355 - 1995 O2 sensor replacement DIY? | FerrariChat

355 1995 O2 sensor replacement DIY?

Discussion in '348/355' started by RudyP, Jul 1, 2019.

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  1. RudyP

    RudyP Formula Junior
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    I just got a Check Engine 5-8 light on my new to me 95 Berlinetta. Checking the codes revealed 1211 and 1212 so I ordered a new Bosch O2 sensor to see if that fixes it. Is there a good DIY on how to replace the sensor? I can see where the sensor is plugged into the cat but not where the wire connector goes to or the wire routing in general. I’m trying to decide if this is something I can tackle myself or will require professional service.

    I found the diagram below but it does not show where the connector plugs in.
    [​IMG]
     
  2. MAD828

    MAD828 F1 Rookie
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    Oct 8, 2011
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    Elliott Caras
    Its an easy DIY, the o2 sensor wire routing is even easier on a 95 as they don't have fore and aft sensors. In the diagram you posted the sensor wire is mounted on a tab marked location 76.
     
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  3. yelcab

    yelcab F1 World Champ
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    Nov 29, 2001
    12,661
    San Carlos, CA
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    Mitchell Le
    Very easy job with a 22 mm wrench to remove the O2 sensor. Its connector is found at the left hand side of the engine bay, under the black side cover. The connector housing is attached to the subframe via a tab that requires a 7mm socket to loosen.
     
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  4. Qavion

    Qavion F1 World Champ
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    Feb 20, 2015
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    Ian Riddell
    Some folks add a little nickel paste to the O2 sensor threads prior to installation to make it easier to remove next time. The old sensor may be hard to unscrew. A heated exhaust may help, but then you run the risk of burning yourself.

    The plugs will be in a similar location to the ones in this photo (bottom middle) near the orange-red suspension strut actuator. That's a 5.2 car (with the side cover removed), so there are two plugs in the photo.

    Image Unavailable, Please Login

    You may have to clear the codes, do a battery reset and let the car idle for 5 minutes (aircon off) to allow the engine ECU to get used to the new sensor.
     
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  5. RudyP

    RudyP Formula Junior
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    It looks like this is where the connector is on my car. Does that seem correct? It is not attached to the subframe via a tab like item 76 in the diagram at the top of this thread...
    Image Unavailable, Please Login
     
  6. drbob101

    drbob101 F1 Rookie
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    Nov 26, 2012
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    Tinton Falls, NJ
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    Bob Ferraris
    Easy as long as prior tech put anti seize on them. My first experience was with one that didn’t have it. Fortunately I was replacing the cats because even on the bench with leverage and soaking it wouldn’t come out.
     
  7. Qavion

    Qavion F1 World Champ
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    Feb 20, 2015
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    +1

    Yes, that's the plug. I could give you the colours of the wires from the wiring manual, but it looks like your wire colours are beyond recognition. After reinstallation, make sure the harness is not resting on the cat or other hot components.

    Take note of the car's Assembly No. plate seen in the top right hand corner of your photograph. It will help you identify spare part numbers in the future.

    That larger plug bolted to the car above the O2 plug is a multi-purpose plug and some essential wiring running through it:
    Starter motor solenoid power
    Signal from speedo sensor on the gearbox
    Oil Pressure Transmitter signal
    Engine coolant (water) temperature information
    Aircon compressor clutch engage signal
    Alternator control and warning light wiring
     
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  8. krazykarguy

    krazykarguy Formula Junior

    Apr 17, 2014
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    Fort Mill, SC
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    Matt
    One other point I'll mention is to disconnect the sensor connector and any tie downs before trying to remove them from the converters. You do not want to be twisting the wiring on the new sensors because you put together the connector first and then screwed in the sensor. That's a good way to break/stress wiring.
     
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  9. RudyP

    RudyP Formula Junior
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    Thanks for everyone's help on this. I replaced the O2 sensor with a new one, cleared codes and reset the ECU and started up with no check engine light. I let it idle with all accessories on for 15 min...and the check engine 5-8 light came back on (darn!). Went for a 10 min easy drive and the light would come and go. It was mostly off but would come back for a few seconds at a time, seemingly when idling or at lower engine rpm.

    Prior to this change, the light was permanently on and now it is mostly off but sometimes comes on. So it seems changing out the sensor helped some but did not fully solve the issue. I'm going to go for another, slightly more energetic drive in a few minutes to see how it goes.

    Any other ideas?

