Help for all diseases

Sat, 31 May 2008 17:55:07
By PCIDPUSA,

SENSOR BYPASS CIRCUIT

Electrical diagram

How to build Your Own Oxygen
Sensor Simulator!
The rest of the page shows how to build an oscillating signal generator with
just the right frequency and voltage to fool the ECU. It is based on classical
astable operating mode of 555 timer, so nothing revolutionary there. However we
spent few days of fiddling and testing to get the right behavior.

The parts will cost about $15 – $20 from RadioShack. It’s not that hard to
build if you have some experience.

Components: 
 

R2

R1	100 K Ohm
1 M Ohm
R3	100 K Ohm
R4	10 K Ohm
C1	4.7 uF
C2	22 uF
D1	1.7v@20mA LED
D2	1.7v@20mA LED

Hookup:

Power source	Ignition, or to the
Ground	One of the ground points or
OUT	(disconnect the O2 sensor wire)

Catalog part numbers from RadioShack stores:
(NOT for their online
system)
 

276-309	5mm wide angle red led 1.7v, 20mA
276-1723	The 555 programmable timer
276-1995A	The 8 pin socket for timer chip. It makes soldering safer and replacement easier
276-150A	Generic PC board
64-3052A	Pack of blue tap-in connectors
278-1225	Stranded wires (black, red and green)
270-1801	Small black plastic project box 3 x 2 x 1
272-1024	Capacitor, 4.7uF
272-1026	Capacitor, 22uF

Additional notes:
If you use different flavors of 555 timer chip or LEDs with different
parameters you will need to readjust the values of R4 and R2 to get the interval
and output voltage right.

Don’t attach it directly to the ECU right after assembly. Instead attach it
to the battery and check the output. You should get approximately 0v/0.7v
flipping about every 3.3 seconds when the car is not running, and 0v/0.9v when
the car is running. The current should stay below 10mA.

One LED should be always on whenever the power is supplied. Another LED
indicates when the output signal is high, so it should go on and off with the
signal.

When tapping the ECU wires, triple check everything before hooking up the
oscillator. The power source should read 0v when the key is removed, about 12.6v
when they key is at ACC and about 14.3 when the alternator is running. The
resistance between ground wire and the body shield of the ECU should be 0 ohms.
And it would be best if you run the car and monitor the voltage of the original
oxygen sensor wire before cutting it to make sure you have indeed got the right
one. The resistance between and ground is about 1.3 to 1.6 M Ohm.

The original sensor should still be dangling around, or plugged into the
downpipe. The reason is that ECU also monitors the resistance of heater circuit
inside the sensor. If you want to COMPELTELY disconnect it, you will need to
measure the resistance of the heater circuit and install the right resistor
Anyway, there is no need to do it if you just leave O2 sensor alone and
only intercept the oxygen signal wire.

Above testing and precautions will prevent you from frying the ECU and
spending major $$$$. Anyway, I assume no responsibility if you still manage todo so.