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There is white wire coming out of the computer that you can get the signal from.
The one on your Scan tool will always work as long as there is a cam and crank trigger signal.
I would check that one wire for a direct connection from the instrument cluster to the computer itself. If that is good, then it is your ipc cluster motor.
So in order for the scan tool to correctly work, I must have both the cam and crank signals, Right?
I didn't know if the gauge cluster and the scan tool shared the same signal, because if they did it meant something was wrong in the cluster. But I will pull the computer and look at the #10 pin on red connector and check the wire as it goes through the firewall.
There is white wire coming out of the computer that you can get the signal from.
The one on your Scan tool will always work as long as there is a cam and crank trigger signal.
I would check that one wire for a direct connection from the instrument cluster to the computer itself. If that is good, then it is your ipc cluster motor.
I have 2 different wiring diagrams and they say tach signal comes from serial data bus, (gray wire coming from splice pack).
The white wire goes to antilock module.
This system is quite complicated the ECM interprets the engine speed using the Crank position sensor and Camshaft position sensor then sends it out of pin 10 White wire (C2 ECM Red connector) through the fire wall behind the ECM to C105 and then to the ECBM for brake controlling. From there (somehow) it is combined into the Serial data code of the OBD2 maybe in the (ECBM) system and then seems to be re - interpreted back out by a Serial data connection to a module inside of the instrument cluster that feeds most of the major gauges temp speedo etc... Not sure why GM thought this needed to be so complicated, but it could any of those causing the issue. I guess they just thought it was cool to add all the gauge signals into Serial data. I am sure you don't even have the car anymore, but this may help someone else.
Seems as though the OBD signal changes into different types of signals at something called a Star connector. Star Connector pin ( L ) Circuit 1036 is the serial data sent to the Gauge cluster module. All of the circuits on the Star Connector are fed by the main PPL purple Serial circuit.
Last edited by threfoldcord; Jun 8, 2024 at 03:15 PM.
Reason: add information
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Tach Signal 
F body Tachometer 
