So I noticed my HUD reading 0 mph. Then saw my gauged speedo matched. All other gauges work.

Hooked up OBDII and it still gets a speed reading. Which I assume comes from the VSS?

What could the cause of this be?

 

I don't know the cause, but it happened to me last week. I had stopped at a Staples store for 5 minutes and when it restarted it cranked real slow before it fired up and the steering almost felt like manual vs power, the speedometer stayed on zero, and the check engine light came on. I drove home, disconnected the battery, charged it for a bit, then hooked it up and everything was fine again. I wrote it off to excessive heat, since it was 117 here that day.

 

If your speedo is reading zero ... just think of all the gas your going to save !

 

Yeah, but it takes forever to get where you're going.

 

This happened to my 'O6 Z about three weeks ago. This actually happened 3 times and the first two did not show a check engine light. Finally I got the light and the code was PO335; Crankcase position indicator sensor. My friend who is a GM master mechanic verified and said it even happened to his suburban. This mechanic did warn me to get it replaced right away or I could find myself stranded somewhere. He highly recommended replacing the sensor with a genuine GM Part. To do this a person only has to take out the starter which gives access to the sensor and it's a simple replacement. Of course the most difficult part is removing the starter. To slide the starter out from below, I found the easiest way was to loosen the exhaust manifold bolts that connect to the block. In addition, I had just been experiencing a slight delay when starting my car & had been suspecting my starter's solenoid was getting tired. So while in there, I also replaced the starter with an AcDelco that I bought from NAPA. The check engine light went away within a few miles of driving and all is good. Best of luck.

 

Thanks for that info. You just saved me some time and aggravation. I had my spare starter rebuilt including a new solenoid several months ago and awaiting a cooler than 90 F day to do the swap. Looks like replacing the CKP sensor will be added to the parts list to avoid R&R the starter an additional time. That's why this forum is so great.

 

Hmm....I'm not getting any codes or check engine light. I might try the battery idea..mine is pretty old and a dying battery can cause strange problems sometimes.