Help ! C5 Speedometer not registering MPH !
Thread Starter
Intermediate
Joined: Feb 2013
Posts: 34
Likes: 1
From: Norwich Norfolk
Help ! C5 Speedometer not registering MPH !
Hi, I'm new to this forum but have been around Corvettes for around 15 years. I wonder if you chaps could help me.
I bought a European spec '99 coupe manual last week and I have a couple of problems with it.
The first is the speedo, it cycles on start up, all the gauges work fine apart from the the speedo on the move. the only fault code I am getting is 38 RTD C1743 H C = Loss of vehicle speed signal to the real time damping.
The Vehicle speed sensor is working, I tested it by first using the cruise to obtain a speed reading(worked) and also the reverse lockout was operational. I pulled the VSS plug and the cruise didn't work and reverse was obtainable at speed.
Has anyone had this and cured it ??
The other thing that's confusing me is this;
On the RPO sticker in the glove box it states the car has RPO T82 = Twilight sentinel. The lights weren't coming on auto so I went into Options and there is NO option for Twilight control ! Could this anomally be connected to the speedo problem ?
I would be very grateful if you have any solutions !
I bought a European spec '99 coupe manual last week and I have a couple of problems with it.
The first is the speedo, it cycles on start up, all the gauges work fine apart from the the speedo on the move. the only fault code I am getting is 38 RTD C1743 H C = Loss of vehicle speed signal to the real time damping.
The Vehicle speed sensor is working, I tested it by first using the cruise to obtain a speed reading(worked) and also the reverse lockout was operational. I pulled the VSS plug and the cruise didn't work and reverse was obtainable at speed.
Has anyone had this and cured it ??
The other thing that's confusing me is this;
On the RPO sticker in the glove box it states the car has RPO T82 = Twilight sentinel. The lights weren't coming on auto so I went into Options and there is NO option for Twilight control ! Could this anomally be connected to the speedo problem ?
I would be very grateful if you have any solutions !
Le Mans Master
Joined: Mar 2011
Posts: 6,835
Likes: 301
From: Columbia SC
Do you have HUD, and if so do you get MPH there? If no one here can help from experience I can look in my factory manual and see if there are any diagnostics on this. Have you looked to see if there are any codes showing up? If so you need to post what they are. If you don't know how to do that let us know.
Thread Starter
Intermediate
Joined: Feb 2013
Posts: 34
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From: Norwich Norfolk
HI , Thanks for the reply, yes I have HUD and it displays everything including MPH but the MPH remains at zero on the move.
After clearing all the codes then going for a drive, the only code that is thrown is 38RTD C1743 H C = Loss of vehicle speed signal to the real time damping.
It seems to me that, apart from me, the only thing that is worried about the fault is the Real Time Damping.
I wondered if it could be a ground problem, one thing that might be relevant, the car was stored for about 8 months previous to me buying it, it killed the battery dead, so the previous owner put a new battery on last week.
After clearing all the codes then going for a drive, the only code that is thrown is 38RTD C1743 H C = Loss of vehicle speed signal to the real time damping.
It seems to me that, apart from me, the only thing that is worried about the fault is the Real Time Damping.
I wondered if it could be a ground problem, one thing that might be relevant, the car was stored for about 8 months previous to me buying it, it killed the battery dead, so the previous owner put a new battery on last week.
Le Mans Master
Joined: Mar 2011
Posts: 6,835
Likes: 301
From: Columbia SC
Just to clarify, are you saying both the dash gauge and the HUD do NOT show RPM once you start driving? Once I get your feedback I will look at the FSM and get back to you. Sounds like it may be something in the wiring/connector downstream somewhere.
Le Mans Master
Joined: Mar 2011
Posts: 6,835
Likes: 301
From: Columbia SC
I am looking into my mauals. I have found out the VSS sends a signal to the BCM (don't know what for yet, may be cruise control?) and to the PCM. The PCM determines the speed and sends it to the IPC, instrument panel cluster. I will keep researching my manual.
PS: Sometimes disconnecting the battery temporarily can reslove some issues. Try it while I look some more.
PS: Sometimes disconnecting the battery temporarily can reslove some issues. Try it while I look some more.
Le Mans Master
Joined: Sep 2003
Posts: 6,262
Likes: 222
From: Farmington CT
Cruise-In VII Veteran
can you clear the RTD and maintain the cruise control setting while getting another "C" code in the RTD system?
for others reading the VSS signal to speedo is picked up on the diff(top of diff has the VSS).
for others reading the VSS signal to speedo is picked up on the diff(top of diff has the VSS).
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Thread Starter
Intermediate
Joined: Feb 2013
Posts: 34
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From: Norwich Norfolk
Yes, I can clear the code, when I take the car out the codes reappears, I am getting a speed reading from the cruise on the DIC , I can increase or decrease the speed using the criuse and the reverse lock out works.
Thread Starter
Intermediate
Joined: Feb 2013
Posts: 34
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From: Norwich Norfolk
Well I disconnected the battery left it 10 minutes and reconnected, reset the RTD code and went for a ride, the RTD code is back but Historical only. Speedometer still not functioning 
Le Mans Master
Joined: Mar 2011
Posts: 6,835
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From: Columbia SC
Here is the schematic related to VSS and suspension control:
It could be a connection in the circuit. I can't find anywhere in the manual where your code shows up (yet). I am not giving up with the manual search to find everything the VSS feeds and interacts with. Why don't you post a request specifically on where to find the diagnostics on this code? I hope it is not a PCM issue.
