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2005 RXT DESS ECU or MPEM problem? Help please!

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  • 2005 RXT DESS ECU or MPEM problem? Help please!

    2005 RXT - bone stock and gently run. Sorry, this is my first time posting on a forum, so be gentle.

    For years the ski would give me one long beep instead of two short about 10% of the time. It would start eventually anyway by repeatedly pressing the start button or reinstalling the key until I got the correct two beeps from the DESS. The problem at startup has gotten worse over the years and now it gives me two beeps only 10% of the time and it finally left me stranded on the water.

    Now to get it to started I have to install the key, it gives me one long beep, then I repeatedly hit the start/stop button until it cranks up. Sometimes this takes 30 seconds. Sometimes 10 minutes. Once it fires up it runs flawlessly, like the day it was new.

    Details -
    235 hours
    new battery
    DESS post tests good
    starter solenoid tests good
    wires, connectors, grounds, all clean and tight
    DESS key well worn but clean - when I plug in an old key from another ski the cluster shows ÔÇ£key.ÔÇØ That never happens with the mated key, so I assume it's okay.
    Code check shows only one code - P1517 Compass out of range. On startup blinks ÔÇ£SensorÔÇØ (compass?) and "Maint" (SC rebuild is due again), then runs and displays normally.

    Here's my plan with the limited knowledge I have:
    Purchase a CandooPro and a new DESS key - reprogram both keys and see if if solves the problem. If no,
    Crack open the ECU and see if I can locate/clean the short. if no,
    Purchase a used ECU #664947, use Candoo to mate ECU/cluster/MPEM, reset TPS and installed options

    Questions -
    My feeling is this intermittent DESS problem is being caused by the ECU, could it be the MPEM? Is their anyway to isolate this with or without the Candoo?
    Can I open the ECU and see if the board is being shorted intermittently? If so, how do I crack this box open?
    Does anyone sell used CandooPros with 1, 2, or 3 licenses remaining at a discount?
    Does anyone out there have a used CEU #664947?
    Any other 215 hp part numbers that will work for CEU #664947?

    My dealer in Sarasota/Venice closed several years ago and I really don't want to drag this thing to Bradenton or Tampa.
    Can the Candoo perform all the functions I need to swap out a new or used ECU (or MPEM) without a trip to a dealer?

    Thanks in advance guys!


  • #2
    Dess post's and harnesses are often the culprit when someone is having issues such as yours, to diagnose the problem it helps to have a basic understanding of how the system works but I'll give you the short version and ask away if you have specific questions.

    The post and key have two essential functions to signal the MPEM/ECU to unlock the security and allow the start/stop switch to power up the starter motor relay, the key magnet closes the reed switch in the post and provides a path to ground back to the modules at which time the ECU is looking for the Dallas IC chip code stored in the lanyard cap over the low voltage communication wire.

    Let's see if your's is working reliably, all you need is a test meter along with a small magnet (back of a refrigerator magnet works well) and a spare set of steady hands. What you want to accomplish in this test is mimicking the function of the key magnet opening the reed switch in the post while still being able to probe the contacts on the DESS post.

    1. Set your meter to test for 12VDC
    2. Have your helper hold that magnet right on the plastic shoulder of the DESS post.
    3. Probe the metal ring under the post shoulder with your negative lead and the center top contact dot with the positive and report back with the voltage reading.
    Offering carburetor & fuel injection service~ Sea Doo DESS & RF key programming~MPEM/ECU diagnostic service available on all BRP products ~Sea Doo shop tools available for rent serving Northern IN and SW Michigan


    • #3
      Thanks for the reply Waterluvr. It would be great if you were right. I agree the DESS components and connections are naturally suspect based on the symptoms. I got back out on the water this afternoon and had the usual starting problem.

      I understand the basics of the DESS system and tested the safety lanyard switch using the 4-tech-shop-manual.

      The test from Bombardier is "disconnect the switch wires and with the lanyard removed, test probe black and black/yellow wires and measure resistance. There should be NO continuity (open circuit). Connect one test probe to the WHITE/GREY wire and the other to the switch top terminal and measure resistance. It must be close to 0 ohm. Connect one test probe to the BLACK wire and the other to the switch ring and measure resistance. It must be close to 0 ohm. With the safety lanyard ON the switch, connect test probes to BLACK and BLACK/YELLOW wires and measure resistance. It must be close to 0 ohms."

      The switch tested out okay according to the manufacturer.

      I performed your test as described. When the switch closes with a magnet, according to my meter it throws 3.66 volts between the terminal top and ring. I repeated it a dozen times and got the same voltage each time.

      Thanks again for your help!


      • #4
        Ok, the magnetic function of the key and post are all in good order and the module is definitely getting a ground from the reed switch and waking up to look for the key code, it's not seeing it over the communication line reliably.

        The Dess system runs on Maxim one wire protocol tech and issues with the communication line effect the timing speed and the modules ability to see the key.

        Two usual suspects in that case:

        1. The stranded wire in the Dess post harness on the low voltage line will cause this and no amount of resistance testing will justify it as you'll get near perfect readings on a wire that's been pinched or otherwise compromised up under the potting at the post connection that still will show you near perfect continuity.

        One or two strands of wire in good order remaining in the original circuit will fool you every time, just plugging in a known post and harness is really the only way to rule it out it's a very common problem on aging ski's and boats.

        2. Key's can develop issues over time, if you have a quality autoranging meter take a continuity test by probing either of the sidewall contacts inside the key with the red lead and probe the top center contact in the cap with the black lead. Keys that function reliably 100% of the time will have around 7.5-8.5 M (Megaohms on the 0.000001 scale) and keys with higher readings become less dependable as that interferes with communication timing.

        Keys much over 18.5 are normally problematic or no longer function with the module at all.
        Offering carburetor & fuel injection service~ Sea Doo DESS & RF key programming~MPEM/ECU diagnostic service available on all BRP products ~Sea Doo shop tools available for rent serving Northern IN and SW Michigan


        • #5

          This is great detail on testing on the DESS system!

          Unfortunately, I have been unable to find an autoranging meter that will provide a way to test the keys. I did find a speed shop close by that will program a new key for me for $30. I'll get over there in the next few days and see if it solves the issue.

          Your comments about how worn wiring could cause communication delays and erratic performance make a lot of sense. I had a similar problem when the cluster went dead. I was able to solder in a new communication wire from the cluster connector to the back of the MPEM and it's worked perfect ever since.

          If a new key doesn't provide a fix could I temporarily solder in a new wire direct from the back of the switch to the CEU to test the wiring comms?



          • #6
            Try the key first, you might get lucky and that will handle the issue that's a reasonable price for programming. If that doesn't get it taken care of I'd swap out the DESS post and wiring for new at that point.

            I have several dess posts and harnesses out in the shop made up with all the connector ends BRP used over the years it's amazing how many times just unplugging the old one and swapping in a replacement shows you the one in the ski is bad no matter how well they test.
            Offering carburetor & fuel injection service~ Sea Doo DESS & RF key programming~MPEM/ECU diagnostic service available on all BRP products ~Sea Doo shop tools available for rent serving Northern IN and SW Michigan


            • #7
              Finally got the ski to Wade Chapin Performance. New DESS key solved the communications problem. All is perfect once again.

              Got one new key, two keys programmed (one as a Learning Key limited to 35 mph), codes cleared with a history list, and Maintenance timers reset, all for under $100 while I waited.

              Highly recommend Wade Chapin Performance in Sarasota. It looks like he works on all 4 stroke PWCs.

              Thanks again for your kind diagnostic help Waterluvr!