Silverado ABS light causes 500 rpm short shift
12-24-2016, 10:30 AM
#1
Silverado ABS light causes 500 rpm short shift To all,
Weird problem on E38 ECM Silverado. Has happened every time I've taken truck to strip but never on the street. Go through burnout, launch and sometime towards the top of 1st the ABS light comes on and will cause the trans to short shift by about 500rpm before the 6000 rpm redline in each gear. No wheel spin from the hole and doesn't come on during the burnout where you would think it would due to no vehicle movement but wheel spin. Again, never happens on street launching or spinning tires.
My question is whether something in tune can be adjusted to stop the short shift? Truck has no traction control button. Pulling ABS fuse did not help as pulling fuse obviously causes light to come on and same short shift.
Don't have my Autocal back yet from getting a wide band port added so I couldn't log.
If anyone has seen a similar problem or fix, let me know. Thanks for the time.
Adam
Weird problem on E38 ECM Silverado. Has happened every time I've taken truck to strip but never on the street. Go through burnout, launch and sometime towards the top of 1st the ABS light comes on and will cause the trans to short shift by about 500rpm before the 6000 rpm redline in each gear. No wheel spin from the hole and doesn't come on during the burnout where you would think it would due to no vehicle movement but wheel spin. Again, never happens on street launching or spinning tires.
My question is whether something in tune can be adjusted to stop the short shift? Truck has no traction control button. Pulling ABS fuse did not help as pulling fuse obviously causes light to come on and same short shift.
Don't have my Autocal back yet from getting a wide band port added so I couldn't log.
If anyone has seen a similar problem or fix, let me know. Thanks for the time.
Adam
12-24-2016, 01:08 PM
#2
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More likely a common cause for both, like maybe a
flaky VSS (or harness) that freaks out both ABS
brain and transmission shifting functions of the PCM.
But don't believe the taco-meter, neither.
Look for immature codes after such an event, for
weird MPH readings just before.
You can also get short shifting by having too high
a TPS voltage (would happen only at WOT, maybe
your burnout doesn't hit shift point or max throttle
angle, so you just don't see it).
But first question whether it's the RPM that's short,
or its indication (dash tachs are notoriously slow /
late).
flaky VSS (or harness) that freaks out both ABS
brain and transmission shifting functions of the PCM.
But don't believe the taco-meter, neither.
Look for immature codes after such an event, for
weird MPH readings just before.
You can also get short shifting by having too high
a TPS voltage (would happen only at WOT, maybe
your burnout doesn't hit shift point or max throttle
angle, so you just don't see it).
But first question whether it's the RPM that's short,
or its indication (dash tachs are notoriously slow /
late).
12-24-2016, 03:53 PM
#3
Thanks for the reply. I'll agree with the dash tach-can't tell in 1st gear but definitely the 2-3 shift is short on the dash tach. Next time at the track I'll data log the run and pull any codes right after.
It has done this with both the 4l60 and 4l80 trans and the 80e had new vss/iss sensors. Did it before the swap to 4.30 gears and with the 60e so maybe more in the tune.
Just find it damn annoying that it has only happened when at the track. Welcome to the modified world, huh?!
Thanks
Adam
It has done this with both the 4l60 and 4l80 trans and the 80e had new vss/iss sensors. Did it before the swap to 4.30 gears and with the 60e so maybe more in the tune.
Just find it damn annoying that it has only happened when at the track. Welcome to the modified world, huh?!
Thanks
Adam