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  1. #1
    Join Date
    Jun 2018
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    57

    Default 2007 xc70 half of the network down, CEM-df01 and df07, where to start?

    My friend and I got a used xc70 from auction. He is going to do the body work and im doing the rest. It was hit in the right rear, pretty light hit. Broke the lower tail and bumper and some trim.

    He drove it home, no heat or gauges.

    I scanned it with vida and found no network to the rear of the car after the CEM. The auction showed the gauges and miles working. But not when we picked it up. Maybe jumped backwards?

    Starts runs and drives, all fuses good in the engine bay, left side of dash and the rear electronic module. The REM is on the left side, not part of the accident.

    The three codes i get are CEM-DF01, CEM-E001 and CEM-DF07, all saying lowspeed network signal missing or faulty signal.

    The REM has 12v. VIDA says the REM powers the CEM.

    I guess i gotta get under the dash to explore the CEM.

    Id love some advice!

    Thanks.

  2. #2
    Join Date
    Nov 2018
    Location
    CT
    Posts
    76

    Default

    I wish I could be more helpful but it kind of sounds like a loose connector somewhere.

    I chased multiple seemingly unrelated codes in an S40 only to find out that a major connector wasn’t seated properly (even though it visually appeared to be).

  3. #3
    Join Date
    Jul 2012
    Location
    Landenberg, PA
    Posts
    247

    Default

    How's the battery? I know when my battery was getting towards the end of it's life, the car starting acting strange (throwing codes, random items not working) but it started fine. New battery cleared everything up.


    2005 XC70 - 50/35 Tint, Yakima Rack

  4. #4
    Join Date
    Jun 2018
    Location
    Vermont
    Posts
    57

    Default

    Vida said battery at 14.2 and charging system was normal.

    I used to work for mercedes, we had a whole CAN network fail because a back up sensor consumed road salt and failed. Since there was a rear sensor o. The back that was destroyed, i think ill disassemble the back and see whats pinched or cut.

    Also found some mouse poop, i hope its not a random chewed wire.

  5. #5
    Join Date
    Aug 2017
    Location
    Pleasanton CA USA
    Posts
    486

    Default

    This sounds like a CANbus glitch. The first thing the CEM does after start-up is to poll all the 40-or-so modules to assure each module is alive and serial communication is working. I believe your DTCs are arising during this module outreach. Since the CANbus is a common-wired bus, any short to 12V or ground anywhere on the signal wiring path will halt communications for the entire network. I've never debugged CANbus -- I've heard it's tricky. I would start by researching what is published on the topic.

    As an amateur, a general strategy might be:

    1) Unplug one harness at a time from the CEM. When the one with the signal problem is disconnected, the "signal fault" DTCs should disappear, and be replaced by "can't communicate with Modules X, Y, Z"

    2) Based on the accident damage, focus on unplugging modules whose CANbus wiring path might have been crunched in the collision.
    Last edited by pbierre; 11-14-2020 at 08:28 AM.
    2013 XC70 T6 Flamenco Red (hers)
    2015 XC70 T6 Seashell Metallic (his)
    past: 13 Volvos going back to '74 242 sedan

  6. #6
    Join Date
    Aug 2017
    Location
    Pleasanton CA USA
    Posts
    486

    Default

    Quote Originally Posted by Hamfist View Post
    Vida said battery at 14.2 and charging system was normal.

    I used to work for mercedes, we had a whole CAN network fail because a back up sensor consumed road salt and failed. Since there was a rear sensor o. The back that was destroyed, i think ill disassemble the back and see whats pinched or cut.

    Also found some mouse poop, i hope its not a random chewed wire.
    Rodents can get into tiny places....let's hope it's accident damage to wiring....more likely to be found.
    2013 XC70 T6 Flamenco Red (hers)
    2015 XC70 T6 Seashell Metallic (his)
    past: 13 Volvos going back to '74 242 sedan

  7. #7
    Join Date
    Jun 2018
    Location
    Vermont
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    57

    Default

    Where is the AEM module? The network diagram has that in grey, as in its not there. I mean its possible that this car wasnt built with it. Honestly not sure what it does, but it does show it has a home in the corner with the acxident damage. Does the AEM control the backup sensors, etc?

  8. #8
    Join Date
    Oct 2011
    Location
    Northshore - Great Lakes
    Posts
    813

    Default

    Quote Originally Posted by Hamfist View Post
    Where is the AEM module? The network diagram has that in grey, as in its not there. I mean its possible that this car wasnt built with it. Honestly not sure what it does, but it does show it has a home in the corner with the acxident damage. Does the AEM control the backup sensors, etc?

    FWIW, VIDA reading battery at 14.2V is actually alternator output. You want to warm up the engine, then turn off, and then read battery at the post with multimeter. VIDA drains battery.

    In our 2001 V70XC the REM is located at driver's rear in cargo area. https://youtu.be/TjkwLh_MHLQ

    2001 V70XC +204k miles/ XeMODeX/ Pirelli 12/32"/ Duracell 48/ MOBIL-3309/ Pennzoil EURO 5W-40/ Great Lakes

  9. #9
    Join Date
    Jun 2018
    Location
    Vermont
    Posts
    57

    Default

    Thats the REM, I found that and checked the fuses first and it has 12vdc going to it.

    Im looking for the AEM. Accessory equipment module. I havent found a good idea what it does, or exactly where it is but its pass side rear.

  10. #10
    Join Date
    Oct 2011
    Location
    Northshore - Great Lakes
    Posts
    813

    Default

    This can help a little with AEM use:

    https://parts.volvocarslisle.com/a/V...GR-257044.html
    2001 V70XC +204k miles/ XeMODeX/ Pirelli 12/32"/ Duracell 48/ MOBIL-3309/ Pennzoil EURO 5W-40/ Great Lakes

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