89 chev 1500 erratic speedometer


Old 02-11-10, 07:53 AM
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89 chev 1500 erratic speedometer

Odometer is erratic. Looking for the speed buffer to check connections. Speed sensor was just replaced but problem still exists.
Hayes manual has nice wiring diagram, but does not disclose where the units are physically located on the vehicle.
The symbol on the wiring diagram seems to indicate the odometer movement is a voltage driven meter with a spring return to zero mph.
Is it legal for an owner to replace the odometer if it is in fact at fault?
Any ideas as to what the problem is? Tom
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Old 02-11-10, 11:56 AM
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I think you may have your terms mixed up, the odometer records the miles traveled,the spedo indicates the speed you are traveling. Lets start from there to describe your symptoms.
Old 02-12-10, 03:50 PM
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If you have enough information about which wires/signals are which from your Haynes wiring diagrams, then measure the signals to the instrument cluster with a multimeter set on AC volts.

You should see an increase in voltage as you increase your speed. This would give you a ballpark idea that the signal was ok if it was consistent and the speedometer was doing something different. Indicate a problem with the instrument cluster (which is a common problem for GM vehicles).

Another test is if you have cruise control. If this works, then this also indicates the "speed signal" (VSS) is working.

As to replacing the instrument cluster/speedometer/odometer. Check your state laws. I think my state says you must put a label on the instrument cluster noting the difference. Or if the vehicle is over 10 years old, you don't need to do this. But these laws are probably different in each state as are many things! Check with your DMV.

If you need information as to where specific electrical things are located, a factory service manual set would have complete electrical diagrams and locations of everything in the vehicle. These 4 book sets can be a total of 2000 pages long! Order from dealer of helminc.com

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