Hello everyone,

Short and to the point: My 1997 Honda Civic DX 2DR Manual has the Check Engine Light on for both the primary and secondary oxygen sensors. Any help? both the DTC 41 and DTC 65 codes.

More details: My civic has both the DTC 41 and DTC 65 codes. These are DTC 41 - P0135 Front HO2S Heater Circuit Fault (Sensor 1) and DTC 65 - P0141 Secondary HO2S Heater Circuit Fault (Sensor 2). My friend replaced the secondary oxygen sensor with a new, but likely aftermarket, O2 sensor. Both signals were still being sent. I went to a mechanic shop and the mechanic plugged in a new primary oxygen sensor, and yet again both codes still appeared. He requested I return on weekdays but I fear mechanical repairs fees. I find it unlikely that it's the actual O2 sensors. I checked the fuses, particularly #15, and they seem fine. I took fuse 15 and switched it with the fuse that controls the turn signal of the car. The turn signal worked, so that means the original fuse #15 worked (both are 7.5 A). The exhaust system (all the way from the exhaust manifold to the muffler) are aftermarket. I'm honestly not sure if there is a catalytic converter, but regardless, if there wasn't a catalytic converter, the Primary oxygen sensor signals should not have been sent, but rather only the secondary oxygen sensor. I don't know if this is relevant to the codes or the condition of my car, but at the moment my heater doesn't seem to be working either.

Thank you very much for your time and for your input. I really appreciate it!

 

If the fuses are good test the heater wires on both sensors
http://troubleshootmyvehicle.com/hon...sor_test_1.php

If they test good check the wiring going to the sensor for any open or damaged wiring.

 

7.5 A fuse 15 does not protect the turn signal circuit in a 97 Civic.

Voltage test fuse 15 as described in the Test Fuses link in my signature.

 

Thank you for the responses guys. I'll keep you updated.

 

To HondaPartsHero: I checked out the sensors, although I don't think it's that. However, I believe you're onto something. I think one of the previous owners messed around with the wiring. I'll definitely check out the wiring, especially on the engine harness side of the O2 sensor. I just have to figure out which wires are the right ones for a 1997 honda civic since your post regards an accord.

To RonJ@HT: what I did was remove the fuse in fuse socket #15 and inserted it into fuse socket #12 (which controls turn signals) to see if the fuse would work. My turn signals did indeed work, so I assume fuse #15 works fine. I will check it again however with your more advanced method.

 

 

i think Ron nailed it on this one, this one particular problem can be a doozey, good advice here

 

Thanks HondaPartsHero!

 

EDITED
Here's my update:
I checked every fuse under the dashboard and they all passed the continuity test - no blown fuses. So did the fuses under the hood.
I then tested each fuse by grounding the negative black lead and connecting the positive red lead of the multimeter to each probe of every fuse, except those I didn't have attached under the dashboard (1,2,6, and 29).
Fuse 1, 2, 6, and 29 are, according to the fuse diagram, are "Not Used"

-When the ignition was ON with the engine off, fuses 4, 5, 20, 21, 22, 30, 31, and 32 displayed 0 Voltage. (The description of these fuses are shown further below)

-When the ignition was ON with the engine off and the low beams on, fuses 4, 5, 20, 21, 22, and 31 displayed 0 Voltage, but fuses 30 and 32 now displayed typical voltage (around 12 V).

-When the ignition was ON with the engine off and the high beams on, fuses 20, and 31 displayed 0 Voltage. Oddly, fuses 4 and 5 increased from 0 Voltage to 0.6 Voltage. I don't know if this indicate something.

Fuse 4 - "Right headlight (high beam)"
Fuse 5 - "Left headlight (high beam), high beam indicator light"
Fuse 20 - "Daytime running lights relay (Canada)"
Fuse 21 - "Right headlight (low beam)"
Fuse 22 - "Left headlight (low beam)"
Fuse 30 - "Dash lights, option (dash lights)"
Fuse 31 - "ECM/PCM, PGM-FI main relay, integrated control unit"
Fuse 32 - "Front parking lights, taillights, license plate lights"

Interestingly, fuse 4 and 5 control high beams - I have high beams (aftermarket, however. The previous owner installed that). Fuse 21 and 22 are low beams - I have low beams. Fuse 30 controls dash lights - I have dash lights. Fuse 32 controls parking lights, taillight, and license plate lights - I have this. Fuse 20 is daytime running light's for Canada, so I believe it makes sense that there is 0 Voltage.

The main question here is: Why do these fuses display 0 voltage, but their components still work. Also, I find it hard to believe that the ECM/PCM isn't receiving voltage. Wouldn't that affect many other things, and cause the car to send even more CEL/MIL codes?

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I then followed the steps recommended above in the manual.
1. I checked the upstream O2 sensor by following the initial steps. DTC P0135 and P0141 are indicated.

2. There are between 10-40 Ohms (to be precise, 16) between terminal 3 and 4 of the O2 sensor connector.

3. With the red led securely taped down onto a good ground, I used the black probe to test the terminals. I tested both oxygen sensors: On one of the sensors, terminal 1 (top left) showed -1 ohms, and terminal 4 (bottom right) showed -645 ohms. For the other sensor, terminal 1 (top left) showed 990 ohms, while terminal 4 showed -645 ohms. There wasn't any continuity b/w terminal 2 and ground, and terminal 3 and ground on the engine harness side of either of the two sensors.
The test wanted to know if there was continuity. Although there was, they were in terminals 1 and 4, rather than 3 and 4, and they were also bad (except for the -1). Therefore, rather than going to the step of replacing the O2 sensor, I continued on below.

4. When connecting terminal 3 and 4 of the engine harness side of the O2 sensor connector, voltage was displayed.

5. Finally, I checked for continuity from terminal C1 of the ECU wire harness side, the female side. There was no continuity between C1 and ground.

It recommends to replace the ECU with a known working one to see if symptoms go away. Since I don't have access to that, my next step would be to buy one, unless anyone else has ideas. I'll update