speedometer wont register
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6th Gear
Joined: Jan 2010
Posts: 6
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speedometer wont register
So I installed a new amp into the C5 and now the speedometer is pegged at 200. I also powder coated the rims so they were removed for a while. WTF?! any help would be appreciated.
Tech Contributor
Joined: Jan 2007
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From: Dyer, IN
Tech Contributor
Joined: Jan 2007
Posts: 19,350
Likes: 1,124
From: Dyer, IN
Thread Starter
6th Gear
Joined: Jan 2010
Posts: 6
Likes: 0
Tech Contributor
Joined: Jan 2007
Posts: 19,350
Likes: 1,124
From: Dyer, IN
Thread Starter
6th Gear
Joined: Jan 2010
Posts: 6
Likes: 0
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Thread Starter
6th Gear
Joined: Jan 2010
Posts: 6
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Put the Vette on jacks this weekend and traced all screws and their exit points. No damage to the wiring. I am going to try the battery disconnection again and hope for the best. after that its off to the dealership.
Tech Contributor
Joined: Oct 1999
Posts: 41,026
Likes: 9,777
From: Charlotte, NC (formerly Endicott, NY)
Sounds like you did something to the Instrument Panel Speedometer circuit. The PCM sends a pulse train to the IP speedo circuit which then provides a voltage for the analog speedo needle and a digital signal that is sent to the HUD. If the HUD is working that means the PCM is getting the signal from the Vehicle Speed Sensor and is transmitting it to the IP Speedo circuitry and the Speedo Circuitry is sending a signal to the HUD. That leaves the analog needle as the only thing not working. Could be a voltage surge from the amp installation fried the output circuit for the needle.
Here is the official theory of operation for the speedo circuits from the Service Manual:
Instrument Panel Speedometer
The IPC displays the vehicle speed based on the information from the vehicle speed sensor. The PCM converts the data from the vehicle speed sensor to a 4000 pulses/mile signal. The IPC uses the vehicle speed signal circuit (4000 pulses/mile) from the PCM in order to calculate the vehicle speed. The speedometer defaults to 0 km/h (0 mph) if a malfunction in the vehicle speed signal circuit (4000 pulses/mile) exists. The speedometer displays either miles or kilometers as requested by the activation of the English/metric button on the driver information center (DIC). The associated indicator (MPH or KM/H) illuminates.
HUD Speedometer
The HUD receives a signal from the IPC indicating vehicle speed in either English (mph) or metric (km/h) units.
Bill
Here is the official theory of operation for the speedo circuits from the Service Manual:
Instrument Panel Speedometer
The IPC displays the vehicle speed based on the information from the vehicle speed sensor. The PCM converts the data from the vehicle speed sensor to a 4000 pulses/mile signal. The IPC uses the vehicle speed signal circuit (4000 pulses/mile) from the PCM in order to calculate the vehicle speed. The speedometer defaults to 0 km/h (0 mph) if a malfunction in the vehicle speed signal circuit (4000 pulses/mile) exists. The speedometer displays either miles or kilometers as requested by the activation of the English/metric button on the driver information center (DIC). The associated indicator (MPH or KM/H) illuminates.
HUD Speedometer
The HUD receives a signal from the IPC indicating vehicle speed in either English (mph) or metric (km/h) units.
Bill
Le Mans Master
Joined: Sep 2003
Posts: 6,272
Likes: 225
From: Farmington CT
Cruise-In VII Veteran
bud, just lay down and shoot a flashlight on top of the diff, the harness runs ON TOP of the diff
you will see a nice wood screw that is shredded through the harness
I am just speculating of course
you will see a nice wood screw that is shredded through the harness
I am just speculating of course
Tech Contributor
Joined: Oct 1999
Posts: 41,026
Likes: 9,777
From: Charlotte, NC (formerly Endicott, NY)
Bill
Thread Starter
6th Gear
Joined: Jan 2010
Posts: 6
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Update
Thank you everyone who posted solutions and data for my problem.
Your never going to believe this one.
Driving back from town app. 50 miles, I was traveling down the road when the speedo suddenly clicked on and started working perfect...All by itself. After turning the car on and off a few times (after I stopped) all gauges reset as they should. I am pleased that the speedo is working again and that I did no damage to it but I am so mind boggled to what had happened.
Thanks again everyone your suggestions were great.
Your never going to believe this one.
Driving back from town app. 50 miles, I was traveling down the road when the speedo suddenly clicked on and started working perfect...All by itself. After turning the car on and off a few times (after I stopped) all gauges reset as they should. I am pleased that the speedo is working again and that I did no damage to it but I am so mind boggled to what had happened.
Thanks again everyone your suggestions were great.
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Sounds like you did something to the Instrument Panel Speedometer circuit. The PCM sends a pulse train to the IP speedo circuit which then provides a voltage for the analog speedo needle and a digital signal that is sent to the HUD. If the HUD is working that means the PCM is getting the signal from the Vehicle Speed Sensor and is transmitting it to the IP Speedo circuitry and the Speedo Circuitry is sending a signal to the HUD. That leaves the analog needle as the only thing not working. Could be a voltage surge from the amp installation fried the output circuit for the needle.
Here is the official theory of operation for the speedo circuits from the Service Manual:
Instrument Panel Speedometer
The IPC displays the vehicle speed based on the information from the vehicle speed sensor. The PCM converts the data from the vehicle speed sensor to a 4000 pulses/mile signal. The IPC uses the vehicle speed signal circuit (4000 pulses/mile) from the PCM in order to calculate the vehicle speed. The speedometer defaults to 0 km/h (0 mph) if a malfunction in the vehicle speed signal circuit (4000 pulses/mile) exists. The speedometer displays either miles or kilometers as requested by the activation of the English/metric button on the driver information center (DIC). The associated indicator (MPH or KM/H) illuminates.
