can someone explain these codes in detail?

 

Looks like you have misfire on cylinder #4 and bank 2 (front) O2 sensor fault, could be bad coil, bad spark plug or O2 sensor.

 

i replaced the coil and plug, witch sensor and where would it be located?

 

Bank 2 sensor one. This is the sensor between the engine and radiator.

Symptoms of a P0154 code may include:
*MIL (Malfunction Indicator Lamp) illumination
*Other codes indicating rich or lean condition may be present
*Poor idle, won't idle
*Misfire at idle or at highway speed
*Engine may blow black smoke at tailpipe
*Fuel economy may decrease
*May start and stall

Potential causes of a P0154 code include:
*Faulty bank 2,1 Oxygen sensor
*Holes in exhaust near oxygen sensor
*Short to voltage or ground on signal circuit
*Open or high resistance in signal circuit
*Wiring harness chafing/rubbing on exhaust components
*Water/oil intrusion at O2 sensor connector
*Broken lock or loose terminals on O2 sensor connector
*Oil/coolant fouled oxygen sensor

Read more at: http://www.obd-codes.com/p0154
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How many miles are on the vehicle/engine?

Is the car still shooting gas out of the spark plug hole when you turn over the engine?

Depending on the vehicle's mileage and service history, you may want to consider replacing both upstream O2 sensors.

Here's a picture of the (left bank) O2 sensor plug.



Here's a picture of the left bank O2 sensor.



Removing the O2 sensor.



O2 sensor removed



The old O2 sensors.

 

wow those 02 sensors look quite worn out!

 

They had been in use for roughly 150,000 miles. They must have grown tired and lazy over the years. I remember getting both the O2 and KS codes. Since that was Max #1 and I didn't know about the KS ghost code at the time I was surprised to see the KS code disappear after replacing the O2 sensors. The new NTK O2 sensors perked up around town performance and improved MPG.