Speedometer/ABS issue

I have a 2008 Silverado 1500 WT with the V-6. It has approximately 161000 miles. I don’t drive it much, only put about 30000 on it in the last 3 years that I have owned it. Last month, I noticed the ABS light on during a trip to town. The following day, it went out. Two days ago, I was using my truck on a job and was sitting parked with the engine idling. The ABS light came on again and the warning chyme also sounded. While looking at the instrument panel, I noticed that while sitting with the transmission in park idling, the speedometer would bounce sporadically from 0-10mph. Can I assume that the two are related issues and if so, where do I start looking? Thanks in advance.

Start by getting the DTC’s read especially those for the ABS. Otherwise you will probably be guessing at causes and parts until the cows come home…

They are not related. Speed comes from a sensor in the transmission. ABS sensors are at each wheel. You need a scanner to view the data from the sensors and the error codes.

So I plugged my scanner in and no codes were found in the DTC or anywhere else. Ran an errand to town. As I was backing out of the driveway, the ABS light goes out. I have no clue. Curiously enough, same time I was having problems with the ABS light/Speedometer fiasco, my drivers side headlight went out and as I was driving came back on some 2 minutes later. I am wondering if I may have a grounding issue somewhere.

I would think not related, and a failing stepper motor for the speedo.

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The transmission shifting problem and the speedometer malfunction might be caused by a failing transmission output speed sensor. The ABS computer may have detected a correlation problem between the PCM vehicle speed and the rear wheel speed sensor input and illuminated the ABS warning light.

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Your DTC scanner doesn’t read Abs codes. If it can take real time data, see if it can read the speed. If it can, your stepper motor in the dash is dead.

just to rule it out make sure your brake fluid is not low. that can cause the brake ABS
light to go on and off. especially if the fluid is on the borderline of being low.

Brake fluid level was fine. Speedometer working fine now and no more ABS light. Not sure what’s going on.