxygen sensor) in the exhaust manifold before the cat converters
That unit reports the exhaust gas composition to the ECM which adjusts the mixture according to the MAF/VAF sensor readings
Add to all of those the ambient temp sensor and the BARO sensor and you have the system that adjusts the air/fuel mixture
how to fix
have the fault codes read and replace the faulty sensors

Possible causes
- Oxygen sensor harness is open or shorted
- Oxygen sensor circuit poor electrical connection
- Exhaust system leak
- Faulty front or rear (pre-cat or downstream) oxygen sensor


what it means Harness is open or shorted It means that the wire(s) connected from and to the component (sensor, solenoids, actuator, etc.) is either open (cut, broken, disconnected) or shorted (touching other wires, components, body). "Open" and "short" are common electrical terms. An open is a break in a wire or at a connection. A short is an accidental connection of a wire to ground or to another wire. In simple electronics, this usually means something won't work at all. With complex electronics (such as ECMs or PCMs) this can sometimes mean something works, but not the way it's supposed to.
Circuit poor electrical connection It means that the component (sensor, solenoids, actuator, etc.) connector is not fully connected or is disconnected. Before replacing any components, try fully disconnecting the connector, reconnect and test the system or component again.
Faulty or Failed component It means that the component it's more than likely the cause of the code and that needs to be replaced
Engine mechanical problems When a code list as possible causes an engine mechanical problem, it means that the problem is not caused by electronic component, but rather by a mechanical component such as pistons, valves, mechanical pump

P0140 BMW P0140 BMW - O2 Sensor Circuit Low Voltage Bank 1 Sensor 2



Possible causes - Faulty Rear Heated Oxygen Sensor Bank 1
- Rear Heated Oxygen Sensor Bank 1 harness is open or shorted
- Rear Heated Oxygen Sensor Bank 1 circuit poor electrical connection
- Inappropriate fuel pressure
- Faulty fuel injectors
- Intake air leaks may be faulty
- Exhaust gas leaks

Replacing the Rear Heated Oxygen Sensor Bank 1 usually takes care of the problem
http://engine-codes.com/p0140_bmw.html

You can in most cases repair this by cleaning the engine throttle valve and the idle speed control valve using a product called CRC Spray Throttle valve cleaner. Spray the cleaner into the air intake of the engine with the hose removed from the throttle body, the engine will try to stall so hold up the idle speed manually. Once you have used up about 1/2 can of the cleaner stall the engine out while spraying and turn the key off, disconnect the negative battery cable for 5 minutes and then reconnect and drive the car for a about 25 miles of varied driving modes. If this doesn't cure the problem you may need the fuel injectors professionally cleaned by the dealer service dept.

There is no one fix works on this O2 sensor code
P0170 - Fuel Trim Malfunction Bank 1
Possible causes- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection

We guess DTC P0151... essentially the same as P0136 and P0137 and P0131, a P0151 code refers to the first oxygen sensor on Bank 2 . P0151 means the O2 oxygen sensor's voltage remained low for longer than 2 minutes. This, is interpreted by the ECM as a low voltage condition and sets the MIL. Bank 2 Sensor 1 is located in front of the catalytic converter.

There may be no visible symptoms to the driver, other than the MIL (Check Engine / Service Engine Soon) illumination.

A code P0151 may mean that one or more of the following has happened:
Faulty o2 oxygen sensor
Short to voltage on O2 signal circuit
High resistance or open on O2 signal circuit

Possible Solutions:
Replace faulty sensor
Repair short, open, or high resistance on o2 signal circuit

Isn't there a rear sensor by the catalytic converter also?

bank 1 will be whichever side cylinder 1 of your engine is and bank 2 will be the opposite side. It's named bank 1 and bank 2 so that no matter how the engine is laid out, bank 1 is always on the same side as cylinder 1. I cannot say whether the right hand or the left hand one will be bank 1 as I do not know where your cylinder 1 is. The garage should know

BMW engine light

Comes on if DME engine management system self diagnostic fault detected. Will stay on until codes are called up and memory erased.

With OBD read the code as follows. Turn on ignition key, press accelerator pedal to the floor five times within 5 seconds. The check engine light will remain on for 5 sec , blik off, come on for 2,5 sec, go off for 2,5 sec and fault code will begin to flash. If more than one fault exist 2nd fault code will be separated by 2,5 sec pause. after fault codes there will be a 0.5 sec flash and light will remain off. to read codes again do procedure again.

Canceling of codes. make sure fault code is present (short blink and light goes out for long period), depress throttle pedal for at least 10 sec. read fault codes again and check for code 1444 (no faults stored.)

Check also the following, fuel pump, oxygen sensor, fuel injectors, engine coolant temp sensor, idle speed control valve, mass airflow sensor and too many other things.

If there is a code for the Air Mass Sensor I would recommend replacing it. Also a common problem is the intake cam sensor going bad and not giving a fault but will cause the car to stall.