hi,
i have a 2001 s2000 throwing 2 codes stating that the heater circuits for both of the o2 sensors are malfunctioning. i only have an upstream o2 sensor and i've switched it out with 2 different new sensors, 1 universal and 1 make specific. upon resetting the ecu, the code returned within seconds of the car running. what other issues could i be having? there's a fuse for the heater circuits and i've switched it out as well. the car seems to be running just fine, but i'd prefer to get this taken care of. thank you for your time.

 

you jumped the gun. first check that they are getting voltage. It may be that both get power from the same fuse and the fuse is blown. You should have checked resistance on the heater side of both sensors to comfirm that they are faulty.

 

ok, i'm kinda new to the wonderful world of multimeters. that'd be ohms, yea? and what prongs would i test?

 

ohms is resistance. you want to check for voltage. most sensors have 4 wires. one ground and three that have power if i remember correctly.

 

so just check for 12v on all 3?

 

 

its the same for all o2 sensors. check the whites

 

oh, awesome. i'll post results tomorrow. thank you much.

 

ok, my heater wires for each plug are pairs of black/yellow and black/white. on each plug, the black/whites are showing no voltage but i cant find a break in the wires anywhere

 

tried a second harness i had lying around and the same wires were dead. burned something out in the ecu?

 

you would check resistance on the o2 sensor itself on its heater circuit to determine that the heater side of the o2 is open or not.

 

if it isnt getting voltage at the harness plug, why check that too?

 

Heres a video from eric the car guy explaining O2 sensor diagnostics:
Hopefully it can help a bit, Good luck

 

Power for the heated O2 sensor(s) is supplied by the fuel injector relay in the PGM FI Main Relay on most Honda/Acura, some are powered directly from a fuse, only one of the leads will have power on it.

In your case, it is most likely the black/yellow.

Sorry, I do not have a wiring diagram for the 01 S2000, but regardless, if you unplug the O2 sensor only one of the leads should have power, if not, either a fuse is blown or there is a connection problem. 94

 

ok, so the sensors are getting power to the heater circuits since the black/yellows are getting 12v. so why am i getting the code? i know all 3 of these sensors can't be bad.

just tested the resistance of the heater wires on one of the sensors i tried and it showed 13.3 ohms

 

Just run new wires, but make sure it's shielded wire(these wires are sensitive to radio interference)...use 16 gauge and make sure to ground the shielded portion on either side of the cable...just cut back some of the shield and put a butt connector on it and run it to ground.;

 

but if i'm getting 12v on the black/yellow, doesn't that mean that it is grounding? getting power and proper ground to the heating element in the sensor but still throwing a code saying it's malfunctioning. sensor shows proper resistance across heating wires. tried 3 different sensors with the same results. tried a different engine harness with the same result. ie, the problem does not appear to reside within the wiring from the ecu to the sensor.

 

Again, the power, [12V+] is supplied by either the PGM-FI Main Relay or direct from a fuse, the ground is supplied by the ECU/ECM, check for ground or check continuity of ground lead between sensor and ECU/ECM or pull the O2 turn on the ign. and see if it heats up 94

 

i used the plug ground, ie the ecu, to test the black/yellow voltage. i'll check to see if it's heating though

 

Did you do that test with O2 sensor plugged in or unplugged?

If unplugged plug it in and do it again or use a 12V test light, [not LED type] so there is a load on the circuit. 94

 

how would i use a voltmeter to test it when it's plugged in? the sensor isn't heating up btw

 

You need a very small pin of some sort that is magnetic...slide it through the wire til it bottom out and gives a reading. This is called backprobing.

 

Not through the wire, along the wire/lead into the back of the plug, if you do punch a hole in the lead, [damage insulation so air/moisture can get at the wire itself] the wire inside the insulation will corrode.
Even when back-probing properly it is a good idea to have a can of liquid electrical tape so you can "dab" the damaged area with it to seal out the air/moisture. 94

 

back probe shows 12v to both the black/yellow and black/white when plugged in

 

Then there is no ground, you are reading 12V on the black/white through the sensor. from the black/yellow. 94