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Thread: LML VSS reading way high

  1. #1
    Junior Member
    Join Date
    Apr 2010

    Default LML VSS reading way high

    Hi Guys, Running out of idea's or things to try so thought i may put it out here.

    We have done a LML swap into another vehicle, Harness and ECM programming all done by Dmaxswap, Engine runs fine, But a speed limiter is kicking in at around 50 km/h road speed, This is because the ECM thinks (VSS on scanner) its doing over 255km/h.
    I have been talking to Adam about this, and he tried a few things in the tune with no change, He has basically now said its the VSS reluctor on the trans, But it cant be that, Trans output shaft RPM and gear shifts are correct based off road speed. TCM is seeing correct speed.

    The symptom is that the engine goes into throttle cut, Which we are quire confident is a speed limiter kicking in.
    Our VSS on scan tool is reading at least 4-5 times higher than it should, hence at around 50km/h road speed, ECM thinks its at 255 and cuts engine. I tried a stock tune file that had a lower cut in for limiter, and engine cut power at that lower speed. So basically we need to fix the VSS input to ECM.

    Changing the tyre size and diff ratio in ECM tune has no effect

    Changing tire size, diff ratio, etc in TCM has no effect on speed, But does change gear shift speeds.

    Changing reluctor tooth count in TCM does change speed, But also changes gear shift points and is not driveable.

    Our reluctor wheel is genuine Allison mounted to trans output shaft, 40 teeth, original speed sensor

    Ive confirmed the VSS input to the TCM is correct, Trans output RPM reads correct and gear shift positions are correct, at 50km/h road speed, 15% throttle, its in 3rd gear, if TCM thought is was doing 255 at 15% pedal (as ECM thinks) it would be in 6th

    I tried disconnecting the replicated TOS out of TCM, Thinking that would drop the signal like the older Duramax, But it doesn

  2. #2
    Lifetime Member comnrailpwr's Avatar
    Join Date
    Jun 2011


    Here is the issue I had a couple years back. This was not on I swap vehicle and it was just on a traditional daily driver 2013 LML. I have flashed a truck several times before without issues. He was returning just for a simple update. After flashing the truck the speedometer maxed out anytime key is on and the vehicles odometer reading started climbing extremely fast. I tried for about an hour with flashes and module reset to get the thing back to normal. The truck picked up about 12,000 miles in that hour and I never could get the speedometer off of Max. I don't remember the amount per hour. 220 or 250mph, somewhere around there. Our fix ended up being a replacement ECM and having the odometer adjusted back to where it needed to be.

    Sent from my SM-G960U using Tapatalk

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