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Back to square one.....any ideas?

Pornstarr Jul 17, 2008

  1. Pornstarr

    Pornstarr Member

    So, a little while ago I replaced my G42 sensor.
    It's the combined Boost and charge temp sensor that sits in the top of the throttle body boot (B5 S4).

    I did this because it appeared to be at fault. Engine was intermittently reading 143 degrees charge temp....even at idle and with the engine off.
    Then it went to reading it permanently.

    Anyway, changed the sensor, and the problem went away!

    Until now.....
    And it's come back....

    Almost permanently!

    You'll be driving along, and suddenly get a massive surge of power. Or go to pull out of a junction and almost totally overshoot it, because suddenly the sensor is reading right, and the car's at full power.

    It's absolutely frustrating to the core.

    Other than thinking it's a wire that's gone high resistance, or is shorting somewhere....what else could it be?

    I've had the Y pipe off today, and checked as much of the wire as I can, which isn't much as it's all 'loomed' in with everything else. And I can't see where it might be broken/chafing/high res.

    Anyone had this before?
    How did you fix it?
  2. Blue_Thunder

    Blue_Thunder Well-Known Member

    As I was reading this the first thought I had was a knackered wire as well, as i've never heard of a MAP sensor failing on an S4 before.

    Might be worth taking it to an auto electrician to see what they can find if you can't find anything.
  3. aragorn

    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

    what i'd do is find where each wire comes out on the ECU plug and get a meter across it, then wiggle the harness around to see if i could make the circuit break.

    Hopefully you can narrow down the break by watching where the movement causes the meter to drop out and if you cant narrow it down but it is at fault you could always bypass the whole wire
  4. Pornstarr

    Pornstarr Member

    It's definately not high res. at the sensor end.
    So must be further back in the harness.

    I'll have to take a day out somewhere and have the top of the engine apart to get access to as much of the wire as poss.

    In my mind, it's either along the top of the engine due to heat. Though the other wires would surely be affected too.

    Or, it's along the top of the engine/at the back of the engine, where the wiring harness has been removed previously to gain access to remove the engine or something and the wires have been pulled/damaged by clumsy/lazy workmanship?

    Bypassing the whole wire would be an absolute nightmare, and take ages to get it to look right. Patching a new section in would be easier.......

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