Speedometer not working

JERMzSS

Well-Known Member
Technically this is on the wifes 09 ss/tc I did use my Goblin to verify that the cluster is still good lol. I swapped them and it works in my car.

Everything in the cluster works except the speedometer. It even reacts to the key coming on (centers to 0mph) but it will not move when driving.

Here's where I'm lost. I checked and through my torque app and obd2 reader it's reading the speed but it's just not reaching the cluster so I'm officially past my diagnosing skills lol.

Thanks for any help in advance.
 

Ross

Goblin Guru
So does your Goblin cluster work in the tc Cobalt? If it doesn't the issue is probably in the wiring... after the sensor, after the ODB2 port gets the signal, but before the cluster. Just shooting from the hip here, not actual working knowledge...
 

JERMzSS

Well-Known Member
I didn't try that but i will. Im guessing
the wiring goes sensor, obd2 port then the cluster??
 

Briann1177

Goblin Guru
The thing is that there is no dedicated speed sensor wiring that goes to your gauge cluster. I have the same model donor so I pulled up the pin out for the gauge cluster connector, and nothing. The only wire that makes sense as far as where your speed signal comes from would be the dark green low speed GMLAN wire. If all your other indicator lights work, then I would think that your GMLAN connection is good.

Makes zero sense.
 

JERMzSS

Well-Known Member
The thing is that there is no dedicated speed sensor wiring that goes to your gauge cluster. I have the same model donor so I pulled up the pin out for the gauge cluster connector, and nothing. The only wire that makes sense as far as where your speed signal comes from would be the dark green low speed GMLAN wire. If all your other indicator lights work, then I would think that your GMLAN connection is good.

Makes zero sense.
I used a volt meter on that wire. I got a reading but it was strange and not what I expected. . I'll see if I can get the excact reading and post them in a bit. Thanks for the replies so far.
 

ctuinstra

Goblin Guru
I used a volt meter on that wire. I got a reading but it was strange and not what I expected. . I'll see if I can get the excact reading and post them in a bit. Thanks for the replies so far.
The GMLAN is a data wire. Voltage readings will tell you nothing. An oscilloscope will show you data on the wire but that would be about it. Be careful what you put on those wires, they go directly to the "brain".

All the green wires should be tied together in this area. The DLC (OBDII) and the dash get the exact same thing. Others have cut the large black splice out and tied in the wrong green wires. You might want to ohm out the green wire to the dash down to the DLC. It should be 0 ohms.


7629
 

JSATX

Goblin Guru
Rpm, water temp, speed etc all come in on the same wire, then the instrument cluster sorts it out and displays it. If you get RPM but not speed, it’s gotta be in the cluster. But I know you said you swapped it out and it worked so that’s super confusing.
 

JERMzSS

Well-Known Member
I'm gona trybtge goblins in the car to see what it does. Has me wondering if there's an issue with the plug or one of the pins.
 

JERMzSS

Well-Known Member
The GMLAN is a data wire. Voltage readings will tell you nothing. An oscilloscope will show you data on the wire but that would be about it. Be careful what you put on those wires, they go directly to the "brain".

All the green wires should be tied together in this area. The DLC (OBDII) and the dash get the exact same thing. Others have cut the large black splice out and tied in the wrong green wires. You might want to ohm out the green wire to the dash down to the DLC. It should be 0 ohms.


View attachment 7629
Great info thanks!
 

Astraeus

Member
Did you ever figure this out? I have RPM, lights etc., but no speed or water temp.
Just fixed this on mine. The engine coolant and speed sensor plugs and both 2 pin and fairly close to each other. I had them swapped. You need to reset the ECU for it to be able to read engine temp again if anyone else has this problem. Makes an enormous power difference too...
 

JERMzSS

Well-Known Member
Just fixed this on mine. The engine coolant and speed sensor plugs and both 2 pin and fairly close to each other. I had them swapped. You need to reset the ECU for it to be able to read engine temp again if anyone else has this problem. Makes an enormous power difference too...
My ecm is acting crazy. Lonny is gonna loan me one to see if it's my issue. Thanks for the info I'll double check those connectors asap .
 

Torchandregdoc

Goblin Guru
Just fixed this on mine. The engine coolant and speed sensor plugs and both 2 pin and fairly close to each other. I had them swapped. You need to reset the ECU for it to be able to read engine temp again if anyone else has this problem. Makes an enormous power difference too...
I'm not even close to this part of my build, but trying to get a better understanding of these systems. When you say that you need to reset the ecu, are you saying to do that after you've corrected the plugs being switched?
 

Astraeus

Member
I'm not even close to this part of my build, but trying to get a better understanding of these systems. When you say that you need to reset the ecu, are you saying to do that after you've corrected the plugs being switched?
Yes. After I switched the plugs, the speedometer worked, but the ECT was still not reading on the gauge cluster. I pulled the negative battery cable off for a few minutes and when I reconnected it the temperature was displayed.
 

JERMzSS

Well-Known Member
Sorry I haven't done a good job by keeping you guys updated on this issue. My issue ended up being the BCM. I had to replace it with a factory unit and have it programmed to my vehicle. Apparently mine had locked itself out. After the BCM was replaced and programmed the speedometer, cruise control, daytime running lights, traction control and the stereo amp all started working.

Big thanks to Lonny and Adam for all their help. It took a lot of time to finally diagnose the problem.
 
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