No Speedo = bad LCD panel?
Thread Starter
Burning Brakes
Joined: Feb 2000
Posts: 1,247
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From: Parker, Colorado, USofA
No Speedo = bad LCD panel?
I'm using the service manual to hunt down a problem with getting no speedo information. The Sensor is new, the wiring appears intact, and the service manual just says 'replace IP cluster'.
Has anybody run into this? I'd just as soon NOT swap the IP cluster, and am NOT against pulling it apart to fix a fault. (I've done so before.)
Has anybody run into this? I'd just as soon NOT swap the IP cluster, and am NOT against pulling it apart to fix a fault. (I've done so before.)
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Re: No Speedo = bad LCD panel? (RocketSled)
GM did not expect their technicians to repair the cluster. This was left to cluster service centers. Does the odometer work? If so, that proves that the speed sensor is sending pulses to the cluster. If the odometer works, then you could have a defective LCD, or defective circuitry that drives the LCD. You can get an LCD, and circuit info is available on http://www.batee.com, but no explanation of how the speedometer circuit works, nor a source for integrated circuits to do the repair yourself. A service center should be used if the circuit board proves defective.
Thread Starter
Burning Brakes
Joined: Feb 2000
Posts: 1,247
Likes: 2
From: Parker, Colorado, USofA
Re: No Speedo = bad LCD panel? (jfb)
The VSS sends an AC voltage based on speed. (I know this because, being stupid, I broks the old VSS housing getting it out, put the new one in to keep the tranny from hemorraging, and put the old one in a vice with a drill running it to make sure I'd swapped it out for nothing. :rolleyes: )
The service manual THEN says to run a test signal up the system and observe the speedo. I attached the 'spare' sensor and got Nada.
They then tell you to make sure one or both of the lines going into the sensor don't have a short to ground. Bingo. Purple wire has a short to ground.
THEN check at the plug under the passenger side hushpanel. Still have a short to ground.
End result of that process - Swap out the IP. (and the ODO doesn't work, btw)
All LCD panels light. All LCD panels do the initial power-on test. Since one board handles LCD display, and the other board handles logic, it's pretty obvious it's the logic board at fault. I've got corroborating evidence by calling a guy that rebuild the panels on the internet. Curiously enough, he suggested I send a note describing the problem when I send the cluster in, as the usual tests don't include checking the speedo.
It's just another $250 bill, and another week of downtime in a car that's cost me a ton of time and money...I wanna DRIVE it! :chevy
The service manual THEN says to run a test signal up the system and observe the speedo. I attached the 'spare' sensor and got Nada.
They then tell you to make sure one or both of the lines going into the sensor don't have a short to ground. Bingo. Purple wire has a short to ground.
THEN check at the plug under the passenger side hushpanel. Still have a short to ground.
End result of that process - Swap out the IP. (and the ODO doesn't work, btw)
All LCD panels light. All LCD panels do the initial power-on test. Since one board handles LCD display, and the other board handles logic, it's pretty obvious it's the logic board at fault. I've got corroborating evidence by calling a guy that rebuild the panels on the internet. Curiously enough, he suggested I send a note describing the problem when I send the cluster in, as the usual tests don't include checking the speedo.
It's just another $250 bill, and another week of downtime in a car that's cost me a ton of time and money...I wanna DRIVE it! :chevy
- 1986 Original Owner -
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Re: No Speedo = bad LCD panel? (RocketSled)
You didn't mention a Code 24. The ECM will set this code if it doesn't receive speed info from the Cluster. Other conditions must be met, but if you are driving normally, and the ECM isn't receiving speed info from the Cluster, you'll see this code pretty quickly. This is what you'll see if you drive with the Cluster out. Are you getting this code?
- 1986 Original Owner -
Joined: Apr 1999
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From: North Yorkshire, England
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Re: No Speedo = bad LCD panel? (RocketSled)
No problem, makes sense now.
