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  #1  
Old 09-08-2014, 12:58 PM
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2002 e320 sedan O2 code help

Hello everyone. I need some assistance on this car. I have 2002 e320.

There were 3 pending codes intiallly- p0154 (o2 b2s1 no activity), p0155 (b2s1 circuit malfunction), p0135 (o2 b1s1 heater malfunction).

I changed both front o2 sensors simultaneously with new direct fit o2 sensors.

I cleared codes, started car, it warmed up went into closed loop. Drove about 10 miles codes came back.

I cleared codes, tested o2 plug connection is good. Then I used DMM to test heater circuit of o2's- when key cycled terminal #1(red/grn) of both o2 sensor(s) gets 12v B+. The number #2 terminal of o2's plug (heater ground) is .4kohms with engine ground-I assume this is ok. The internal heater resistance of both new o2 sensors are 13.6 ohms exactly.

When I look at live data on scanner, I can see both o2 sensors generating a flucuating signal. So it doesn't appear to have problem.

What is weird is the codes are only generated if I turn key on and off without starting the car. They aren't coming back yet as confirmed just pending.

Anyone have any ideas??? ECU maybe????

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  #2  
Old 09-08-2014, 05:07 PM
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Join Date: Aug 2014
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update on problem

I disconnected the computer. All wiring terminals looked ok. I used pin out diagram and tested the continuity between corresponding computer pins and the pins at the o2 plugs- everything has less than 1 ohm.

So my conclusion is= if it comes back the codes, has to be internal ECU?

Can any one confirm or dis-confirm my deductions?


Thanks for your time.
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  #3  
Old 09-08-2014, 11:51 PM
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codes are back!

So codes are back. Computer??? Any way to use a used computer and program it?

Any experience out there?
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  #4  
Old 09-09-2014, 11:06 AM
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Join Date: Jul 2004
Posts: 187
I guess problem is something like a bad injector or coil. That could possible trigger a faulty O2 code.
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  #5  
Old 09-10-2014, 01:17 AM
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injector or coil?

Can you elaborate as to how this trips a o2 heater code?
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  #6  
Old 09-11-2014, 02:16 AM
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Location: Seattle
Posts: 1,947
Computers are notoriously bad at telling you what is wrong with them. They are good at knowing that something is wrong, but bad at being very accurate about what it is. I searched on those codes and some people are saying look for a vacuum leak.

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