waaBAAH

i work at a shop, vehicle comes in with C.E.L. on.

3 codes listed are p0301, p0302, and p0420. cyl 1 misfire, cyl 2 misfire, cat below threshold. (184,000) 97 HX runs fun and no misfires felt on test drive. no exhaust leaks found from the smoke test to condem cat. i also swapped the spark plugs around to see any changes in misfires. i cleared all the codes and let the monitors reset to see if anything has changed, and no codes came back on at this time.

my question is this, i was looking at the o2 readings and while cruising at 60+ second o2 was basically flatlined at around .0v-.1v front o2 was flatlined at .45v. some more research revealed that this d16y5 motor is vtec-e and a lean burning motor with a 5 wire wideband o2. my boss first stated that we have to replace the front o2 sensor in order to properly diag. this car. i told him that the 5 wire o2 is a wideband and that the flatline condition (giving the car gas the front o2 would switch) is normal. he would like a test doen to see if the o2 is working as intended but i came up short on tests. alldata and mitchell are not explaining the 5 wire function of this step-child motor.

is the flatline reading of the o2 normal? what is the testing procedure of this 5-wire o2? i would hate to tell the customer you have to replace this 400 dollar o2 and then have his C.E.L. back on for the problmes that i didnt look into with misfire and cat.

Thanks ahead to you guys

Former User

Besides the CEL codes that have not returned yet, is the engine having any running or low mileage issues?

waaBAAH

all i really know is that the customer wanted to pass emissions by us and that we couldnt due to C.E.L being on. customer hasnt said anything of driveability problems or low gas milage. i did drive the car for about 30 miles on the highway uphill and downhill with loading the motor when i was going uphill high and low rpms.

there might have been a "bogging" issue going up one hill (out of the 30 ish hills). felt underpowered where rpms were dropping in fifth gear @ 60ish even while i started to slowly floor the pedal. i downshifted and vehicle then resumed normally. i should have looked at the scanner but naturally i just downshifted to pick up speed

Former User

For the primary O2 sensor, I would think that an average voltage of 0.45V would be right where you want it. What type of scanner are you using? Is it able to detect the rapid voltage waveforms?

I was more struck by the low voltage reading by the secondary O2 sensor. I would think it should be more similar to that of the primary O2 sensor.

Also, regarding the misfires, have you checked the plug wires, cap, and rotor? If such misfire was severe enough, the cat might have been damaged.

waaBAAH

yes...plugs were inspected and they were ever so slighlty rounded at electrodes. my guess would be 20k-30k. white porclein was slighty rusted at the bottom base were the hex head is. ngk r Plug ends are more whitish but a little research resulted in me finding out this motor is a more leaner running motor then the other d series. so i am guessing that whiter is better then tan in this case only.

the cap and rotor looked ok...little whitish ends and 3 and 4 cap ends looked slighlty out of line (bent). nothing i would condem right away. fuel test not really done...but all the injectors were pulsing and opening time on injectors was around 2.5msec



scanner i am using is a genesis. short term fuel trims are +.3 plus or minus 2.0. long term fuel trims are -.8. I wouldnt say the scanner is the fastest at changing maybe a 2 second delay refreshing every second i would assume. ive tested plenty of cars where you would see the "step" pattern from the o2's switching. this civic is not the case. no functions in scanner to see current misfire. i also couldnt find any freeze frame data to see how long the light has been on or what conditions set these codes. car is in alaska and tempatures easilly reach -40 so "false" codes are not that uncommon especially when they drive all winter with the light on then you check them when its 50 degrees outside.

the low readings on the second o2 was kind of weird. alldata test said in order to condem the cat i would need to drive the vehicle and see if the 2 o2 sensors were the same. (the same readings indicates the cat is not doing its job according to alldata) the low o2 readings indicate the cat is either storing the oxygen or an exhaust leak before the cat. i smoked out the exhaust and found no leaks. cat is part of the exhaust manifold so i am guessing that this piece is $500+ easilly.

its just this front o2 staying flatlined at .45v which is really getting me confused. we basically cleared the codes and told the customer to drive it around till monday so that we can do some research on this topic and to see which hard codes might come back on.

waaBAAH

this is basically where i stopped on the diag. i wanted and was ready to do a tune-up and a new cat but the front o2 not switching while cruising or idle (switches on accel) might explain the little bit leaner plugs/misfire and a bad cat reading. But i know nothing about the 5-wire wideband setups. To me it makes sense of the widebands to take smaller to no voltage increase/decrease (flatlines) readings taken by the o2 but for my boss it is completly far fetched that the voltage of this o2 doesnt move at idle or cruising.

both o2's have the ability to switch, (ive witnessed them max and min 0.0v-1.0v with throttle application) its just not switching cruising and or idle. Is this normal of the d16y5 vtec-e HX motor?

waaBAAH

TTT for all you honda techs that are slow at work. Woot!

waaBAAH

bump again.

Former User

I think this Wikipedia article may answer your question by saying that the non-fluctuating reading is normal for a wide-band O2 sensor:

waaBAAH

allright... thank you very much. i was searching the wrong areas then.

we will do a small tune-up plugs/cap/rotor and a cat. thank you for your help.

Former User

By the way, you seem to be a thoughtful mechanic. It's always good to know that they are out there.

I am no mechanic, but I wanted to throw in my 2 cents anyway. I thought the secondary O2 sensor reading was too low and should have been more similar to that of the primary sensor. With that said, I do not think P0420 is generally caused by a bad secondary O2 sensor.

So I would agree that concentrating on the misfire codes (intermittent?) is the best place to start. Is replacing the cat really called for if the P0420 code does not repeat?

waaBAAH

in this case..yes. reason being is the vehicle needs to pass emissions here in alaska. independent shops handle the emissions. since the vehicle failed with these codes it needs to be restested shortly after we fix the issue. if big brother was to do an audit on this car we could lose our license if we did nothing and just cleared the codes then retested. the misfire isnt that big of a concern for big brother sice computers do weird things in -40 below plus weather but the cat code is quite huge in the eyes of big brother eventhough it is also somewhat computer controlled.

basically car came in with 3 codes and not your typical one code. we have to at least throw on some part as bad as that sounds.

Former User

That's really unfortunate if the cat actually does not need to be replaced.