P0156 is a circuit malfunction code
for the driver's side rear O2 sensor, it is generally associated with a wiring problem.
The MIL eliminator could have a bad connector or wiring, or the MIL eliminator itself may be defective. It is possible the O2 sesnor is bad--more about MIL eliminators and how they work here
The only way to test is to get under there and monitor the sensor's output, both before and after the eliminator...
- 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum, Delta Force tuned,
Steeda UDPs, Ralco flywheel, RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.
New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq