98 Z71 multiple problems

MyZ70FUN · August 14, 2005

After driving home last weekend I made the exit near my home when suddenly these symptoms all happened at once wich lead me to believe it may be sensor or ECM related..

1. My Truck will no longer shift past 2nd gear. (park,neutral, 1st 2nd and reverse work) 3rd or 4th will not engauge.

2. My speedometer started dancing radically all over the place.

3. My ABS light came on. The light comes on now after I drive a few feet after leaving from park.

4. My truck automatically went into 4 wheel hi on its own. Which corrected it self when I pushed the 2 wheel hi button moments later.

A friend is bringing a scanner over later this week, any hints or helpful advice would be greatly appreciated.

Rob

GM-Tech · August 15, 2005

2. My speedometer started dancing radically all over the place.

That's the key. Trans shifting is dependant on a vehicle speed signal, as is the speedometer. The "3-sensor" type of ABS system uses the same speed signal to determine what's going on with both rear wheels.

Look for the loss of speed signal and you'll find your problem.

MyZ70FUN · August 17, 2005

Is there a simple way to find out wich sesnor is bad I just got back from auto zone and discovered that my Z71 has 5 vehicle speed sensors, two of them happen to cost 140 a piece..?? The other 3 cost around 25 bucks each.

Rob

2. My speedometer started dancing radically all over the place.

That's the key. Trans shifting is dependant on a vehicle speed signal, as is the speedometer. The "3-sensor" type of ABS system uses the same speed signal to determine what's going on with both rear wheels.

Look for the loss of speed signal and you'll find your problem.

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GM-Tech · August 17, 2005

Telling us what year truck you have would help greatly. Also, the only speed sensor that would affect the speedometer and the shifting of the trans is the VSS (vehicle speed sensor) which is in the trans or transfer case on a 4-wheel drive.

The other sensors would be wheel speed sensors, and they are not vehicle speed sensors. These would only affect the ABS and not the speedometer or the trans.

MyZ70FUN · August 17, 2005

It's a 98 Silverado z71. would the vehicle speed sensor also cause my abs light to come on?

Thanks, your help is greatly appreciated.

GM-Tech · August 17, 2005

It's a 98 Silverado z71. would the vehicle speed sensor also cause my abs light to come on?

To the best of my knowledge, you have a 3-sensor system as I previously mentioned. That is, individual wheel speed sensors for the front wheels (only) and the ABS uses the VSS for rear wheel speed.

So in this case, yes, a loss of VSS signal would cause all the things you described in your original post.

MyZ70FUN · August 21, 2005

GM TECH thanks soooooooo much for helping me with my trucks problem!!!! You were right it was one of the speed sensors located in the tail of the transmission. I bought all of the 3 sensors as you mentioned. I had a little luck on my side while installing the sensors I removed them one by one for inspection and noticed that part number s8310 wich I bought from Oreileys had a large amount of fine metal shavings around the base was going to be my first choice of replacing. After replacing only that sensor I decided to take my truck for a spin all of my problems listed above were immediatly corrected I was able to take back the other two sensors and get a refund since they hadnt been used !!!

You made my family's weekend we were bucling down to purchase a 1500 transmission and it turned up being a 66 dollar sensor !!

Thanks again !!!

It's a 98 Silverado z71. would the vehicle speed sensor also cause my abs light to come on?

To the best of my knowledge, you have a 3-sensor system as I previously mentioned. That is, individual wheel speed sensors for the front wheels (only) and the ABS uses the VSS for rear wheel speed.

So in this case, yes, a loss of VSS signal would cause all the things you described in your original post.

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GM-Tech · August 21, 2005

I'm glad to hear it was an easy fix, but just a little clarification...

"I bought all of the 3 sensors as you mentioned. "

I did not say you needed to replace one (or all) of 3 sensors! Just that the ABS is a three sensor system, i.e. the two front wheel speed sensors and then the VSS for the rear wheel speed. The front wheel speed sensors would have nothing whatsoever to do with the trans or speedometer.

Anyway, like I said, glad to hear it is fixed.