Bailhatch

I have a 4 wire o2 that has 7 ohms of resistance across the black wires (BK,BK,WH,GR) which I think is the heater part.

Are they not different because it is like a light bulb or a toaster, no polarity? Could I just add a 1-2 ohm 12v resistor to fool my ECU and eliminate the CEL?

big moose, you around?

onePOINTsix

yes you can, but you have to use some beefy resistors, like a 1W resistor from radio scrap will work fine

JimBlake

ummmm, more like 6 watts...

(that's based on 14.5v & adding 2 ohms)


Modified by JimBlake at 7:32 AM 3/2/2004

BigMoose

Yep just add it in series. If you add 2 ohms with the sensor resistance you stated it needs to be 3.5 watts, so make it a 5 watt. If you add 3 ohms you need 4.3, make it 5 watts, if you add 4 ohms you need 4.7watts, use a 5 or preferably a 7 1/2 watt or a 10 watt to have some tolerance for over voltages on cold days.

Cyphear

Are both black wires for the heater? I had to splice in some more wire in my O2 sensor and the wires got pulled off and I dont know which one goes where. I assumed both black wires were ground, and the other two were for the heater and the output voltage. Am I wrong?

StorminMatt

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bailhatch &raquo;</TD></TR><TR><TD CLASS="quote">I have a 4 wire o2 that has 7 ohms of resistance across the black wires (BK,BK,WH,GR) which I think is the heater part.

Are they not different because it is like a light bulb or a toaster, no polarity? Could I just add a 1-2 ohm 12v resistor to fool my ECU and eliminate the CEL?

big moose, you around?</TD></TR></TABLE>

Polarity makes no difference because the heater is just a simple resistor. But keep in mind that there are a couple of things you need to consider about just adding a resistor. First of all, you DON'T want to add just a 1-2ohm resistor. At the very least, you will not get rid of the check engine light. At the very worst, you could possibly do damage to your ECU since a 1-2ohm resistor could overload the heater control circuits in the ECU if they are not protected against this (and I am not sure they are!). You want to add a resistor of at least approximately the same value as the resistance of the oxygen sensor heater. And keep in mind that your figure of 7ohms might not be correct since you are getting a heater code! In any case, you would need a wirewound resistor capable of dissipating about 30watts (power dissipated = ((voltage)^2)/resistance). And this resistor will get quite hot. So keep it away from anything that can burn.

The other problem you could possibly have is a rich condition. On many cars with four wire sensors, the sensor is placed quite far downstream in the exhaust manifold/downpipe (as opposed to being close to the head, as is the case with single wire sensors). Since the exhaust cools quite a bit by the time it gets that far, the sensor might not work correctly without heat, causing a weak singal. This weak signal will fool the engine into thinking it is running REALLY lean or thinking the oxygen sensor is dead. If the latter is true, you will run a second code for the oxygen sensor output. And regardless, you will run rich.

The best advice I can give you is to replace your four wire oxygen sensor with a new one rather than trying band-aid solutions.

BigMoose

Clarification.... My answer was based on the assumption that you wanted to move the 7 ohm heater up to around 12 ohms....... I was putting the resistor in series with the 7 ohm oxygen sensor, as stormin matt said, 2 or 3 ohms is too low if you just replace the o2 sensor with it!

Perhaps clarify what you are actually trying to do. Replace the sensor and spoof the ECM with a resistor, or just move the heater ohmage up a tad to reduce o2 sensor current draw?

Cyphear

i found out the answer to my question in the integra service manual. both black wire are for the heater, the other two are for the sensor. Also, the manual says the resistance on the heater circuit should read between 10 and 40 ohms when measured. so maybe a 20ohm resiter would work if you are trying to bypass the circuit.

Bailhatch

Thanks a lot guys- it looks like you 2 posses the knowledge to help me out

what I am trying to do is to use a 4wire o2 from another car (ford NTK) in my honda simply for economic reasons. It is mounted about 5 inches after my turbine outlet.

So, as ypu guys assumed I am trying to run this 7ohm O2 w/o a heater CEL (which is the only code).

As far as overloading the ecu, that is why I am asking this question. I read a reply big moose wrote about doing this same thing but starting w/ a 3 ohm and he guessed adding a large enough resistor in series would draw too many amps (i think amps is right). So since I am closer to the 10-40 range than the 3ohm guy, will it work? Also, simply because of my electrical ignorance could I please get a specific part description of the resistor that should work? TIA!

JimBlake

If you put the new resistor in series with the heater, it will reduce the current thru the circuit. Because in series you add the resistance together. By just using the 7ohm heater you're pulling too much current, setting off your CEL.

Add 3ohms to get just inside the 10 - 40 range that your ECU wants. Max voltage should be about 14.5v, so the current thru that combination is 1.45 amps. Power in the additional resistor is I^2 R or about 6.3 watts. So you need a resistor rated at least that, or maybe 7 or 10 watts, whatever you find that's bigger than 6.3.

Even in series with the heater, the resistor will still get hot. Ever touch a 7 watt nightlight bulb that's been on all night?

If you can't find a 3ohm, use what you can find that's bigger. 4ohm will reduce the power of the total circuit, but the power in the new resistor goes up to about 7 watts. This also means that much LESS power goes to the actual heater.

cliff notes...
Your heater is already 7 ohms. Pick a resistor R so that (7 + R) is at least 10 ohms, but not too much bigger.
Current = 14.5v / (7+R) which is 1.45amps if you find a 3ohm resistor.
Power = (current^2) * R which is 6.3 watts if you find a 3ohm resistor. Your resistor has to be capable of handling at least that power.



Modified by JimBlake at 7:58 AM 3/5/2004

Bailhatch

thanks. do I need to get a wirewound resistor to make it reliable, or is that just if I was eliminating the o2 all together.

JimBlake

If you wanted to eliminate the heater altogether, you'll want a 10 ohm 25 watt resistor.

All you have to worry about is that it can tolerate at least 6.3 watts (or whatever) without burning itself up. You might find a ceramic resistor, but I guess those are just wire-wound resistors embedded in some kinda ceramic material with the wires sticking out the end.

It's not gonna be a little tiny thing like you see soldered onto a printed circuit board.

Bailhatch

picked up a few 10watt 1ohm ceramic resistors. I'll see if 2 or 3 of them does the trick.

Stewie

does the resistor have to be connected to the heater ground or can any ground be used?

JimBlake

Gotta be the heater ground. Heater power is supplied from the main relay, but the heater is grounded thru the ECU. It might be possible for the ECU to switch the heater on & off, but I'm not sure it actually does that. But the heater current has to ground thru the ECU so it can tell whether the 'heater' is working.

What are you trying to do, exactly? Replace the heater or adjust it's resistance?

Stewie

replace it so I can use wb sensor. I don't think there's a pinout on the ecu for the heater ground that's why I wanted to know if I could use another ground

JimBlake

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Stewie &raquo;</TD></TR><TR><TD CLASS="quote">I don't think there's a pinout on the ecu for the heater ground...</TD></TR></TABLE>On what ECU? My list simply calls it 'O2 sensor heater', but that's the ground side of the heater circuit. The (+) side of the heater circuit comes from the main relay, NOT from the ECU.

Stewie

wow! I didn't realize that! That clears it up a lot! Thanks again, bro