1Z Speed sensor: no voltage

[4thdiesel]

My speedo went dead on the drive home last week. I replaced the VSS sensor in the transmission without any effort to diagnose the problem. That was easy but did not fix the issue and now I own 2 perfectly good VSS.
I then opened a wiring diagram from G60ING's signature (thanks for that) and am trying to troubleshoot. The pic below is 2 snapshots of the diagram pasted together.
The problem is this: with the ignition on, I am only getting ~ 3VDC on pin 1 of the sensor connector; it should be 14.5VDC. I traced this back to the 24 pin connector T24/9 on the engine and measure ~3VDC there as well. It actually measures ~5VDC but drops to 3 quickly. The schematic shows this black wire going to connection F25 (track 51) and looks like a dead end. This is where I get confused.
Can anyone point me in the right direction? I'm looking for the voltage source for this black wire/VSS sensor. Thanks! In the mean time...I have my head under the dash.

 

[Alchemist]

From the F25 splice inside the wiring harness, follow the blue/red wire to the relay panel. There it connects to relay J317, which is the infamous 109 relay that supplies power to all the sensors, and the ECU. Start by replacing the relay. It should be good then.

Paul

 

[4thdiesel]

Great, thanks! If it is relay 109, would I expect other sensors and/or ECU to also be malfunctioning? Should I be digging in to inspect splice F25? If so, do you know where that spice is? In any event, I'll replace Relay 109 first.

 

[4thdiesel]

Relay 109 was not the problem; I replaced it but made no difference.
After attempts to trace +voltage to the VSS sensor, I was unable to find the location of the problem. I inspected the entire wiring harness and it was intact with no signs of damage or wear. So, instead of tearing the harness apart, I opted to pull +voltage off the back-up light switch and run it over to the VSS sensor. This fixed the problem and I have not had issues since. I lost 1000 miles on the odometer during troubleshooting, but now everything is working fine.

 

[GTiTDi]

Relay 109 was not the problem; I replaced it but made no difference.
After attempts to trace +voltage to the VSS sensor, I was unable to find the location of the problem. I inspected the entire wiring harness and it was intact with no signs of damage or wear. So, instead of tearing the harness apart, I opted to pull +voltage off the back-up light switch and run it over to the VSS sensor. This fixed the problem and I have not had issues since. I lost 1000 miles on the odometer during troubleshooting, but now everything is working fine.

There is undoubtedly a damaged wire somewhere in the harness...these wiring harnesses are not known for their durability..thin wires and poor insulation leads to chafing and breaks that end up as opens or shorts...nice fix by jumping power btw