W123Mech

03 Civic EX. Bought the car as a non runner to build for my grandson, so I know zero history. Let's get to why I'm here.


Car runs fine, except a CEL. Clear code, comes right back.
Hook up scanner, which shows P0141. No big deal, replace sensor.
Buy Denso sensor, replace. Still shows code. Hmm.
Hook up scanner, see that the rear sensor voltage is not changing. Measure voltage with KOEO, it's good. Measure ground (why do they get a switched ground from the ECU?), and it's not there with KOEO. This explains why the voltage is not changing. Cut the ground wire, and splice a ground in there. Hook up scanner. Voltage is changing like it should. CEL still present for P0141. 02 sensor is reading 10.9 ohms in the heater circuit cold.


My suspicion at this point is that the ECU is not reading the inserted ground because the ECU is not the one providing the ground. If it is the ECU, I have no idea how long it's been that way. The car was sitting for about 8 months before I bought it.
Thoughts?

ezone

That is correct.

I don't have my O2 sensor resistance notes on this laptop.
Was the original sensor a Denso?

Much of the ECM controlled switching is accomplished by turning grounds on and off. That's a basic for most from any manufacturer.

KOEO probably won't turn on the heater circuit because the engine is not running, therefore it's not needed.

Heater should turn on with or shortly after KOER. Again, the ECM controls the ground to the heater.

Code is set at 5 seconds of fail.
Code is set when amperage of the heater circuit is above or below the threshold (amp load), as determined by the ECM.

You may need to erase the fault code before attempting to check anything, every time. Sometimes the presence of a code will cause the ECM to quit trying to run the component.

W123Mech

First, thank you for your assistance. I'm pretty sure the original 02 sensor was installed. I no longer have it, since I thought this would be an easy fix. It was pretty well destroyed coming out of the exhaust. Now welding a bung in there.
These are things I've read so far. KOEO does send the voltage down, and is supposed to switch the ground Also, the heater should be 10-40 ohms, but 40 seems sort of high. Perhaps Densos are more around the 10-15 ohm range. I can't test anything for a bit. I have the transmission out again to redo the main seal. The housing is chipped, like someone took a screwdriver and beat it in there to get the old seal out.

I can see where this is heading. New ECU, ignition, etc... This car just likes to suck money out of my wallet.

ezone

Notes from checking an 05 Civic:
05 civic rear O2 sensor, original= NTK 15.6 ohms hot
" used NTK 15.5 ohms cold @65ish
" new A/M Denso 13.4 ohms cold @65ish F


W123, you a Daimler tech?

W123Mech

Not a paid tech, but owned 10 of them and a W126. All diesels. Love the simplicity.


It looks like my new 02 sensor might be bad. I might take my leads up to the Advance to measure theirs. They have a new one in a box that I bought and returned the same day after I found the non ground issue.


There was one time I cleared the code, and it stayed off for the next 10 minutes while the car was running. Started the car about 15 minutes after that, and the code came right back.


If I need to replace the ECU, I know I need the key as well. The ring that goes around is just the RF transmitter, so I shouldn't need that I don't think. I've only swapped ECU and key with my Focus, not sure on the Honda.

ezone

Your 10.x resistance might be awful close to the borderline/cutoff, can you find one closer to 15 ohms?
(Honda no longer publishes resistance specs for these, dangit)

You're dealing with the REAR sensor, correct?

The ring around the ignition is the immobilizer control unit.
A replacement ECM/PCM must be programmed to accept that immobilizer CU and all keys, before it will allow the engine to run. Programming is done on-board, with a scanner. No off-board programming can be done that I know of, for this.

If you go used, you can probably get a matched set of
PCM/Immobi/Column lock assy/keys from a donor car.....but there are caveats with this too. .

W123Mech

Yes, dealing with the rear sensor.


If it needed it, I was going to grab the keys, computer, and column lock. Now I know I do need that ring as well.. Heck, I might have had to replace that ring also on the Focus, it's been a while. I saw one complete set on the Bay, but I'm holding off buying something until I can prove something bad. Why throw parts at something without properly diagnosing it first?


Since I can't work on the car for a bit, I might pull the ECU out and open it up to take a look. Long ago, I would look for a transistor that might have gotten hot, but I fear those days are in the past.

ezone

Got a test light? Assortment of 12v light bulbs?
Ohm check a few bulbs, find one that's close to the resistance spec of the O2 sensor.

Connect light bulb to the heater circuit.(sensor disconnected)
Have someone start the engine, see if bulb illuminates AT ALL--that would confirm the PCM can supply ground to the heater.


It may shut the circuit off and set a code again because the resistance of the bulb changes a lot when the filament heats up.

I did find an amperage spec range for the heater circuit of 0.2A-1.7A. Anything outside that range is enough to set the fault code.

