Lift/Dive signal from PCM?
Cadillac
 

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds / (Old System)

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors

CadillacForums.com is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Results 1 to 15 of 15
Suspension, Brakes and Tires Discussion, Lift/Dive signal from PCM? in Item Specific Cadillac Discussion; I was looking through some diagrams, and I noticed the Lift/Dive signal is generated from the PCM in most cars. ...
  1. #1
    DaveSmed's Avatar
    DaveSmed is offline Cadillac Owners Connoisseur
    Automobile(s): 1968 Cadillac Sedan deVille, 1994 Chevrolet G20
    Join Date
    Aug 2003
    Location
    Bucks County, PA
    Age
    27
    Posts
    2,795

    Lift/Dive signal from PCM?

    I was looking through some diagrams, and I noticed the Lift/Dive signal is generated from the PCM in most cars. Anyone know how this signal is determined? I know lateral acceleration is a seperate switch connected to the RSS/SSS module. I was wondering if these outputs could be used for anything else.

  2. Remove Advertisements
    CadillacForums.com
    Advertisements
     

  3. #2
    Krashed989's Avatar
    Krashed989 is offline Cadillac Owners Connoisseur
    Automobile(s): 94 Eldorado, and a 99 ETC
    Join Date
    Sep 2004
    Location
    Hilo, Hawaii
    Age
    27
    Posts
    3,887

    Re: Lift/Dive signal from PCM?

    The lift/dive signal is not generated from the PCM. The wheel position sensors contain variable resistors in them that will change the feedback voltage to the RSS module relative to the position of the wheel. The RSS module then reads that voltage and compares it to the other sensors readouts to find the vehicles pitch and also how far the vehicle is swaying in turns. It uses the data to know when to engage the dampering valves in each shock and strut and also to know what rear shock to pump up with air when in a turn.

  4. #3
    Katshot's Avatar
    Katshot is offline Cadillac Owners Master
    Join Date
    Jan 2003
    Location
    Newtown, PA
    Age
    55
    Posts
    6,472

    Re: Lift/Dive signal from PCM?

    Quote Originally Posted by Krashed989
    The lift/dive signal is not generated from the PCM. The wheel position sensors contain variable resistors in them that will change the feedback voltage to the RSS module relative to the position of the wheel. The RSS module then reads that voltage and compares it to the other sensors readouts to find the vehicles pitch and also how far the vehicle is swaying in turns. It uses the data to know when to engage the dampering valves in each shock and strut and also to know what rear shock to pump up with air when in a turn.
    I don't recall the RSS cars having individual air lines to the rear shocks. I'll have to check my diagrams.

  5. #4
    DaveSmed's Avatar
    DaveSmed is offline Cadillac Owners Connoisseur
    Automobile(s): 1968 Cadillac Sedan deVille, 1994 Chevrolet G20
    Join Date
    Aug 2003
    Location
    Bucks County, PA
    Age
    27
    Posts
    2,795
    Thread Starter

    Re: Lift/Dive signal from PCM?

    Quote Originally Posted by Krashed989
    The lift/dive signal is not generated from the PCM. The wheel position sensors contain variable resistors in them that will change the feedback voltage to the RSS module relative to the position of the wheel. The RSS module then reads that voltage and compares it to the other sensors readouts to find the vehicles pitch and also how far the vehicle is swaying in turns. It uses the data to know when to engage the dampering valves in each shock and strut and also to know what rear shock to pump up with air when in a turn.
    I know the CVRSS systems used the wheel position sensors, but I didn't think the plain RSS systems did. I know the SSS systems do not. The SSS and RSS has some input from the PCM labeled Lift/Dive.



    Also, I am pretty sure the rear air shocks are based off of a seperate single position sensor off of one control arm, and it is delayed so as to not attempt adjustment due to suspension movement, due to the slow action of the compressor.

  6. #5
    Krashed989's Avatar
    Krashed989 is offline Cadillac Owners Connoisseur
    Automobile(s): 94 Eldorado, and a 99 ETC
    Join Date
    Sep 2004
    Location
    Hilo, Hawaii
    Age
    27
    Posts
    3,887

    Re: Lift/Dive signal from PCM?

    Hmmm, you've raised my curiosity now. I'm gonna have to look into it.

  7. #6
    peteski is offline Cadillac Owners Enthusiast
    Automobile(s): 85 Eldo Biarritz
    Join Date
    Dec 2003
    Location
    Northeast USA
    Posts
    808

    Re: Lift/Dive signal from PCM?

    IIRC, (on my 93 Eldo TC with RSS suspension) that singnal is actually gennerated by the PCM (and it is an input to the RSS module). Just as the diagram in the above post shows.

