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BMW Oxygen Sensor

This bulletin applies to BMW 5 Series vehicles equipped with the N20 engine. The Service Engine Soon (BMW’s MIL) may be on, with DTC 118602 stored (oxygen sensor before catalytic converter, fine mixture control, exhaust gas after converter too lean).

This can be cause by an actual engine problem and/or DME software diagnostics. Perform the following test plan as recommended with the latest version of ISTA.

1. Electrical system troubleshooting of O2 sensor before catalytic converter.

2. O2 sensor heating troubleshooting.

3. Troubleshooting, function of O2 sensor before converter.

4. Mixture control troubleshooting.

5. Check lines and plug connections.

6. Functional check of O2 sensor heating after repair.

It is important to complete all of the above steps in the test plan and ensure that none of the following may be a cause of the fault:

1. Tank ventilation system.

2. Intake, exhaust and crankcase breather systems tight and without leaks (check with smoke tester).

3. Injection.

4. Air mass sensor (HFM).

5. Ignition.

6. Crankshaft and camshaft sensors.

7. Throttle valve.

If no faults are stored for any of the other components listed and the leak tests are inconclusive, replace the pre-catalyst O2 sensor (only if not previously replaced). Program the vehicle using ISTA/P 3.59.0 or higher.

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