rcode

03 civic ex 1.7 litre vtech automatic with 268,000 kms good compession ...having poor mileage issues but lots of power and driveability is good . had a aftermarket cat put on it about 5,000 kms ago because the old one had cracked and rotted out . noticed today on my scan gauge that at cruising speed fully warmed up the o2 sensor is running in the closed loop but when i let off its in the open loop mode i never noticed it before is this normal for these cars . i always thought once they were warmed up it stayed in one mode but im not sure. thanks lee

ezone

Normal and correct. You are seeing "deceleration fuel cutoff" in action registering as 'open loop' and you should also be able to see it on the primary O2 sensor voltage as extremely lean (zero volts or very close to it) because there is no fuel being injected at that moment in time.


Wide open throttle acceleration should also show as open loop, along with primary O2 sensor showing above 0.80v during the event (if sufficient fuel is delivered).

rcode

if i decide to replace the 02 sensors are there any brands other than honda i should buy my local parts store sells nkg?i think ... everything is working pretty good other than the 18-20 mpg. i got the air out of the cooling sys now with the new honda rad cap and honda thermostat its running bout 182 deg f at highway speeds and heat out the vents at idle but will keep a eye on it for the hg prob if it arises.and again thanks for your input ezone ps anything else mileage wise i should look for while im into it?? thanks lee also what would be the engine designation for this car canadian 2dr 1.7 si d17a2???

ezone

Look at the ORIGINAL sensors, see what brand each one was (you may have to clean rust off to find a brand name). OEM sensor brands were Denso and/or NTK.
Replace each sensor with matching brand, whatever it came with. Once you know what brand, you can go to that manufacturers website to look up your exact sensor part number.

No discount cheapos, and no Bosch.

IDK. Do a thorough checkover and fix whatever is broke or worn out?

skipcfd

I have an 03 Civic EX and I have a check engine light on, and it's reading:
P0141 - Powertrain
O2 Sensor Heater Circuit (Bank 1 Sensor 2)
After seeing this, I did a basic Google search, and I came up with it's the downward stream 02 sensor. I replaced, and reset the code, and after restarting the motor, the check engine light came on with the same code. I can not figure out why this is happening. Does anyone have any experience with this problem?
I have noticed that the mileage is getting worse. Also, I had something happen as I was pulling out of a parking, spot. I went from reverse to drive, and as soon as I accellerated, the motor acted like it was going to die, the RPM's went down like the motor was choking, and then it just suddenly took off before it died and had no issues after that.

ezone

What brand was the original sensor?
What brand did you install?
Where did you install it? (possible wrong sensor was replaced?)

Did you ohm test the heater circuit of the original to verify it was faulty?

skipcfd

I installed a Densco sensor, and no I didn't verify the other one was bad. A friend at work did check to see if power was getting to the sensor and it was. We replaced it anyway, because it wasn't overly expensive and I had it handy. But when we installed it, cleared the code and started the motor, the check engine light came on, and had two codes, and said the upward and downward sensors were bad. So, we looked under the steering wheel and replaced the number 4 fuse, because it was blown. As soon as we did that, cleared the codes again. the check engine light came back on, and only said downward sensor again.

ezone

So....SOMETHING caused the #4 fuse to blow...and that fuse supplies power to:

Front O2 sensor
rear O2 sensor
ELD
Cruise
EVAP solenoids
VSS
and the alternator

Something somewhere caused excessive current flow and blew the fuse.

Did it set codes for any other items that share the same fuse?

Now that the car has reset the fault for the rear sensor, has it blown the same fuse again?

Power is only HALF of the circuit. What about the heater GROUND that also must be present in order for the sensor to operate (while the engine is running)??
That ground is controlled by the PCM.....A good service manual will have circuit troubleshooting info.

Also note carefully: Correct heater circuit resistance is critical, if it is not in spec the computer flags it as a fault right away and sets the code. I'd ohm check both and compare old vs. new just to make sure they match (IF the old one is still good)

If any wiring problems are present between the PCM and the sensor, that can cause codes too. See the wiring diagram link below.


I have a note saying rear sensor heater spec is 10-40 ohms,
and a known good and working rear O2 sensor heater in an 05 Civic measured 15.6 ohms hot.


Here's a link to a post with the wiring diagram for the O2 sensors in it:
https://www.civicforums.com/forums/3...ml#post4713384



Did they sell you the correct Denso sensor? Check part number on the Denso website here:
http://densoautoparts.com/find-my-pa...icle-selection

skipcfd

I appreciate your help. I will try what you suggested.

Also, do you have any experience why the airbag light will stay on even after the airbags were replaced d/t recall?

ezone

Plenty of experience.

If the light was on prior to them doing any work, the recall will not repair the problem.

If the light was NOT on prior to their work, then it's a good bet that someone made an error during the work (it happens sometimes) and caused the warning light (and fault code)

You can take it back to the dealer who did the recall and say the airbag warning light has been on (ever since?) and ask them to recheck their work.

After they tell you it is not related to the work they performed, you can have them diagnose the problem (probably for a fee, of course) and provide you with an estimate for repair.

skipcfd

Ok, yea the only thing I can think is when I removed my seat to remove the carpet, the light came on. "I think" But, they said, that I have to agree to a diagnostic test fee, but it would be more than likely covered by Honda because it's a Safety concern. They also did a inspection, and told me that the care had no issues. Well first, the ac hasn't worked in 2 years, and there was no overfill cap on the recovery tank. I am calling them out on it today and see if they really did actually look at the vehicle.

Colin42

Did you disconnect the battery and wait for a bit before removing the seat?
If you didn't that would've pissed off the computer and turned on the air bag light.
I did that in my old car

ezone

This is normal just about anywhere.
However, if the issue was caused by their work that diag fee should be cheerfully refunded.

No, it doesn't always work this way.
I assume you received a copy of their inspection checklist. Does the checklist specifically state the tech is to check the operation of the AC system?

The checklist is strictly visual, no tools involved, no diagnosis, nothing more than observations.
Of course LOL.

The inspection is only as thorough as the person doing the inspection.
Some may see it as an opportunity to bring legitimate service needs to your attention, others may see it as an opportunity to write a shopping list of gravy services that generate revenue.
Some don't even do that much, some may simply check a bunch of boxes without ever seeing the car.

A free inspection is sometimes worth exactly what you paid for it.

skipcfd

Well, we have checked everything. We even hooked the sensor to the battery to see if it would heat up, and nothing. There is power to the connector as well. It would be odd that I would have two bad brand new sensors. Any other thoughts?

ezone

Sensor heater circuit measured ____ ohms resistance??

Which wires did you use to check this ?