    Reading the circuit description I think that it mentions that PCM generates that signal from several inputs (none of which are related to any suspension components). Basically, it determines lift/dive from things like change in speed, throttle position, gear selection and "brakes applied" signals.

    Also RSS dosn't have lateral accelerometer. Only SSS has one. This is all covered in the HELM manual. You just have to read through those chapters...

    Katshot mentioned that RSS cars dont' have individual lines to the air shocks. That is false and doesn't make sense. Yes, both rear airshocks have single separate air line attached to each shock. They both end up at the compressor.

    Remember, the air is not what controls the shock stiffness - it is the solenoid controlled valve in each shock.

    Peteski

  8. #7
    DaveSmed's Avatar
    DaveSmed is offline Cadillac Owners Connoisseur
    Automobile(s): 1968 Cadillac Sedan deVille, 1994 Chevrolet G20
    Join Date
    Aug 2003
    Location
    Bucks County, PA
    Age
    27
    Posts
    2,795
    Thread Starter

    Re: Lift/Dive signal from PCM?

    That makes sense, probably closely monitors the rate of change from the VSS especially. RSS has no lateral accelerometer? Does it determine cornering forces via another secondary method (like the lift/dive signal) or is there no input at all for that? The Cadillac electronic suspension system interests me for some reason, probably because of all the engineering that goes into a feature that is either rendered obsolete due to parts constraints. Wonder if all that technology can be applied to something else? Off the top of my head, maybe something to record if someone was driving your car in a "spirited" manner outside of your supervision? Hmm...

    Oh, and I think Katshot was referring to the common control for both rear air shocks, as in they cant be seperately adjusted.

  9. #8
    Krashed989's Avatar
    Krashed989 is offline Cadillac Owners Connoisseur
    Automobile(s): 94 Eldorado, and a 99 ETC
    Join Date
    Sep 2004
    Location
    Hilo, Hawaii
    Age
    27
    Posts
    3,887

    Re: Lift/Dive signal from PCM?

    Here it is, as quoted from All Data:

    "The lift signal is calculated in the PCM and is based on throttle position, vehicle speed and transmission gear. The dive signal, also calculated in the PCM, is based on rate of change of vehicle speed."

    Well, now I can say I learned something today.

    I know RSS does have four accelerometers. I'm not sure if they measure lateral forces though.


    Yes, the rear shocks both have an individual air line going to them; otherwise, it wouldn't be able to 'level out'. It would just end up raising or lowering the entire rear end instead. You can test this by simply putting your spare tire on, in place of one of your rear wheels. After a short drive you will see that the shock on that side will be almost completely extended, and it will be even more noticable when you put the regular wheel back on there and see that the car is tilted to the other side.

  10. #9
    Katshot's Avatar
    Katshot is offline Cadillac Owners Master
    Join Date
    Jan 2003
    Location
    Newtown, PA
    Age
    55
    Posts
    6,472

    Re: Lift/Dive signal from PCM?

    Quote Originally Posted by DaveSmed
    Oh, and I think Katshot was referring to the common control for both rear air shocks, as in they cant be seperately adjusted.
    Thanks Dave, that's what I was trying to say alright. There's only one airline that connects to the compressor. One shock generally has 2 ports and the other has one. The airline usually connects to the shock with 2 ports and then that shock connects to the other. So in essence the two shocks are supplied via one airline and are not individually adjustable. And yes I realize the RSS system only controls shock dampening rates.

  11. #10
    Krashed989's Avatar
    Krashed989 is offline Cadillac Owners Connoisseur
    Automobile(s): 94 Eldorado, and a 99 ETC
    Join Date
    Sep 2004
    Location
    Hilo, Hawaii
    Age
    27
    Posts
    3,887

    Re: Lift/Dive signal from PCM?

    Quote Originally Posted by Katshot
    Thanks Dave, that's what I was trying to say alright. There's only one airline that connects to the compressor. One shock generally has 2 ports and the other has one. The airline usually connects to the shock with 2 ports and then that shock connects to the other. So in essence the two shocks are supplied via one airline and are not individually adjustable. And yes I realize the RSS system only controls shock dampening rates.

    That must be a different system you're talking about because RSS does have an individual line for each shock from the compressor. I remember looking at them when changing my shocks (94 eldo w/n*).

  12. #11
    Katshot's Avatar
    Katshot is offline Cadillac Owners Master
    Join Date
    Jan 2003
    Location
    Newtown, PA
    Age
    55
    Posts
    6,472

    Re: Lift/Dive signal from PCM?

