Using light sensor with Arudino Motor Shield

Hey Forum,

Problem: could not achieve same analogRead value with Arduino Motor Shield as compared to UNO.

When I connect a light sensor to arduino UNO and uses analogRead, the value makes sense and it works perfectly (just like in the starter guide). The value is about ~90 and when i cover up the sensor it goes to very low ~2.

But, when i added an arduino motor shield and I plug in the same configuration on the shield bypass pins, the analogRead value becomes weird. Under the same lighting condition, the value stays very consistent at 16 and when I cover up the sensor it drops to 15 and sometimes i does not even drop and stays at 16. I have tested the configuration and wirings, it works perfectly on a UNO without the shield.

I want to read the light intensity and use the shield to run a motor according to the output from the sensor.

Does the addition of shield/usage of bypass pins, causes the sensor to operate beyond its normal operating condition?

Board: Arduino UNO rev3
shield: Arduino Motor Shield rev3
light sensor: the one from the starter kit
Resistor: 1k ohm

try A4 or A5
take a look at pin use in the schematic