speedometer not working

This is very common on the 03-06 Trailblazers. The cause is the motors behind the gauges are failing, they all go out eventually. You can get it repaired here - www.drspeedometer.com and there's a DIY guide here - www.howtorepairmyinstrumentcluster.com

I looked at part supplier websites and saw a throttle position sensor connector (electrical) but no sensor. My repair instructions sow a wiring schematic for the sensor but I think it must be incorporated in the throttle housing itself (several car manufacturers incorporate the idle air control, throttle butterfly, throttle position switch ect... all in one housing with no parts available separately. Speedometer not working is not related to the TPS It is usually the Vehicle Speed Sensor (VSS).

Customer Concern: Intermittently the speedometer will drop to 0 mph. At the same time the transmission will feel like it is slipping and the AntiLock Brake System (ABS) light will turn on. A new Vehicle Speed Sensor (VSS) has been installed. Tests/Procedures: 1. At the Powertrain Control Module (PCM) locate and backprobe with an AC Voltmeter, the Purple/White wire at pin 21 and the Lt Green/Black wire at pin 20, both on the Green connector. 2. Drive to failure while monitoring the AC voltmeter. 3. If the AC voltmeter drops to 0 while the problem is occurring locate and repair either the Purple/White or the Lt Green/Black wire. Verify the connection at both the VSS and PCM connectors. 4. If the AC voltage always remains on the voltmeter verify a clean tight connection at the PCM, if OK replace the PCM. Potential Causes: Powertrain Control Module (PCM) Vehicle Speed Sensor (VSS) Vehicle Speed Sensor (VSS) Circuit Vehicle Speed Sensor (VSS) Connector