    Someone may have installed a "tee" connection when installing aftermarket shocks. It's actually a very common practice since even if you used Delco shocks from a parts store they would only have one fitting per shock. This would necessitate the installation of an accessory kit and some air line. The only way around doing this is to use factory replacement units FROM THE DEALER. Most people think that Delco is Delco but it's not true. There's Delco OEM and then there's Delco Aftermarket. Most of the parts are the same but some are different. Such is the case with the Cadillac airshocks. They come from the factory with two fittings on one shock and one fitting on the other. The Delco (factory replacement) shocks you'd buy at a delco distributor will have one and one.

  13. #12
    Krashed989's Avatar
    Krashed989 is offline Cadillac Owners Connoisseur
    Automobile(s): 94 Eldorado, and a 99 ETC
    Join Date
    Sep 2004
    Location
    Hilo, Hawaii
    Age
    27
    Posts
    3,887

    Re: Lift/Dive signal from PCM?

    Quote Originally Posted by Katshot
    Someone may have installed a "tee" connection when installing aftermarket shocks. It's actually a very common practice since even if you used Delco shocks from a parts store they would only have one fitting per shock. This would necessitate the installation of an accessory kit and some air line. The only way around doing this is to use factory replacement units FROM THE DEALER. Most people think that Delco is Delco but it's not true. There's Delco OEM and then there's Delco Aftermarket. Most of the parts are the same but some are different. Such is the case with the Cadillac airshocks. They come from the factory with two fittings on one shock and one fitting on the other. The Delco (factory replacement) shocks you'd buy at a delco distributor will have one and one.

    That's impossible, because my parents owned this car since it was new, and the first time the shocks were touched was when I replaced them. Even the old OEM shocks (yes, I replaced them with aftermarket, but no modifications were made to the lines) that were on there had only one fitting per shock. I'll see if I can take pictures for you tomarrow.

    What diagrams were you looking at to see the air line routing?


    Quote Originally Posted by Krashed989
    Yes, the rear shocks both have an individual air line going to them; otherwise, it wouldn't be able to 'level out'. It would just end up raising or lowering the entire rear end instead. You can test this by simply putting your spare tire on, in place of one of your rear wheels. After a short drive you will see that the shock on that side will be almost completely extended, and it will be even more noticable when you put the regular wheel back on there and see that the car is tilted to the other side.
    BTW, this does work because I've had flat tires before and have seen it do this.

  14. #13
    peteski is offline Cadillac Owners Enthusiast
    Automobile(s): 85 Eldo Biarritz
    Join Date
    Dec 2003
    Location
    Northeast USA
    Posts
    808

    Re: Lift/Dive signal from PCM?

    Katshot might be confusing electrical wiring with air lines going to the shocks.

    Cars with RSS (aka. RTD) have the following:

    Rear: Each air adjustable shock has a single wire harness and a single air line going to it . Air is used only for leveling the car. Electrical is used only for controling the stiffness of the shock.

    Front Struts: no air lines and a single wire harness going to each. It controls the stiffenss of the strut.

    Actually, the SSS equiped cars will have same number of connections. But the actual shocks/struts are a bit different.

    Some older Caddies had a single connection to one shock and a dual on the second one. My 85 Eldo is like that.
    But my 93 Eldo has a single air connection on each rear shock.

    As far as lateral acceleration goes, I suspect that RSS calculates that from the position of all 4 of the wheel position sensors. If wheels one side of the car are higher then the other, then the car must be in a turn. The the difference in height and car's speed can probably be used to calculalte lateral acc. The vertical accelerometers also probably provide some data to arrive at the final value.

    Since the SSS cars don't have wheel position sensors, they need the lateral accelerometer.

    I have no clue how you conducted the "spare tire" experiment. There is only one compressor and one exhaust solenoid. There is no way to individually control pressure going to each shock. Impossible.

    Peteski

  15. #14
    Krashed989's Avatar
    Krashed989 is offline Cadillac Owners Connoisseur
    Automobile(s): 94 Eldorado, and a 99 ETC
    Join Date
    Sep 2004
    Location
    Hilo, Hawaii
    Age
    27
    Posts
    3,887

    Re: Lift/Dive signal from PCM?

    Quote Originally Posted by peteski
    ...I have no clue how you conducted the "spare tire" experiment. There is only one compressor and one exhaust solenoid. There is no way to individually control pressure going to each shock. Impossible....
    Valves maybe?

  16. #15
    peteski is offline Cadillac Owners Enthusiast
    Automobile(s): 85 Eldo Biarritz
    Join Date
    Dec 2003
    Location
    Northeast USA
    Posts
    808

    Re: Lift/Dive signal from PCM?

    Nope - no valves... Single air circuit. And Service Manual confirms that fact.

    Peteski

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.
If you do not want to register, fill this field only and the name will be used as user name for your post.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Bookmarks

Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting