Wiring diagram of 2000 trailblazer speedometer

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Stuck relay, short to ground in DRL wiring, bad BCM, or bad ambient light sensor,

Haynes actually have a pretty good schematic in the section labeled Body Electric. If that is confusing to you, take your time, you'll understand it when you see it in front of you. good luck, and Thank Yo for using FixYa.com for help! GO HERE:
www.fixya.com/f/landing/tagspage/blazer_wiring_diagrams?cmpid=20140714&gclid=CInSyvGq7cACFUoS7AodfW4AWQ

This one has me stumped, but what I would do is go to a junk yard( used car parts) and get a dash board panel. Sounds to me like there is a crack or short in the panel. If this doesn't help email me @ [email protected] with more info and I will go online and try to solve this problem.

Your speedometer is controlled by your computer network. The vehicle speed sensor (VSS) sends a signal to the Body Control Module (BCM) which then relays the speed sensor data via the UART data lines to the Powertrain Control Module (PCM) and the Instrument Panel Cluster (IPC). To find out why your speedometer is not functioning, you must FIRST scan your ENTIRE computer network for possible fault codes. It is possible that either the VSS is defective or the BCM is not able to relay the information due to a communications fault, or the BCM is relaying the information and the IPC is unable to receive the information due to a communications fault, or the IPC itself is defective. Wiring diagrams will be of no use until you determine which parts of the network is receiving the information from the VSS and which parts are not. This will require the use of a scan tool that can not only read generic OBD fault codes, but also access and display codes and live data from the BCM, PCM and IPC.

BAD VECHICLE SPEED SENSOR WILL CAUSE THE SPEEDOMETER NOT TO WORK.CHECK SPEED SENSOR WIRE HARNESS MAKE SURE WIRE HARNESS NOT DAMAGED OR DISCONNECTED.

Are you looking for a certain sensor? What engine?

The first place to start would be removing the cluster the overhead and wiggling wires and connectors, also wiggling wires at the BCM and junction block. Checking all fuses. If you find nothing, then the most logical place to start would be the BCM, but only after all these other posibilities have been checked.

More likely is the sensor on the transmission either failed, or the wire came loose. You can check the wire by crawling under the vehicle, looking at the transmission, and you should see a sensor with a couple of wires coming off of it. Check the connector to see if it's secure. If so, it's probably the sensor. If it's loose, put it back on and check it again. Hope this helps you out.

I don't see many bad sensors I would co to an auto zone read code if its a vss ck connevtors & wires at sensor does the trns shift if not ck the purpple & green wires