O2 sensors are driving me nuts!
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Northstar Engines and System Technical Discussion Discussion, O2 sensors are driving me nuts! in Cadillac Engine Technical Discussion; I havent had an insufficient activity code in at least 2 days. But i have changed the front sensor 3 ...
  1. #1
    ponyboyt is offline Cadillac Owners Enthusiast
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    O2 sensors are driving me nuts!

    I havent had an insufficient activity code in at least 2 days. But i have changed the front sensor 3 times with 3 other known good O2 sensors. I did the third one yesterday at lunch, and put about 250km on the car between that and going to bed. Not one code, mileage still seemed a bit off, throttle response was a bit off but i saw a gain in power at high RPM.

    This morning i start the car cold and immediatly check for codes..

    P0135 and P0155. Front sensor, and rear sensor, "Heater performance". It's sluggish and boggy with anything other than very light throttle. Once it warms up its fine, but still not perfect.

    Symptoms... Warm, off the line, it pulls hard. "Traction engaged" comes quick after 2 or 3 chirps (i have good tires) and about half way up the RPM's it starts pulling hard. Shifts hard into 2nd with a nice "squawk" but when the RPM's drop it feels weak and squishy.. then all of a sudden about a second after the shift its like it pulls again, almost feels like its shifting into second twice, there is a second "jerk" and then starts pulling again.

    I cleaned the carbon off my bumper, couldnt get much out of my tips. Trying to see if it comes back and how fast.

    I checked the voltage when i changed the sensor yesterday with the key on, at the O2 fuse, 10.5 volts. At the plug, 10.5 volts. Should i check them cold? Actualy, when i checked it at the fuse the needle on my meter went all the way to the right, almost pinned.... but at the plug it stopped at 10.5

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    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: O2 sensors are driving me nuts!

    Are you using A/C Delco sensors?

  4. #3
    ponyboyt is offline Cadillac Owners Enthusiast
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    Re: O2 sensors are driving me nuts!

    yes. Some back history... this is the engine i swapped. Didnt have O2 sensor problems before the swap, now 3 are ""bad"". I think something else is up... so instead of buying 3 sensors .. i took 3 from another car that i know work (98 deville). And got another from a 97 sts. I've tried all 3 of those sensors, they are all OEM.

    Is there a way to test the heaters? If thats even the problem... i dont think its really all that possible that the stars are alligned and i have 6 bad sensors here... just doesnt seem possible. It is VERY intermittent, but the codes have remained current all day, oddly though, the code for my post cat has not returned yet....

  5. #4
    Submariner409's Avatar
    Submariner409 is offline If it won't run, chrome it
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    Re: O2 sensors are driving me nuts!

    Trace and find the harness grounds and connectors for the O2 sensors. Clean everything. ALL 4 sensors use calibrated wiring and the ground circuit for an input called a "clean air reference". ANY electrical problems in the circuit, even replaced or spliced wiring, and they'll never work correctly.

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    Ranger's Avatar
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    Re: O2 sensors are driving me nuts!

    DO NOT clean the sensors themselves though.

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    ponyboyt is offline Cadillac Owners Enthusiast
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    Re: O2 sensors are driving me nuts!

    do all 4 wires on each sensor go through loomed cables with the rest of the wires? That could be fun.... Im back to needing someone with a scanner. Looks like the easiest one to check first is the post-cat.

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    codewize's Avatar
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    Re: O2 sensors are driving me nuts!

    It's such a rare thing to have an O2 sensor go bad. 99.999% of the time if you're seeing a code for an O2 sensor, something else is causing it. Either causing false readings or causing the sensors to get fouled up.

    On my 93 Brougham I had the same type of thing going on. After 2 years or so and $100's in diag and repair bills I finally figured out it was a bad cat, that everyone told me wasn't the problem.

    After replacing the cat the car ran like new and never threw another code.
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    zonie77 is offline Cadillac Owners Connoisseur
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    Re: O2 sensors are driving me nuts!

    Quote Originally Posted by codewize View Post
    It's such a rare thing to have an O2 sensor go bad. 99.999% of the time if you're seeing a code for an O2 sensor, something else is causing it. Either causing false readings or causing the sensors to get fouled up.

    On my 93 Brougham I had the same type of thing going on. After 2 years or so and $100's in diag and repair bills I finally figured out it was a bad cat, that everyone told me wasn't the problem.

    After replacing the cat the car ran like new and never threw another code.
    I totally agree, vacuum leaks, leaky injector, bad cat, all can cause the O2 sensor to throw a code and yet the 02 sensor is good.

  10. #9
    ewill3rd is offline Cadillac Technician
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    Re: O2 sensors are driving me nuts!

