Speedometer Error
Thread Starter
Instructor
Joined: Nov 2000
Posts: 122
Likes: 4
From: O'Fallon IL
Speedometer Error
This is a very unusual problem and my local Chevrolet service shop doesn’t want to look at and he hasn’t experienced the problem before. I track my car and when I reach speeds of 145 to 150 mph the speedometer will drop down to zero, the HUD does the same. Once I pass 150 mph the speedometer will come back up and run normal. Has anyone seen this problem before? The car is a 2006, Z-06.
Melting Slicks
Joined: Jan 2005
Posts: 2,326
Likes: 5
From: louisville "derby city" kentucky
i have had a similar problem at the drag strip. mine will go to zero at launch, then halfway down the track, it will start working again. talked to an engineer at the c5/c6 bash, and he told me that is the rear diff was spinning up very quickly, or spinning briefly uncontrolled when the tires were losing traction, this would happen. the vehicle speed sensor monitors the ring gear carrier. has never caused a cel light or been a problem, just is a weird quirk of the system i guess. i don't know if a good tuner can address this problem or not. good luck 
Race Director
Joined: Jan 2005
Posts: 10,924
Likes: 852
From: Daytona Beach FL
This is a very unusual problem and my local Chevrolet service shop doesn’t want to look at and he hasn’t experienced the problem before. I track my car and when I reach speeds of 145 to 150 mph the speedometer will drop down to zero, the HUD does the same. Once I pass 150 mph the speedometer will come back up and run normal. Has anyone seen this problem before? The car is a 2006, Z-06.
Bob
Tech Contributor
Joined: Oct 1999
Posts: 41,029
Likes: 9,780
From: Charlotte, NC (formerly Endicott, NY)
The problem has to be common to the HUD and the IP so that means it is in the signal to both of them, the ECM or the VSS from the tranny to the ECM. The VSS signal to the ECM is an analog wave form and could be susceptible to electrical noise. The connection is a two wire harness with a shield so if anything happened to the shield ground connection you could get some weird results. The ECM converts the VSS signal from the diff to a 4000 pulses per mile pulse train and sends that signal to the IP and the HUD so there could be a problem with the ECM output line. The signal could be flaky (not quite up to spec) and if there is sufficient electrical noise on the line at the speed you see the instruments drop to 0 the HUD and IP might not read the signal properly.
Bill
Bill
