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VSS affecting ABS ...?

hello all,

vehicle -- 1998 S10 4x4 automatic trans.

I was driving along at about 50 mph when the speedo went to zero. About 3 seconds after that, the ABS light came on. Another 3 seconds after that, the trans. kicks down to first gear...

I made an about-face, and headed home. About 20 miles later, the SES light came on.

when I got home, the code came back as the Vehicle Speed Sensor. supposedly, the cascade of events is that : once the computer saw "zero" as the speed, but the ABS wheel speed sensor saw 50 mph, it decided that the discrepancy meant the ABS was out. *then*, the computer put the truck into "limp home" mode, restricting the speed (since it thought I had no brakes) by only giving me first gear.

I changed out the VSS, and the speedo works fine, the truck has all 4 gears back, and the brakes work fine. The SES light is out, but the ABS light comes on as soon as I start rolling.

does the ABS have it's own, separate/independent computer ? and if so, am I experiencing a leftover code ? can I clear it by disconnecting the battery overnight ?

any comments appreciated...

Reply to
myancov
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None of that sounds right to me. If the ABS was in error, it would disable it. The ABS controller is typically separate from the PCM and relies on it's own wheel speed sensors and not the VSS. Not sure about the trucks though. Do they use the VSS for rear wheel speed reference?

I haven't heard of a "limp" mode where the trans is stuck in 1st. This would likely be a result of the PCM detecting a VSS fault. Limps modes are usually related to engine performance.

With all those things happening at once, first thing I would do is have the battery tested. Check the battery connections while you're there.

Steve

Reply to
Steve Mackie

Reply to
Shep

Long time no see! He should still have his battery checked. ;)

Reply to
Steve Mackie

I think so (the factory service manual is severely lacking in explaining how to diagnose this), the VSS was on the tail of the tranny, so I reckon the driveshaft revolutions equate to rear wheel speed...

will do -- I'll report back.

Reply to
myancov

I got everything checked... the only thing that comes back is that the ABS unit itself is bad.

I find this hard to believe, since it would be a monumental coincidence that the ABS unit went bad at the same time my VSS went bad.

screw it, I don't need ABS anyhow, the truck runs/stops fine... just wish I could knock out the ABS light in the cluster !

Reply to
Pouta

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