W123Mech

I can find a 15 ohm resistor, and wire it in series with a 12 volt light easy enough. I just got some grain of wheat bulbs to fix my Mitsubishi radio illumination, so I have plenty left. I'll let you know what I find. Still waiting on the main seal housing.. and waiting... and waiting...

ezone

Um, I don't think that will work unless the total is still within the spec range..


If you wire them in series you have to add the resistances together (bulb+resistor=total resistance) which may be too much.

W123Mech

True. Just measured a bulb, and has more resistance than I thought. On a side note, the rear main seal has been replaced, trans is back in, and the car is drivable. Now I can concentrate on the 02 sensor issue. This should be the last issue with the car. I've replaced so much, it's hard to list all of the parts.

W123Mech

I finally had time to do some more testing. Hooked up the test light. Started car, light flashed for 5 seconds and went out. At the same time, the CEL illuminated. So, it looks like the computer is trying to send a ground, but the resistance is off so it quits. Just like you said. I tried it several times. Here is my procedure. KOEO, clear codes. No test light activity. Start car, test light flashes. 5 seconds later, test light quits flashing, CEL illuminates.
I am bringing my multimeter to Advance, and measuring their Denso 02 sensor before I buy one. I may have bought one that was just below the threshold for this car, as you suggested. I'll let you know later today what I find. Thanks again, it's nice to be able to throw ideas around without the bashing that goes on in a lot of forums.

Another update.. For some reason the 02 sensor is now reading 4.4 ohms. Yep, time for a new one. I'll keep you posted.

W123Mech

so what I thought was a Denso (it's been a long while since I bought it) 02 sensor was probably a no name. Installed the Denso 02 today, cleared codes, started car and everything is fine. Watched the voltages on the scanner, and both voltages were changing as they should. Lots of lessons learned here, first is not to always trust what you read (KOEO providing ground) on the internet.
Thanks ezone, gave you a rep.

ezone

Thanks, and thanks for the update

Situations like this are why some of us strongly recommend certain OE and OEM parts.

W123Mech

Normally I would use Denso,, so not sure why I did not on this one. For my CL, I got all Honda timing belt parts, Koyo pulleys, etc. Honda likes only quality parts, and that's usually what I throw at it. Just glad to give his car back, so I can get my CL back.

W123Mech

Drove it 100 miles to deliver it to the grandson. No issues besides a small oil leak. Looks like it's coming off of a black box behind the engine. Anyway, get a text when we got home. Check engine light came on as soon as he started the car. WTF is with this car.. It's like it does not want to get back on the road. If you knew how much I've done to it, you would surely understand the frustration level. Told him if it comes on again, take it somewhere to get it scanned for free. I'll interpret them and see what it needs. Lucky for me, if it needs work, that's more bonding time.

ezone

Post back when you get the code numbers

Have kid disconnect a battery cable to erase engine codes, then see if it comes back? (might need the radio unlock code if you do this)

W123Mech

Good news. He disconnected the battery, and code has not returned. Just got three recalls done, new tires, and passed state inspection. He loves this car. The only thing left is a small oil leak. It looks to me like the PCV valve is clogged and getting pushed out of the black box on the back of the motor. I see most new valves are screw in type, so I may have to get a box from a junkyard and get a new PCV.

W123Mech

And the code returns.. This is awesome... I swear this car will kill me. Oil leak turned out to be a large oil leak, I suspect from the o ring on the oil pump. Got that replaced. Replaced the cat due to the old one being a POS, and the P0141 code is still there. I've about had it. Heater on the O2 is 15.8 ohms, which is right where it's supposed to be. Everything keeps pointing to the ECM that is not providing a ground. I've found a few pinouts, and they all say pin 14 on Connector E is the black and white wire going to the sensor. Well, both Civics I looked at do not have a wire hooked to pin 14. So, no help there.

ezone

I think you found diagrams for the non-vtec d17a1 engine.


EX (vtec, d17a2) Secondary O2 heater ground control at the PCM is terminal E6, wire color at ECM is black/white (to white wire on sensor)
Power to sensor heater comes from fuse 4 in dash fusebox, black/orange wire (to white wire on sensor)

DarthBob

I had the same problem.
Bought a new sensor off the shelf (Denso) and the resistance of the heater was 3.5 ohms.
It needs to be between 10 and 40.
Take your meter with you and check the 2 wires that are the same color. between 10 and 40 is good.

pullmyefinger

I have been reading thru your conversations because I have the same probem with my Civic. Ebay does have (paper) shop manuals that you can buy for under $40.00 (I just bought one and it is worth the money). '01 Civic EX 4dr sedan D17A2 engine, 1.7/4cyl..

I am getting the P0135 and -0141 codes and I hope this helps me. Just bought up and down denso sensors for it and still have the CEL...