Humming sound coming from rear of car.
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Cadillac DTS Forum - 2006 through 2012 Discussion, Humming sound coming from rear of car. in Past Cadillac Vehicle Discussion; Tonight, while waiting for a friend, I noticed a humming sound coming from my trunk/rear. I was sitting idle for ...
  1. #1
    phigment is offline Cadillac Owners Fanatic
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    Humming sound coming from rear of car.

    Tonight, while waiting for a friend, I noticed a humming sound coming from my trunk/rear. I was sitting idle for about 30 minutes. Every two minutes or so I would hear a humming sound. My first thought is a fuel pump. It would run for approximately 10 seconds and then shut off. Ive noticed this sound in the morning when I first start my car but never continuously over and over again. I'm still having a problem where, while sitting at a stop light/drive through/other, the car coughs and stutters like a cylinder or two just stops working for a second. This never happens when in park or driving down the highway. The car is showing no codes. All of the injectors have been checked by a GM tech and they all show within spec. I've replaced all the plugs. Maybe a failing coil? I'm grasping at straws to connect the dots here. Any thoughts?

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    MoistCabbage's Avatar
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    I'm assuming the misfiring and humming don't happen at the same time?

    The humming sounds like the ELC (Electronic Level Control) pump. If it's running every few minutes, there's a leak in the system.

    The misfiring is a separate problem.

    Have the codes been pulled?

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    phigment is offline Cadillac Owners Fanatic
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    Re: Humming sound coming from rear of car.

    Thanks. It's not throwing any codes. Mine is a 2006. For some reason I didn't think this car had an ELC system. It has regular shocks in the back. At least I think.

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    Re: Humming sound coming from rear of car.

    I thought all dts models had air bags.

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    phigment is offline Cadillac Owners Fanatic
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    Re: Humming sound coming from rear of car.

    Are the air bladders located inside the rear shock? My car is at 131k miles now. I probably need to replace the rear shocks anyway. Is there anything special about the rear shocks? My local parts store show Monroe MA822 to be the replacements. Any opinions on those? I would like to go factory but the price is often prohibitive.

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    Submariner409's Avatar
    Submariner409 is offline If it won't run, stick on fender vents
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    Re: Humming sound coming from rear of car.

    The ELC system (ALL our cars) uses air bladders on each rear shock to compensate for added weight in the trunk or rear seat. The system is NOT "air ride", and it is NOT suspension control - it's level control only.

    The compressor (RR fenderwell area) should run for 2 - 3 seconds shortly after Key: ON and them unless weight is added, it should not again run again for that drive sequence.

    If the compressor cycles there's an air pressure leak - at the control head, the air lines, or the shock bladders. Car up on a lift, Key: ON, spray bottle of dish soap solution. Shocks, air lines wet - bubbles = leak.

    Original DTS ELC shocks are not cheap - be ready for excess sticker shock. There are cheaper, manual workarounds - basscatt has all the numbers, but you lose the DTS active suspension feature (constant handling and body control), but unless you enjoy "spirited driving" on occasion you might not notice the loss of control.

    More down in Cadillac Tech Tips - search through the pages of threads.

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    phigment is offline Cadillac Owners Fanatic
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    Re: Humming sound coming from rear of car.

    Local dealer cost is $322.00 each. My car is a LuxIII rather than sport. I don't think I have active suspension. So, will replacing the factory with the Monroe MA822 change anything for me? I've read the PDF under Cadillac Technical Archive named "Road Sensing Suspension System". It explains how the system(s) work but does not cover aftermarket parts. Anyone have any experience with the MA822's or should I just suck it up and drop the cash on OEM? Thanks again all.

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    Superjim's Avatar
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    Re: Humming sound coming from rear of car.

    Quote Originally Posted by phigment View Post
    Local dealer cost is $322.00 each. My car is a LuxIII rather than sport. I don't think I have active suspension. So, will replacing the factory with the Monroe MA822 change anything for me? I've read the PDF under Cadillac Technical Archive named "Road Sensing Suspension System". It explains how the system(s) work but does not cover aftermarket parts. Anyone have any experience with the MA822's or should I just suck it up and drop the cash on OEM? Thanks again all.
    If you have the part number for the OEM shocks... do an online search using the part number for better prices.

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    The Monroe MA822s are excellent shocks, I wouldn't even bother with the AC Delcos.

    The MA822s are the replacements for the last gen Sevilles and Devilles as well. If the AC Delco replacement is the same part for the DTS, it's a rebadged Gabriel Hijacker, which aren't the best shocks, and give a firmer ride.

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    Re: Humming sound coming from rear of car.

    $322.00 for OEM shocks isn't that bad. Compared to the $1000 it used to be for one shock. My 99 Seville had electronic struts in the front and electronic/air shocks in the back. They called it real time dampening suspension system.

    I believe the performance DTS have these kind of struts and shocks along with the magnetic ride control. I could be wrong. DO NOT BUY THOSE MONROE SHOCKS!!!! THEY ARE FOR TOWING AND HAULING AND WILL SEVERELY MAKE YOUR DTS RIDE FIRMER!!!

    You can buy the OEM shocks at GMParts Direct for $206.

  12. #11
    purelux is offline Cadillac Owners Fanatic
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    Any of the air assist shocks are for extra weight , allows a softer spring to be used then air as needed to maintain ride. I have the monroe ma822 on my 03 ride fine. Mc had a good point check if "oem" actually are or rebranded since acd may no longer produce them.

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    phigment is offline Cadillac Owners Fanatic
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    Re: Humming sound coming from rear of car.

    I purchased the MA822's from my local auto parts chain. I was going to install them today but they are much smaller and shorter than the factory shocks. Even fully extended they are much shorter. I've tried searching online but haven't found anybody who has installed these on a 2006+ DTS. Monroes website says they will work. Has anybody installed these on their DTS? Another question for the community. Will the shocks and struts from a Buick Lucerne fit the DTS?

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    I did installed them on my 06 dts they are the right length and it made the car ride better. If you don't like that very soft ride get them. Lso kyb makes them for our car.

  15. #14
    phigment is offline Cadillac Owners Fanatic
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    Re: Humming sound coming from rear of car.

    I just got through installing the MA822s. I've only driven it around the block. A few observations. The rear of my car seems to be sitting slightly lower than it did with the factory shocks. This could just be my imagination. The back end of my car, with the bad factory shocks, had a "bounce" to it. I could easily push down on the rear end and it would bounce back. With the new shocks there is a slight resistance when pushing down and the amount of travel has been reduced. For those of you who decide to change your shocks I will give some information that took me time to find. Do not remove the clips on the air line. They are a pain to get back on and you will probably disfigure the clip itself. Instead turn the connector/clip 90 degrees either clockwise or counterclockwise and then pull the connector off. If there is resistance just wiggle the connector and it will come off. At least it did for me. This may be obvious to some. I had to take a pair of pliers to the one clip I removed in order to get it back on and in the correct position. Also, in the previous post I stated that the Monroes were shorter than the OEM shocks. After I removed one of the old shock, I collapsed it completely. There is about a 2" difference eyeballing it. I'm guessing that 2" is negligible when the car is on the ground. Thanks to all for your responses to this thread.

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    MoistCabbage's Avatar
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    The shock itself does not dictate ride height. The ELC compressor runs (or the exhaust solenoid opens) until the ride height is correct. The height sensor is bolted to the body, and the connecting rod is attached to the lower control arm. The shock takes no part in that operation.

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