ECM is throwing a code P0135 after a shop replaced both sensors and performed a tune-up. I am not taking my car back to that shop because they have demonstrated that they are a bunch of clowns. (Another topic). The point is that the sensors are new. Resistance on across the heating element is around 4 ohms, which is low, according to the Mitchell procedure I got my hands on. That procedure prescribes a resistance of 10-40 ohms. I checked another new sensor at the parts store, and it came up at 9 ohms, not in range, but not as far out of range as four. Neither side showed conductivity to ground.

The terminals driving the element do not show voltage relative to each other, but the yellow-black wire in the harness did show battery voltage relative to ground, which made me suspicious of the low side wiring being open. I pulled up the floor and checked the harness at the computer. With the plug off and checking connector (not the computer), a voltage did appear across pins 6 and 10, 6 being the orange/black wire running to the sensor plug, and 10 being ground. The sensor was plugged in at that time, which indicates to me that the voltage was making it from the yellow/black, through the sensor and back to the connector I was checking, not being stepped down because I had the circuit open and no current should have been flowing.

Does anyone happen to know how the heater circuit functions at the ECM? Does it pull pin 6 to ground to turn the heater on, then let it float when it is not needed?

Is there someone I can have check the computer for less than the price of buying a used computer off ebay? ($85-$100)

Is the 4 ohm indication REALLY a clear indication that the sensor is faulty?

On another topic, What is the sticky goo that holds the hood gasket in place?

 

I poked around a bit and found this article on O2 sensors:
http://www.asashop.org/autoinc/dec2002/mech.htm

It seems to indicate that a 4 ohm reading might not be wrong, I may want to try it again with the engine hot. It also mentions several methods for driving the heater. I have no Idea which one is used in this case.

BTW, This is a 97 Accord LX, Computer is a 37820-P0J-L11.

 

got the same problem

 

Its possible to get a bad heater sensor from the factory. You should take a look at the harness going from the sensor to ensure the wire isn't frayed or broken. That would account for a bad reading.

 

Bought a used computer on ebay. That did not solve the problem. The harness seems to be good all the way back to the computer, but changing the computer did not help. Next step I suppose is to try a sensor that is closer to being in spec according to mitchell.

 

I have seen 2 O2 sensors come up with 4 ohms across the heater. They were both of 4th gen ex's, the ones underneath the oil filter. They have unconventional heads on them, they dont have the cheese grater thing going on. These both were used, but they both checked 4 ohms on the money, and the others spares i have all tested out in the 15 range and they looked like the cheese grater cylinder, these went in the exaust manifold right in the engine compartment of 4th gen lx and dx's

I would say your issue lies in another place.

 

The most suspicious thing to me is that when the ignition is on, the heater circuit only registers voltage against ground, and not against it's own return. The strange thing is that the return rings out all the way back to the computer. I'm going to verify that the #2 sensor shows voltage against it's own return, but with two computers doing the same thing I'm out of ideas after checking that the contact at the computer is actually engaged. Can anyone else verify that proper operation has 12 volts on the heater circuit against it's own return? These are the bottom two pins when the clasp of the sensor harness connector is up.

 

I just went through this nightmare a few weeks ago: https://honda-tech.com/forums/honda-accord-1990-2002-2/code-43-fuel-supply-system-2137671/

I don't have good things to say about Bosch sensors. To test the heater circuit, the car and exhaust should be warmed up as resistance increases with temperature. 9 ohms cold in the box sounds good to me, that should increase to at least 11 ohms warmed up.

 

Results of checking sensor #2 are that it's harness behaves exactly the same as #1, i.e. The hot side won't read a voltage against the return, but it will against ground. After reading this procedure again carefully, I've decided this it the correct state, as the successive steps after a positive reading between those pins amounts to checking to see if that wire is shorted to ground. Sensor #2's resistance is 15 ohms, which puts suspicion back on the sensor heater in #1. I'm going to see if autoZone has a Denso sensor.

 

Well, autozone didn't have a denso sensor in stock, and the checker across the street had the bosch version for $20 less. I brought my multimeter with me and checked the resistance across the heater, which came in between 8 and 9 ohms. Still not in the range specified, but after the clerk re-assured me that I could return it if it didn't work under the warranty, I went ahead and bought it.

Along with the sensor, I also bought an offset o2 sensor wrench, which I really like, it's the best I ever used and I don't think I'll ever go back to an open end or even the socket type slotted o2 wrench.

Anyway, I brought the new sensor home and was able to replace the sensor while the manifold was still hot. I cleared the code and started the car. Normally, the code is thrown within seconds of starting the car, but nothing came. If I don't post again to this thread, that means that I ran the car again after letting it cool overnight and that the heater is working I can claim victory and start looking for someone to buy the extra computer I now have.