    First of all, it isn't helping to refer to the sensors as "front" and "rear".
    Sure that is where they are located but you should get into practice of referring to them as "bank 1" and "bank 2".
    That will avoid some confusion since on a N* has bank 1 on the rear and bank 2 on the front.

    Next, stop replacing sensors. Those codes are for HEATER PERFORMANCE, not sensor performance.
    Heater performance codes are related to the heater circuit and CAN be a bad sensor but I'd say you have pretty much ruled that out. The only concern I have is that you keep saying "known good" rather than "new". We'll put that aside for now.

    Step 1 is to go to the fuse block and check the O2 sensor heater fuses.
    I am still foggy as to which car you are working on.
    You have 2 listed under your name and although they are probably not much different, they could be.
    If you are measuring from the heater voltage circuit to ground with the key on, no, 10 volts is not good.
    The pink wire should have battery voltage on it with the key on or in the crank position.
    Now if the battery voltage is 10 volts and you have 10 volts at the sensors on the pink wire then okay, fix the battery...
    Don't use a multimeter, find a test light.
    A multimeter will show voltage even if the circuit is crap, if it is not a "working" circuit.
    If you ground a test light then touch it to the heater circuit it should light, if it doesn't you could have a bad connection, faulty splice or wiring issue that needs to be addressed. Remember resistance in a circuit is voltage drop, voltage drop in a circuit will kill a load faster than you can say Tesla.

    I do replace a few O2 sensors but not for heater codes, usually for actual sensor performance codes.

    If the fuses are blown you need to check the harnesses to be sure they are not shorting out somewhere and fix that or you will keep at this.

  11. #10
    ponyboyt is offline Cadillac Owners Enthusiast
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    Re: O2 sensors are driving me nuts!

    Thanks ewill3rd! Yes, this is my 97 (sts). I assumed that for now i should not waste money on 3 new sensors because they probably are not bad, they were working just fine before we swapped this engine. I suspect the PCM or wiring harness. I had a test light ready to go when i popped the hood and it is burnt out :P The sensors i have on my bench are from 2 other cars that had no problems. I figure hey, the bank 2 sensor is easy enough to change, ill try at least 3 of those before i start spending money on new ones. Fuses are fine btw, ive checked and cleaned them.

    The thing is, i will NOT get a heater performance code all day if the car stays warm. This is why i originaly decided against buying new. It would be throwing money away. I dont mind throwing time away, as its experience Early morning cold starts will throw these codes. And its always the same... like day one, the first 2 will throw a code (manifold sensors) then the next day the post cat. the pre-cat has never thrown a code, which is also throwing me off cause im thinking if its a bad circuit somewhere..... well i will have at it this afternoon with a new test light and see what we find.

  12. #11
    tateos's Avatar
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    Re: O2 sensors are driving me nuts!

    Quote Originally Posted by ewill3rd View Post
    First of all, it isn't helping to refer to the sensors as "front" and "rear".
    Sure that is where they are located but you should get into practice of referring to them as "bank 1" and "bank 2".
    That will avoid some confusion since on a N* has bank 1 on the rear and bank 2 on the front.

    Next, stop replacing sensors. Those codes are for HEATER PERFORMANCE, not sensor performance.
    Heater performance codes are related to the heater circuit and CAN be a bad sensor but I'd say you have pretty much ruled that out. The only concern I have is that you keep saying "known good" rather than "new". We'll put that aside for now.

    Step 1 is to go to the fuse block and check the O2 sensor heater fuses.
    I am still foggy as to which car you are working on.
    You have 2 listed under your name and although they are probably not much different, they could be.
    If you are measuring from the heater voltage circuit to ground with the key on, no, 10 volts is not good.
    The pink wire should have battery voltage on it with the key on or in the crank position.
    Now if the battery voltage is 10 volts and you have 10 volts at the sensors on the pink wire then okay, fix the battery...
    Don't use a multimeter, find a test light.
    A multimeter will show voltage even if the circuit is crap, if it is not a "working" circuit.
    If you ground a test light then touch it to the heater circuit it should light, if it doesn't you could have a bad connection, faulty splice or wiring issue that needs to be addressed. Remember resistance in a circuit is voltage drop, voltage drop in a circuit will kill a load faster than you can say Tesla.

    I do replace a few O2 sensors but not for heater codes, usually for actual sensor performance codes.

    If the fuses are blown you need to check the harnesses to be sure they are not shorting out somewhere and fix that or you will keep at this.
    Lot's of good info

  13. #12
    ewill3rd is offline Cadillac Technician
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    Re: O2 sensors are driving me nuts!

    pony, it won't throw heater perf codes on warm start ups because it can't.
    The enable criteria for heater perf codes usually require a fairly cold start up temp. The computer has to have a baseline to start from to monitor the speed of closed loop operation.

