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????