Emmissions Codes
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Northstar Engines and System Technical Discussion Discussion, Emmissions Codes in Cadillac Engine Technical Discussion; 96 STS northstar - I'd appreciate some comments on this. Almost every time I drive, at some stage in the ...
  1. #1
    thehammer is offline Cadillac Owners Member
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    Emmissions Codes

    96 STS northstar - I'd appreciate some comments on this.

    Almost every time I drive, at some stage in the journey I will get "Service Engine Soon - Emmissions Systems" come up on the display. Sometimes this triggers the "Service Engine" light, but not always. This almost always happens when I am idling at the lights - never while driving at speed.

    The service engine light usually goes off after 50-60 freeway miles.

    My mechanic said it might be dirty injectors. I have run around 6 bottles of Techron cleaner with various fillups, but not for a while, however the problem still keeps coming back!

    What is going on here. It doesn't seem to affect performance, but it sure is annoying!!

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  3. #2
    mcowden is offline Cadillac Owners Connoisseur
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    Re: Emmissions Codes

    Quote Originally Posted by thehammer
    96 STS northstar - I'd appreciate some comments on this.

    Almost every time I drive, at some stage in the journey I will get "Service Engine Soon - Emmissions Systems" come up on the display. Sometimes this triggers the "Service Engine" light, but not always. This almost always happens when I am idling at the lights - never while driving at speed.

    The service engine light usually goes off after 50-60 freeway miles.

    My mechanic said it might be dirty injectors. I have run around 6 bottles of Techron cleaner with various fillups, but not for a while, however the problem still keeps coming back!

    What is going on here. It doesn't seem to affect performance, but it sure is annoying!!
    Check the codes, look them up, and tell us what you find. We can tell you what's wrong and how to fix it. To learn how to check codes, read this thread:

    http://www.cadillacforums.com/forums...ad.php?t=53635
    Mike

  4. #3
    thehammer is offline Cadillac Owners Member
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    Re: Emmissions Codes

    OK, thanks Mike.

    Codes are as follows:

    PC0171 PC0174 PC0603 PC1520 IR1740

    No Codes for IPC, ACM, SDM, TCS, RSS, PZM, RFA, CCP

  5. #4
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Emmissions Codes

    Now go here for the code definitions.
    http://myweb.accessus.net/~090/dtcobd2.html

  6. #5
    thehammer is offline Cadillac Owners Member
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    Re: Emmissions Codes

    So I get the following:

    PC0171 and PC0174 are "Fuel Trim System Lean Bank 1 & 2"
    So I guess this means either the injectors ARE blocked up or else the car doesn't like running on 87 octane. I read a few of the threads about what fuel to run the N* on and see it is a well thrashed subject. I have noticed pinging once or twice when I have given it the all, accellerating from 0-50 as fast as possible, but that is the only time it happens.

    PC0603 - Control Module Long Term Memory Reset
    No idea what this means

    PC1520 - Transmission Range Switch Circuit
    I guess this is why I don't have OD - I don't know much about this.

    IR1740 - can't find this Code in the list...

  7. #6
    mcowden is offline Cadillac Owners Connoisseur
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    Re: Emmissions Codes

    Quote Originally Posted by thehammer
    So I get the following:

    PC0171 and PC0174 are "Fuel Trim System Lean Bank 1 & 2"
    So I guess this means either the injectors ARE blocked up or else the car doesn't like running on 87 octane. I read a few of the threads about what fuel to run the N* on and see it is a well thrashed subject. I have noticed pinging once or twice when I have given it the all, accellerating from 0-50 as fast as possible, but that is the only time it happens.

    PC0603 - Control Module Long Term Memory Reset
    No idea what this means

    PC1520 - Transmission Range Switch Circuit
    I guess this is why I don't have OD - I don't know much about this.

    IR1740 - can't find this Code in the list...
    The fuel trim system lean messages mean that the oxygen sensors are detecting a rich condition and telling the PCM to compensate by leaning out the mix. There is only so much wiggle room in the system, and the code is telling you that it has hit the low limit of compensation and is still being told to lean out the mix further. This could be happening because the MAF or TPS are failing or a number of other possibilities here including a very dirty air filter and dirty injectors. I think I've got that right but it's possible an expert will chime in here with a correction. If I'm wrong, I'm on the opposite side of the problem, in which case the problem could be a vacuum leak. Hear any weird hissing noises under the hood with the engine running? Is it idling high? Does it start within 1-3 seconds? Is the Intake Air Temperature sensor (inside the air filter box) intact and plugged in? Do you have a reusable oiled air filter?
    Mike

  8. #7
    Ranger's Avatar
    Ranger is offline Cadillac Owners Member
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    Re: Emmissions Codes

    Quote Originally Posted by mcowden
    The fuel trim system lean messages mean that the oxygen sensors are detecting a rich condition and telling the PCM to compensate by leaning out the mix. There is only so much wiggle room in the system, and the code is telling you that it has hit the low limit of compensation and is still being told to lean out the mix further. This could be happening because the MAF or TPS are failing or a number of other possibilities here including a very dirty air filter and dirty injectors. I think I've got that right but it's possible an expert will chime in here with a correction. If I'm wrong, I'm on the opposite side of the problem, in which case the problem could be a vacuum leak. Hear any weird hissing noises under the hood with the engine running? Is it idling high? Does it start within 1-3 seconds? Is the Intake Air Temperature sensor (inside the air filter box) intact and plugged in? Do you have a reusable oiled air filter?
    Mike,
    I may well be wrong but, I thought "Fuel Trim System Lean Bank 1 & 2" meant that a lean condition was detected.

  9. #8
    thehammer is offline Cadillac Owners Member
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    Re: Emmissions Codes

    Well I have no idea which one of you is right lean or rich, but I can answer your questions Mike:
    - No hissing
    - Idles around 500rpm from memory
    - Starts sweet every time

    But I have never checked the air filter - I will have a look this weekend.

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