    Rudy
     
  10. brendon0

    brendon0 Formula Junior

    Dec 13, 2003
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    swap the mafs side to side quick easy job
    and see if the code moves to the other bank.
     
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  11. RudyP

    RudyP Formula Junior
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    Thanks brendon0 - i took your (and others' including yelcab's) advice and swapped the MAFs side to side. I just came back from a 20 min test drive and... no CEL at all. It didn't move over to the other bank, it just went away altogether.

    I'll give it a few more drives before declaring the issue 'fixed' but it is encouraging. Since there is no right bank fault, I'm wondering if the connector had jiggled itself loose a bit and there was maybe a bit of an intermittent connection or something.. Or maybe just some on-the-margin incompatibility between the MAF and other aspects of the left side ECU system that randomly happens to fall within spec when moved over to the right side - not sure if that makes sense... I did not touch the or do anything to the MAFs other than swapping them left to right.
     
  12. johnk...

    johnk... F1 World Champ
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    Jun 11, 2004
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    When I first read this thread I thought MAFs or vacuum leak. CEL may come back. Clean the MAF contacts and connectors and clean the MAF. You can get MAF cleaner at any auto store.
     
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  13. brendon0

    brendon0 Formula Junior

    Dec 13, 2003
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    keep driving, the code will come back.

    Do an ecu reset too. Battery off, ac and
    accessories off, crank and idle 10 minutes
    then drive it like you stole it. Yes 10 minutes
    not 5 as advised above.

    I chased the 1212 and 1212 ghosts for 10 years. Finally solved with new o2 sensors
    and rebuilt mafs.

    Let us know when it returns, I can point
    you in the right direction for maf rebuilds
     
  14. RudyP

    RudyP Formula Junior
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    Well you guys aren't encouraging...

    You may well be right but at least it is gone now and if rebuilding MAFs and relatively inexpensive O2 sensors are the solution that can be managed.

    Brendon - regarding your suggestion to reset ECU. I did that before I swapped the MAFs but after putting in the new O2 sensor. Do you recommend another reset now? What is the purpose since I no longer have CEL on (at least for now)?

    Thanks again for your help!
    Rudy
     
  15. brendon0

    brendon0 Formula Junior

    Dec 13, 2003
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    Brendon
    The MAF sends a voltage signal to the ECU based on the mass airflow it is reading. The ECU "adapts" to this signal and stores it in memory.

    This is why the code comes back and goes off, if the MAF is intermittent then we get check engines.

    If the idle learn establishes a range off the bad MAF and then gets a signal from the good MAF on restart your codes wont be accurate.

    Just do the relearn after the swap, its 10 minutes...

    FYI I used "Fuel Injection Corp:" out of California. Its the first link that comes up. They did a stellar job. Both mine bench tested fine, but
    the owner noted that these are finicky.I just had them both rebuilt and new O2 sensors put in (did it myself). Problem has been gone for a year. O2's came from Ricambi, in this case I went with OEM parts because I was tired of chasing ghosts.

     
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  16. RudyP

    RudyP Formula Junior
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    Thanks for the reference and the explanation which makes sense.

    I'm not at all dead set against resetting the ECU but given that I have no CEL on currently, what would be gained at this stage? It seems like that could go one of two ways - a) the reset with the new MAF position voltages stays within spec and the light stays off or b) the reset establishes a new parameter range that the now right side MAF sometimes falls out of range and I get intermittent CELs. In path a) it seems I am no better off and in path b) I am worse off having triggered the CEL.

    Am I missing something? Will the un-rebuilt MAFs drift enough over time that CELs are inevitable and you are arguing I might as well diagnose it earlier and send in the for rebuild sooner? Is this currently fortuitous misalignment of ECU range against MAFs that is preventing the CEL coming on actually masking a real issue that is potentially causing damage? That seems unlikely given the tightness off the ranges and the general feeling that these CELs are almost universally sensor issues rather than legitimate engine issues that can result in mechanical failure. But perhaps I'm wrong on that last point.

    Thanks for continuing to weigh in - I appreciate the input!
     
  17. brendon0

    brendon0 Formula Junior

    Dec 13, 2003
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    Brendon
    You are trying to identify a failed part sooner than later. It may be fine today, but 4 months from now when it comes back on, your going to have forgotten which
    side you swapped to which and which CEL light came on before. Also the range might move on the ECU for the working MAF and the computer may retard the
    spark alittle because it expecting different value ranges.
     

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