HUD Speedometer
The HUD receives a signal from the IPC indicating vehicle speed in either English (mph) or metric (km/h) units.
Bill
Here is the official theory of operation for the speedo circuits from the Service Manual:
Instrument Panel Speedometer
The IPC displays the vehicle speed based on the information from the vehicle speed sensor. The PCM converts the data from the vehicle speed sensor to a 4000 pulses/mile signal. The IPC uses the vehicle speed signal circuit (4000 pulses/mile) from the PCM in order to calculate the vehicle speed. The speedometer defaults to 0 km/h (0 mph) if a malfunction in the vehicle speed signal circuit (4000 pulses/mile) exists. The speedometer displays either miles or kilometers as requested by the activation of the English/metric button on the driver information center (DIC). The associated indicator (MPH or KM/H) illuminates.
HUD Speedometer
The HUD receives a signal from the IPC indicating vehicle speed in either English (mph) or metric (km/h) units.
Bill
I had a DVD/NAV installed. The installer did not know where the VSS was, so I asked somebody with a service manual to look it up and found it. Once I tapped into the wire coming from the PCM, my NAV started working and I can see the speed on the NAV unit in mph.
This was years ago. But now I notice that when I am decelerating the speedo needle will drop to 0 mph once I get below 40 mph. When I accelerate from 0 mph it will not register until above 35 mph. I thought maybe the VSS was bad, but I noticed that the GPS/NAV MPH is still working fine from 0-40 mph. So since it takes it's reference from the VSS the VSS must still be OK...or is it the analog needle in the Speedo?
It really reminds me of the when the old mechanical speedos would start to go out and they begin bouncing up and down. But I know there is nothing mechanical driving the speeds in the C5.
Tech Contributor
Joined: Oct 1999
Posts: 41,026
Likes: 9,777
From: Charlotte, NC (formerly Endicott, NY)
I think this may have helped me lol, but I have another question.
I had a DVD/NAV installed. The installer did not know where the VSS was, so I asked somebody with a service manual to look it up and found it. Once I tapped into the wire coming from the PCM, my NAV started working and I can see the speed on the NAV unit in mph.
This was years ago. But now I notice that when I am decelerating the speedo needle will drop to 0 mph once I get below 40 mph. When I accelerate from 0 mph it will not register until above 35 mph. I thought maybe the VSS was bad, but I noticed that the GPS/NAV MPH is still working fine from 0-40 mph. So since it takes it's reference from the VSS the VSS must still be OK...or is it the analog needle in the Speedo?
It really reminds me of the when the old mechanical speedos would start to go out and they begin bouncing up and down. But I know there is nothing mechanical driving the speeds in the C5.
I had a DVD/NAV installed. The installer did not know where the VSS was, so I asked somebody with a service manual to look it up and found it. Once I tapped into the wire coming from the PCM, my NAV started working and I can see the speed on the NAV unit in mph.
This was years ago. But now I notice that when I am decelerating the speedo needle will drop to 0 mph once I get below 40 mph. When I accelerate from 0 mph it will not register until above 35 mph. I thought maybe the VSS was bad, but I noticed that the GPS/NAV MPH is still working fine from 0-40 mph. So since it takes it's reference from the VSS the VSS must still be OK...or is it the analog needle in the Speedo?
It really reminds me of the when the old mechanical speedos would start to go out and they begin bouncing up and down. But I know there is nothing mechanical driving the speeds in the C5.
Bill
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Does the speedometer read the correct speed once it gets off 0? As the description I posted above indicates the speedo will register 0 if it senses something wrong in the circuit from the PCM. Is the NAV unit getting its signal from the PCM or directly from the VSS before it goes to the PCM? Your speedo could be taking a crap or the signal it is receiving may be getting weak or noisy from the load the NAV unit is putting on the PCM if it is getting its signal from the PCM. If not the PCM may not be sending a good signal. If you have a HUD what is it doing? Do you have any codes registering when you read the codes using the DIC?
Bill
Bill
Yes once the speedo registers above 30 mph either accelerating or decelerating...it reads correct...and matches what is on the NAV mph.
I tapped into the VSS at the wire as it comes out of the PCM on the way to the speedo.
No codes.
Le Mans Master
Joined: Sep 2000
Posts: 6,976
Likes: 527
From: Clouds Over California
Does the speedometer read the correct speed once it gets off 0? As the description I posted above indicates the speedo will register 0 if it senses something wrong in the circuit from the PCM. Is the NAV unit getting its signal from the PCM or directly from the VSS before it goes to the PCM? Your speedo could be taking a crap or the signal it is receiving may be getting weak or noisy from the load the NAV unit is putting on the PCM if it is getting its signal from the PCM. If not the PCM may not be sending a good signal. If you have a HUD what is it doing? Do you have any codes registering when you read the codes using the DIC?
Bill
Bill
Previously I was keeping the NAV unit turned off to troubleshoot whether it was interefering with the signal to the Speedo. But this weekend I pulled the wheel well panel off to the PCM and disconnected the wire from the NAV unit that I used to tap into the VSS on the PCM harness. My speedo now works fine.
Now to get my NAV unit back online. I had it hooked up to the VSS wire at the connnector, I am not sure (can't remember) if the wire on the PCM connector is the one between the VSS and the PCM or between the PCM and Speedo??
Any recommendations on this? I have a separate post on the C5 Tech section if you want to respond to that.
Thanks
