2003 CTS ECM PCM Location
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Cadillac CTS First Generation Forum - 2003 - 2007 Discussion, 2003 CTS ECM PCM Location in Cadillac CTS Coupe, Sport Sedan and Sport Wagon Forums; Hi, My 2003 CTS was diagnosed with a bad PCM/ECM however the dealer is having a hard time finding one. ...
  1. #1
    donj808 is offline Cadillac Owners Member
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    2003 CTS ECM PCM Location

    Hi,
    My 2003 CTS was diagnosed with a bad PCM/ECM however the dealer is having a hard time finding one. I did find a used one, but I don't know if it can be self-installed. Could someone please let me know the exact location and how to remove/replace.

    Thanks,
    DJ

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  3. #2
    odysseus's Avatar
    odysseus is offline Cadillac Owners Connoisseur
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    Re: 2003 CTS ECM PCM Location

    The ECM on a 3.2L motor is mounted on a bracket right above the passenger side valve cover. Easy to get to, but they are VIN encoded like most of the other computers on the car, and you'll need your dealer to replace it so he can clear the VIN and relearn it before the engine will start. The factory shop manual dedicates 437 pages just to the ECM and engine controls!

  4. #3
    fastforward is offline Cadillac Owners Member
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    Re: 2003 CTS ECM PCM Location

    is the valve cover under the battery? How can I find it.

  5. #4
    Sammy Z's Avatar
    Sammy Z is offline Cadillac Owners Connoisseur
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    Re: 2003 CTS ECM PCM Location

    No, the valve cover is not under the battery. The ECM is on the passenger side of the engine. You may have to move the black rubber/plastic cover to get to it. There are two large connectors that plug into it. You have to move the lock clip on the connectors so you can remove them. Once you remove the connector, you will see the ECM.

  6. #5
    akeinc is offline Cadillac Owners Member
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    Re: 2003 CTS ECM PCM Location

    Quote Originally Posted by odysseus View Post
    The ECM on a 3.2L motor is mounted on a bracket right above the passenger side valve cover. Easy to get to, but they are VIN encoded like most of the other computers on the car, and you'll need your dealer to replace it so he can clear the VIN and relearn it before the engine will start. The factory shop manual dedicates 437 pages just to the ECM and engine controls!
    I got a question about weird scan tool readings:

    On my 2003 CTS I've been running the diagnostic tables for P0058, P0058, P0160 and P0161 (bank 2 sensor 2) codes using the AutoTap scan tool to see the HO2S signal voltage. I'm pretty sure I got a bad ECM as when I insert a test lamp between voltage and heater control the lamp doesn't illuminate when the engine is running thus the ECM is not commanding ground to the HO2S.

    I've triple checked all the related wiring for shorts and breakage and I can't find any anomalies except for when I run the scan tool. When I start the scan tool with the engine off I get the reference voltage (around 450) alright but when I poke and pull at the HO2S harness connector I get 20 to 50 mV spikes in the signal. Also with engine running the voltage does not change appropriately, it just stays in the same voltage range and randomly spikes plus or minus 50mV between the reference voltage, kind of looks like a heart EKG. When the engine fully warms up and enters loop it simply stays this way while bank 1 sensor 2 moves to lean and rich correctly (gradually).

    This occurs even since I removed the OEM connector and connected the HO2S (4th sensor) directly. I massaged each wire insulator and found that when I moved the insulation against the wire core of the High Signal wire on the last few inches of the run before the HO2S connector I'd get voltage spikes. The insulator was a little beat up with some core exposed so I replaced the latter eight inches of wire. I replaced the latter eight inches on the low signal wire as well. I dissected the wire and found it oil soaked (the valve cover gaskets leaked - a lot - since replaced) and corroded on the last few inches.

    That didn't seem to fix the problem. When I lightly poke at my new wire harness - same thing - 50 mV spikes. I've massaged all the other wiring runs related to this (I can reach all the wiring from the ECM to the HO2S) with no spikes. It all happens at the harness connection area by the HO2S. This happens with each wire physically separated with three of the wires with additional insulation added when connected to the HO2S. The wires that are moving are not touching each other.

    So not really having much experience with scan tools and voltage anomalies could this be another symptom of an ECM gone bad? Can environmental factors cause spikes (static electricity)?

    ---

    Extra info:

    This is my 4th HO2S sensor at this location. I replaced all the HO2S sensors with the Bosch generic and tested the bad location with the other old OEM sensors with the same results.

    I just pulled a sensor off that had been running for about 10k miles and the heater core was broken. The heater core had been broken on the original OEM and the first Bosch replacement. In other words every sensor I run at this location for any period of time breaks the heater core. Weird since the core isn't being commanded to ground by the ECM as far as I can tell.

    I've also run the diagnostic for P0160 which has you jump the low and high signal and read the voltage on the scan tool which the ECM passes. The threshold when jumped is 25mV. Less is fail more is pass. I get around 300mV. Fail sends you to the inspect HO2S for contamination page.

    I've also crossed the sensor connections (bank 1 SENSOR 2 to bank SENSOR 2).

