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4L80e experts? SOLVED


...no more! Call me Murphey
St. George
Having some issues with a gm swap. It is a TBI 5.7 and early 4l80e, Howell stand alone harness so it is simple and not a mess of wires, all new, clean and runs good.

Issue I'm running into is I only had 1st, 2nd and reverse no DTC codes. After some others shared some input, I looked into the DRAC module and if it doesn't see "X" amount of pulses per mile this can happen. So used the calculation to compensate for axle ratio and wheel circumference, got my jumper layout how it needs to be in the DRAC changed. Now I can get it to shift to 3rd, but late (like 5k rpms) and then when I get back to the driveway and check code, I have DTC 24 see below. SO it seems like progress with the DRAC modification, but not really lol.

CODE 24 - VSS (Vehicle Speed Sensor)

Trouble Code 24 indicates that the Vehicle Speed Sensor (VSS) is reporting an abnormally low reading when other sensors indicate it should be higher.

The conditions for setting this code are:
  • no Code 33 or 34 (MAF Error) is present, and
  • the vehicle speed signal indicates < 4 MPH and
  • engine speed is between 1400 and 4400 RPM, and
  • during a low load condition (LV8 between 50 and 99), and
  • transmission not in Park or Neutral, and
  • all conditions met for more than 20 seconds
If the code was logged when the vehicle was in motion, the following should be checked:

1) Defective or corroded VSS connections
2) Maladjusted TPS sensor. The TPS should read about 0.42 volts at closed throttle
3) Defective speedometer cable
4) Bad or missing speedo drive gear(s) in tail shaft housing of the transmission
5) Defective VSS
6) Defective ECM

Replaced both sensors (input and output) on the driver side trans body, but get same thing as with old sensors. TPS tests good, Power to DRAC is good, Power to Trans main connector is good.

Anyone have any experience or more knowledge than I on how to get this trans to work properly? Am I missing something? Don't have/have access to scanner so not sure what computer is saying to command, wave patterns etc.

Thanks in advance.


...no more! Call me Murphey
St. George
Solved! So, after weeks of looking at pics, reading others threads, chasing wires, comparing old harness to new, and much more, the Howell harness for these applications (h9395) is correct, but wrong lol. The pinout is all correct, but according to their GM schematic B5,6 are labelled for the indicator to the ECU that the vehicle is in 4wd (so as not to throw off the dash speedo or give a false limp mode). This is, in my case anyway, not true, B9,10 is high/low signal for the 4l80e (front/red,blue) input sensor, B11 is ECU signal wire, B5,6 is 4l80e (rear light blue/green) output sensor NOT 4WD indicator-ground to activate as labelled. Green/purple is NOT for output sensor, but for T-case speed sensor. Not sure why there is discrepancy from the GM schematic, but its aged me a few years trying to figure this out lol. Props to Howell though for making a great harness and backing it up with lots of emails and phone time to get this running!


But stuck more often.
I had a similar experience with a Novak LS1 wiring harness where they pinned a few wires in the wrong spots on the ECM plugs. Drove me crazy trying to figure that one out. You never expect brand new wiring to be the issue.