If the output from the ECU is an open collector NPN transistor as you have shown it, then it isn't an analog signal, it's a PWM digital signal. There are two ways you can read this on an Arduino:
1. Use a resistor to +5V and then an RC smoothing network to convert the PWM signal into an analog signal, which you can read using an analog input.
2. Feed it to a digital pin, time the HIGH and LOW intervals, then calculate the ratio of HIGH to HIGH+LOW. Easiest way is probably to use a resistor to +5V, feed it into a pin that supports interrupts, attach an ISR to that pin using mode CHANGE, and do the timing in the ISR.
I would use method (1) if the PWM frequency is more than about 1KHz, and (2) if it is lower.
btw:
(1) analog input readings on the Arduino go from 0 to 1023 (not 4096) because it is a 10-bit ADC
(2) a 160 ohm pullup resistor would give almost 5/0.16 = 31.25mA, not 5mA. A 1K pullup would give 5mA.