ion_four

Can I add a resistor in series with the O2 sensor heater on a universal sensor to bring it up to the resistance (10-40 ohms, from about 6.5) and make it work? Would it be bad to just run it with 6.5 ohms of resistance?
here's why:
I'm in the midst of installing a turbo and since I'm having a custom downpipe made, I just bought the cheapest (NGK/NTK) four-wire O2 sensor at the store ($30 vs. $200 for the honda!!!) and figured it will work, since all sensors put out the same voltage and most have the same thread size and the tip of the probes are about the same...does anything else matter?

EE_Chris

The only thing I can think of that differs from OEM-Aftermarket, are the switching speeds....being that the OEM is typically faster.

Have I O'scope one of each, no I have not. I have however scoped my old one when it was heading south vs. the new one. The new one was faster indeed.

This was from the EnDyn board, where Larry stated that the Bosch O2's were better for performance, as they reacted slower thus allowing the engine to run a tad richer.

BigMoose

NO! You cannot add resistance in series with the heater. Doing that will cut the power to the heater. If you add an amout of resistance equivalent to the heater say 6 ohms external with the original 6 ohms of the heater, Yes you get 12 ohms but look what happens to the dissipated power. The equation for power is Watts = (voltage across the resistor**2)/(individual resistance)

So the original O2 sensor heater power would be 12**2/6 or 24 watts dissipated to heat up the sensor.

If you put 6 ohms in series with 6 ohms the voltage across the heater would only be 6 volts so 6**2/6 ohms or 6 watts. Thats only 1/4 the original dissipated power so the sensor will not heat up worth snot. So adding the resistor will get rid of the heater current fault light, but you will most likely get an ECM error based on sensor warmup time, if the sensor lights off at all.

If you find a sensor with too little heater resistance you can add some in parallel to get the resistance down to fool the ECM that the heater is not open, but you can't add it in series and still have the heater heat up OK.

Sorry. Look for one with a higher heater resistance. Take your ohm meter to the parts store....

Regards,
BigMoose

ion_four

Will the fact that the heater circuit has less resistance in this sensor make it take longer to heat up? So, even if I added the resistors it might still through a CEL in regard to the heat-up time...

the problem is that this was the only universal four wire in stock...would there be a way to use a 3-wire sensor? Do these just ground out in the sensor itself?...

EE_Chris

One of the black wires is tied straight to +V through a fuse. The other black wire [ground control] is tied to the ECU.

The green and white wires both originate at the ECU also.

So in a word...no.

ion_four

So, any suggestions for making this bugger work? If it's not gonna happen, I'll have to limp the car over there and hope I can find something.
Just a thought: Could I use a 2-wire and just put a 10 ohm 10 watt resistor between the heater wires? I suppose I'll just suck it up and spend the extra money on the proper sensor, but that seems like it might work, to me atleast.

BigMoose

Cheers to you! You jogged this old brain..... You got me thinking about the one wire, then the three then back to the four wire that you have. I said..to myself...yea, just hook a 10 ohm dummy for the heater, then the ECM will be happy about the heater problem. And if the sensor lights off then your good to go. Then I went back to your original idea.

You know ... your original idea is worth a shot. It will depend on how the ECM reacts to the slow warmup of the sensor. It may make it if you just need to drive the car once somewhere. You may get lucky! You may be able to dither the resistor value downward (say go to 4 ohms or 3 ohms) to satisfy both the "heater overcurrent alarm" and preclude a "sensor did not warm in time alarm".

Add 6 more ohms in series with the heater on the 4 wire that you have. The sensor will not light off as fast or at all. If its just slow to light, warm the car up then shut down and restart fast. The next cycle it might "think" it warmed up fast, since it is already warm and keep you in closed loop.

Darn ... here is your cheap solution. Place a dummy 10 ohm on the ECM to fool it that the heater is OK. Then wire 12 volts from the ignition switch (power when the key is in run position) thru a fuse to the heater on the 4 wire that you have. As they said in the movie...."that i'll do *ig, that i'll do pi*" ....sorry I was so slow on this one.

Thanks for keeping at it. I think You came up with a good solution.

Regards,
BigMoose

fixhondas

Get a Honda O2 or find a used one- universals generally suck.

ion_four

I was under the impression that honda uses Denso or NTK (NGK) sensors. This is an NTK. They all give the same readings, but apparently don't function the same. too bad.

I would use my old one, but it refuses to be removed. I even resorted to an impact wrench and it wouldn't budge.

fixhondas

An inline resitor will not allow the heater to work properly and you will probably get a sensor response code or you may fall in and out of open loop at idle. I have only seen Denso 4 wire O2's and NGK 1 wire O2's from Honda. Have yet to see an NGK 4 wire. You could try the inline resistor, I would make sure it is a ceramic one or it will probably burn out quickly.

BigMoose

When they are stuck to that extent I usually go to the heat wrench...oxy acetlene torch. Heat the low part of the hex, right by the bung. Get right on it with a wrench while the hex is still a glow. Surprisingly, some still work after this treatment.

Regards,
BigMoose