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post #1 of 3 (permalink) Old 11-30-2011, 10:38 PM Thread Starter
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1998 bmw 740 il


I have a 1998 740iL and I'm getting the following check engine codes: P0430 & P0420. Are these codes indicative of bad converters or what do you recommend as a cost effective approach towards resolving this issue?
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post #2 of 3 (permalink) Old 12-01-2011, 02:52 AM
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I would doubt both of your Cats have gone if either, more likely to be your O2 sensors, the thing with code readers is they just give the general fault and not whats causing it..you really need to get it diagnosed via Carsoft or INPA or you can always check your sensors:

Sensor 1 output should be very active and oscillate rapidly from approximately 0 to less than 1 volt. If the signal tends to show high voltage with little fluctuation, excessive unburnt fuel is reaching the sensor. If Sensor 1 shows low or no voltage, the sensor could be defective, or there might be an exhaust leak in front of or immediately behind the sensor, or there could be a lack of fuel delivered to the combustion chamber. If the sensor does not respond to a rapid accelerator kickdown, chances are the sensor is defective. If it does respond, an exhaust leak or lack of fuel is indicated. (The preceding test must be done after the engine and exhaust system have been allowed to fully heat up.)

Sensor 2 should show a fairly steady signal. It is not critical what the signal is, only that it does not oscillate as frequently as the front. If the signal is above 250mV, the sensor is fine. If it is below, check for activity by rapid accelerator kick-down or by raising the engine speed to approximately 2000 rpm. Any movement indicates the sensor is fine.


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post #3 of 3 (permalink) Old 12-01-2011, 03:45 PM
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