    Remember the heaters are to help get the sensors to operating temperature quickly to limit open loop operation. I can explain that in more detail if you guys want.
    If the car is warmed up, the computer can't gage how long it takes for them to go active so it doesn't bother.
    Get your test light fixed.
    From year to year it varies how they operate. I only had access to the 98 manual when I looked up the codes but as I said the 97 shouldn't be much different.
    There are switched fuses that send B+ to the sensors and they are grounded somewhere else or even back to the PCM.
    Later vehicles used power feeds and even sometimes grounds from the PCM and some of them even only command the heaters on at certain times rather than older systems where they are switched on all the time the key is on.
    I usually use a small test light I built years ago that I can stick in the O2 connector engine harness side. I go from the heater ground to the heater power feed and then turn on the key, if the light lights up then I know my heater circuit is good.
    I'd have to do some schematic digging to know exactly how those are wired up if you need advice on where to look.

    Good luck, keep posting and I'll help when I can.

  14. #13
    ponyboyt is offline Cadillac Owners Enthusiast
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    Re: O2 sensors are driving me nuts!

    Quote Originally Posted by ewill3rd View Post
    pony, it won't throw heater perf codes on warm start ups because it can't.
    The enable criteria for heater perf codes usually require a fairly cold start up temp.
    4 degrees C outside today. This mornings codes:

    P0135 current DTC P0135 HO2S Heater Performance Bank 1 Sensor 1
    P0155 current DTC P0155 HO2S Heater Performance Bank 2 Sensor 1

    did not clear codes.

    an hour after i get to work, i start it up again. Temp needle goes to the 1/4 mark right away. Check codes:

    P0135 current
    P0155 current

    did not clear codes.

    service manual: Bank 1 sensor 1 is rear sensor (right side manifold, between engine and firewall?) Bank 2 sensor 1 is front sensor (left side engine manifold).

    The way i read your quote, since the car is warm (at the 1/4 mark) when i start it, these codes should for no reason be appearing?

    On a side note: Lets say (because its a possibility) that my PCM is fried. A mistake was made hooking everything up when we did the engine, one that ive seen on this forum before. The POWER cable for the fuse block was grounded to the engine block, and power was put to the battery via a charger. I immediatly removed the cables when i saw it smoking at the battery, and looked for the problem and found it pretty quick. Another wiring mishap was that both the grounds from the battery were bolted to the engine. I spotted this one the next day, and corrected the 2nd ground by replacing it to the body. During the time it was grounded to the block the car would barely turn over, i had the PCM laying in its box but off to the side for accessibility. I also noticed that it was smoking when trying to turn over the car. I thought then that it was fried but the next day the car ran so i figured it was ok.

    I have the PCM from my 98 deville. If i have it flashed to my 97 STS by the dealer it should work? Just need to program the key? This will be a step i take this weekend if i can't figure out whats up with the sensor wiring. Im also looking at a new(used) harness off another 97 STS in case any of my wires got melted from that bad ground. Just possibilities.

  15. #14
    ponyboyt is offline Cadillac Owners Enthusiast
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    Re: O2 sensors are driving me nuts!

    waited 4 days to be sure....

    THROTTLE

    POSITION

    SENSOR

  16. #15
    ponyboyt is offline Cadillac Owners Enthusiast
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    Re: O2 sensors are driving me nuts!

    well that lasted all of 5 or 6 days.... cold start one morning and all those codes are back.

    Well yesterday i spent most of the day digging and digging, through here and google. I found some old threads with lots of posts from evilward and codewise; thanks guys

    After reading some very detailed descriptions, i popped the hood and pulled the breather, had a good look around under the coolant hoses and finaly found what i was looking for. About 3 inches of small guage wire coming out of the loom, the end of that black wire had its eyelet broken off and was just dangling there. This is the ground wire for the O2 sensor heaters. Very common break, apparently can happen as the eyelet breaks when you try to remove the nut from the stud it should be bolted to. So much stress on wrists, forearms and shoulders, much patience and a set of flashlight batteries, i finaly clipped the broken eyelet off, trimmed the wire, and put a new eye on and re-attached it to a new stud.

    Cold start this morning, as of yet, NO codes.

    Im still running like crap. Lots of power loss at anything other than "normal driving RPM range". Im waiting for an insufficient activity code to pop up again, then more toubleshooting

    Good news is, i got an offer for this car, and i kept no secrets. If i let her go, i can move on to my 99

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