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4L80E Erratic Shift, Speedo Bounce, ABS Light On



'96 C3500 454 2WD with 4L80E.

Intermittent problem with trans/speedo. Speedo starts bouncing at about 40mph and trans shifts up and down.

Had a similar problem 18 months ago due to low voltage at trans fuse. Replaced the ignition switch and problem solved. This time voltage was normal but replaced the ignition switch again anyway. Didn't help.

Then replaced input/output sensors and throttle position sensor. No change. Checked VSS ground at manifold.

Over the past few weeks problem has gone from very intermittent (every few days) to somewhat regular. ABS light is on, checked wheel sensors and they are good.


Don't want to detonate my trans. What should I look for next?


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3 answers to this question

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Scan it for codes !!!!!!!!!!


Stop guessing !!!!!!

You are right, that's what I should have done to begin with.

It would cost me $100. for a Tech 2 scan.

So being Scrooge McDuck I thought mathematical probability was that replacing a couple of parts would be likely to fix the problem (and was cheaper).

Anyway it appears there is a perfect correlation between wet roads and the trans issue.

On dry roads, no problem at all.

Drive it in the rain, and it acts up.

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