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90 CRX
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Discussion Starter #1
So yes i've googled the ish outta this and still cant come across a straight answer

So i had the code 41 for bad heater circuit, but it was constant. So as soon as i'd start the car, pop, code 41

Now, with the new (denso) sensor, after driving on the highway for about 10 mins the code pops back up...

Any advice would be greatly appreciated before i just set this damn car on fire
 

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Did you replace the O2 sensor with an OEM style plug or a universal pigtail? In either case, compare the ECU pinout to the pinout for the O2 sensor. Don't go off of random forum posts for the O2 sensor pinout as every O2 sensor can be slightly different. Preferably, get the data sheet for your O2 sensor from the manufacture's website if available or another reputable source.
 

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Sloppy Jalopy
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check the resistance of the 02 heater on the old one and the new one .

,maybe a bad wire... so also check for batt voltage on 02heater circuit.
 

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90 CRX
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Discussion Starter #4
Did you replace the O2 sensor with an OEM style plug or a universal pigtail? In either case, compare the ECU pinout to the pinout for the O2 sensor. Don't go off of random forum posts for the O2 sensor pinout as every O2 sensor can be slightly different. Preferably, get the data sheet for your O2 sensor from the manufacture's website if available or another reputable source.
check the resistance of the 02 heater on the old one and the new one .

,maybe a bad wire... so also check for batt voltage on 02heater circuit.
pretty sure my wiring is all good... besides if it was a wiring issue wouldnt the CEL come on immediately, not only after driving for a period of time
 

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Love the Civic
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ECU issue?
 

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How did you reset the ecu?

It could be the wiring. There could be a brake or connection problem that when driving moves and loses the connection setting off the cel.
 

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besides if it was a wiring issue wouldnt the CEL come on immediately
Not always. I've had this issue before. I was using a universal O2 sensor and a P28 ECU with an OBD0 harness. The O2 code wouldn't come on until I started the engine, which lead me to believe I had my signal wire mixed up with another wire, possibly a ground. Eventually I got the wiring sorted and the problem went away.
 

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94 Integra
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The heater wires can be mixed (it's just a glorified resistor), but the two signal wires can't be swapped. Here's a quick list for colors: http://www.aa1car.com/library/o2_wire_chart.jpg Match your sensor's wire colors to one of the brands, then match to your OEM wire colors.

The other thing that can happen is your wiring in the harness could be shot. If the wire that comes from the ecu or to ground is cut/broken/shorted, it doesn't matter what O2 you plug replace it with. It could also be the ecu, but that's less likely. When the wiring is 20+ yrs old and/or modified, it's usually the culprit. Many people solder instead of crimp, and many of those people have very poor soldering & flux-cleaning skills.
 

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90 CRX
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Discussion Starter #10
How did you reset the ecu?

It could be the wiring. There could be a brake or connection problem that when driving moves and loses the connection setting off the cel.
Resetting the ecu by disconnecting the battery for like 5 mins

Not always. I've had this issue before. I was using a universal O2 sensor and a P28 ECU with an OBD0 harness. The O2 code wouldn't come on until I started the engine, which lead me to believe I had my signal wire mixed up with another wire, possibly a ground. Eventually I got the wiring sorted and the problem went away.
I'm using a denso sensor, so pretty much OE replacement... and the CEL ONLY comes on after highway driving

The heater wires can be mixed (it's just a glorified resistor), but the two signal wires can't be swapped. Here's a quick list for colors: http://www.aa1car.com/library/o2_wire_chart.jpg Match your sensor's wire colors to one of the brands, then match to your OEM wire colors.

The other thing that can happen is your wiring in the harness could be shot. If the wire that comes from the ecu or to ground is cut/broken/shorted, it doesn't matter what O2 you plug replace it with. It could also be the ecu, but that's less likely. When the wiring is 20+ yrs old and/or modified, it's usually the culprit. Many people solder instead of crimp, and many of those people have very poor soldering & flux-cleaning skills.
i will try switiching my blue and white wires and see what happens... my harness colors are blackx2 white and green, so i naturally assumed that green would match to blue since the other three colors match up, but after looking at that link you provided i may have been mistaken, but i still feel like if that is the problem my CEL would come on as soon as i start the car... not after driving for a while on the highway.
 

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Try pulling the back up fuse to reset the ecu. Sometimes just pulling the batt cable won't reset the ecu.
 

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98 Civic HX D16Y5
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Try pulling the back up fuse to reset the ecu. Sometimes just pulling the batt cable won't reset the ecu.
Or disconnect the negative battery terminal and turn the key to the on position, wait a few mins, turn off and reconnect the battery.
 

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90 CRX
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Discussion Starter #17
Thank you all for the much needed assistance and spit-balling...

i have FINALLY solved the problem..

Some of you may know that this really started with me thinking i had a code 4, as opposed to 41, and all the tribulations i went thru with that before realizing it was in fact a 41...

Since then i purchased the new 02 sensor believing all my wiring was good..of which the continuity was one of the things i checked (and had) leading me to believe the wiring was fine..

Well it turns out that though the wiring had continuity... the wire for the signal ground was badly corroded and stiff at a joint in the looming.... so i cut that section out and re-crimped it with a new connector and viola! No more CEL

I'm guessing there must have been enough continuity to make my DMM beep for the test, but either after warming up it lost that continuity or maybe it was too weak for the ecu... either way this was definitely my problem as i have now driven two days with much highway driving and haven't seen the CEL.

So again, big thanks DSO!
 

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Classic Man
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A continuity test from a multi meter passes 1v through the wire, and no load what so ever.

A voltage drop test would have been much much more efficient. And you would have known your wiring was bad.
 

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90 CRX
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Discussion Starter #20
Yep, continuity is different from amp capacity. Just because a phone wire has continuity doesn't mean it can carry 100 amps. The heater is supposed to be ~1 amp or 12-14 watts. Was it originally a sealed crimp (covered in shrink tube), exposed crimp (plastic cover), or soldered?
soldered by whoever did the very first swap many moons ago... i replaced it with an exposed crimp i guess... the basic slide a wire in each end and crimp, no heat shrink tube
 
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