    Thanks:

    Don

  7. #6
    txbest1980's Avatar
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    Re: 2003 CTS ECM PCM Location

    the god awful P0160 and P0161 codes. i had this problem as well and traced it and traced it. couldnt find anything until i decided to say let's try a new ECM. hooked up a new ECM and viola it worked like a charm and my Check Engine Light was gone for good.

  8. #7
    akeinc is offline Cadillac Owners Member
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    Re: 2003 CTS ECM PCM Location

    Quote Originally Posted by txbest1980 View Post
    the god awful P0160 and P0161 -BREAK - couldnt find anything until i decided to say let's try a new ECM.
    I'm not the only one, phew. I'm really close to doing the ECM swap except for the weird voltage when I jiggle the wires and I'm hoping somebody with experience can allay my fears.

    HeyTx, did you have the dealer swap out your ECM? I'm at 120,006 miles so I'm figuring $445.22 plus an hour of labor for both the replace and reprogram.

    Don

  9. #8
    txbest1980's Avatar
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    Re: 2003 CTS ECM PCM Location

    i refuse to go to my local stealership. they are absolutely useless. so i drove my car to my trusty mechanic who can flash ECM to cars, and i pulled it into his shop, swapped out the ECM and then he went to work. i paid him @ $50 to reflash for me. that took about two to three hours cause of all the process that need to be relearned, and then i was on my way. you can get the ECM for much cheaper from www.gmpartsdirect.com

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    akeinc is offline Cadillac Owners Member
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    Re: 2003 CTS ECM PCM Location

    Oh whoa wow, www.gmpartsdirect.com, way cheaper, over $220 less! Thanks for that link Tx. When looking for a mechanic to program your car, what tool do they need? Is it the "Tech 2"? I thought only dealers had the proprietary rights and licensing to our computers. I am ignorant of these automotive DRM corporate ownership schemes.

  11. #10
    Coke_O is offline Cadillac Owners Fanatic
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    Re: 2003 CTS ECM PCM Location

    Quote Originally Posted by txbest1980 View Post
    i refuse to go to my local stealership. they are absolutely useless. so i drove my car to my trusty mechanic who can flash ECM to cars, and i pulled it into his shop, swapped out the ECM and then he went to work. i paid him @ $50 to reflash for me. that took about two to three hours cause of all the process that need to be relearned, and then i was on my way. you can get the ECM for much cheaper from www.gmpartsdirect.com
    txbest, you live in houston right? which mechanic do you take your car to? I really need to get my 03 3.2L checked out.

    Thanks.

  12. #11
    txbest1980's Avatar
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    Re: 2003 CTS ECM PCM Location

    Quote Originally Posted by akeinc View Post
    Oh whoa wow, www.gmpartsdirect.com, way cheaper, over $220 less! Thanks for that link Tx. When looking for a mechanic to program your car, what tool do they need? Is it the "Tech 2"? I thought only dealers had the proprietary rights and licensing to our computers. I am ignorant of these automotive DRM corporate ownership schemes.
    not only dealerships have these machines, any shop that is truly doing complete car care will have these machines as well. call around and check to see if they can reprogram/reflash an ECM for ya. it will be cheaper than going to the dealership

  13. #12
    txbest1980's Avatar
    txbest1980 is offline Cadillac Owners Master
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    Re: 2003 CTS ECM PCM Location

    Quote Originally Posted by Coke_O View Post
    txbest, you live in houston right? which mechanic do you take your car to? I really need to get my 03 3.2L checked out.

    Thanks.
    well i have a personal guy who works for David Taylor when i am there in the area. i am actually from galveston, but i am active duty military. and uncle sam so chooses for me to be in Tucson AZ right now. but anyways, i can get you his contact number if you are interested...also, what exactly is wrong with your car?

  14. #13
    akeinc is offline Cadillac Owners Member
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    Re: 2003 CTS ECM PCM Location

    Made a basic physics mistake. Followed diagnostic table without considering that the lamp test would not be accurate with another lesser path to resistance present so I disconnected both downstream O2 sensor heater circuits and connected them to EQUAL wattage lamps. It seems that both O2 sensors are receiving ground appropriately: short pulses when warming up and continuous with short interruptions to test reference voltage once warmed up. I've included a couple videos to demonstrate.





    Even without the heater circuit connected the HO2S sensors (lamps only) both downstream O2 sensors operate as before: bank 1 operates normally and bank 2 operates with a continuous erratic voltage.

  15. #14
    Coke_O is offline Cadillac Owners Fanatic
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    Re: 2003 CTS ECM PCM Location

    Quote Originally Posted by txbest1980 View Post
    well i have a personal guy who works for David Taylor when i am there in the area. i am actually from galveston, but i am active duty military. and uncle sam so chooses for me to be in Tucson AZ right now. but anyways, i can get you his contact number if you are interested...also, what exactly is wrong with your car?
    rough idling. random "engine power reduced" and turning off while driving or sitting at a light. rough shifting. I've tried cleaning the throttle body, replacing it, replacing the crankshaft position sensor, seafoam. I don't know what else to try.

  16. #15
    Coke_O is offline Cadillac Owners Fanatic
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    Re: 2003 CTS ECM PCM Location

    @txbest ok, just finished cleaning the throttle body. so far so good. Thanks man.

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