It could be a connection in the circuit. I can't find anywhere in the manual where your code shows up (yet). I am not giving up with the manual search to find everything the VSS feeds and interacts with. Why don't you post a request specifically on where to find the diagnostics on this code? I hope it is not a PCM issue.
Le Mans Master
Joined: Mar 2011
Posts: 6,835
Likes: 301
From: Columbia SC
Assuming the RTD issue is gone (hope, hope) I will focus on input and output from the PCM. May want to pull the PCM connection and check it and replace it and see if that helps. I will not give on you, I like learning about the design so long as my brain does not explode.
I hope we don't have to go to connections in the dash.
I hope we don't have to go to connections in the dash.
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
Well, that schematic helps. I couldn't look anything up until tonight.
That ESC controller is the real-time damping and it's where the code is coming from. So, the PCM output isn't reaching the dash or the ESC controller.
Troubleshooting it could be a pain. It's a pulsed output so a simple meter won't be too much help to measure for an output. First step is pull the PCM connector and check the pin/connection as well as for measure the wire to ground to see if it's shorted to ground in the wiring harness. Next 's to pull the ESC connector end and check if the wire has a break in it.
Another thing. Take a look at the harnesses below the battery. It's possible the battery has leaked acid on the harness and you have some damaged wiring you have to fix.
That ESC controller is the real-time damping and it's where the code is coming from. So, the PCM output isn't reaching the dash or the ESC controller.
Troubleshooting it could be a pain. It's a pulsed output so a simple meter won't be too much help to measure for an output. First step is pull the PCM connector and check the pin/connection as well as for measure the wire to ground to see if it's shorted to ground in the wiring harness. Next 's to pull the ESC connector end and check if the wire has a break in it.
Another thing. Take a look at the harnesses below the battery. It's possible the battery has leaked acid on the harness and you have some damaged wiring you have to fix.
Thread Starter
Intermediate
Joined: Feb 2013
Posts: 34
Likes: 1
From: Norwich Norfolk
Well, that schematic helps. I couldn't look anything up until tonight.
That ESC controller is the real-time damping and it's where the code is coming from. So, the PCM output isn't reaching the dash or the ESC controller.
Troubleshooting it could be a pain. It's a pulsed output so a simple meter won't be too much help to measure for an output. First step is pull the PCM connector and check the pin/connection as well as for measure the wire to ground to see if it's shorted to ground in the wiring harness. Next 's to pull the ESC connector end and check if the wire has a break in it.
Another thing. Take a look at the harnesses below the battery. It's possible the battery has leaked acid on the harness and you have some damaged wiring you have to fix.
That ESC controller is the real-time damping and it's where the code is coming from. So, the PCM output isn't reaching the dash or the ESC controller.
Troubleshooting it could be a pain. It's a pulsed output so a simple meter won't be too much help to measure for an output. First step is pull the PCM connector and check the pin/connection as well as for measure the wire to ground to see if it's shorted to ground in the wiring harness. Next 's to pull the ESC connector end and check if the wire has a break in it.
Another thing. Take a look at the harnesses below the battery. It's possible the battery has leaked acid on the harness and you have some damaged wiring you have to fix.
I hope it's not a leaking battery problem, I have heard it can be a nightmare to fix ?? Thanks again guys
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
The PCM is buried in front of the firewall in the passenger side under the battery. If you jack the car up and remove the front passenger wheel there is a panel below you can remove to get to the PCM.
The ESC controller should be in one of the rear storage compartments. I think it's the drivers side one.
The ESC controller should be in one of the rear storage compartments. I think it's the drivers side one.
Thread Starter
Intermediate
Joined: Feb 2013
Posts: 34
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From: Norwich Norfolk
OK, I have trawled the web and found the answers to my location questions, regarding the PCM, I wish I hadn't !
Anyway, tomorrows job is to get behind that panel and see if the dreaded battery acid situation has occurred, fingers crossed it hasn't !
I'll keep you posted.
Anyway, tomorrows job is to get behind that panel and see if the dreaded battery acid situation has occurred, fingers crossed it hasn't !
I'll keep you posted.
Thread Starter
Intermediate
Joined: Feb 2013
Posts: 34
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From: Norwich Norfolk
Well I took the panel off, removed the PCM and it looks like it may the problem. There was a lot of corrosion ( it was actuallly corroded into the bracket) The Plugs are fine, no ingress evident past the seals.
The reasons I think it is shot are twofold, one, the gap between the lid and the unit where it folds around the main body was so corroded with a white substance that it was splayed away from the main body and severely pitted. Also when I tipped it over and moved it around it sounded like it was full of loose particles !
I cleaned up all the mating surfaces and put it back on, guess what ? Still no speedo !
I have come to the conclusion I need to replace it, I have found a company called Flashmasters on US Ebay who will programme a salvaged unit using my VIN.
Anybody heard of this company, any feedback on here, or can you reccommend an alternative ?
The reasons I think it is shot are twofold, one, the gap between the lid and the unit where it folds around the main body was so corroded with a white substance that it was splayed away from the main body and severely pitted. Also when I tipped it over and moved it around it sounded like it was full of loose particles !
I cleaned up all the mating surfaces and put it back on, guess what ? Still no speedo !
I have come to the conclusion I need to replace it, I have found a company called Flashmasters on US Ebay who will programme a salvaged unit using my VIN.
Anybody heard of this company, any feedback on here, or can you reccommend an alternative ?
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
You're meaning the 2 halves of the PCM were so corroded that the case has an opening in it? Sounds like it does need replacement.
Did you pull the case apart and look inside? At this point, it sounds like there is nothing to lose.
Did you pull the case apart and look inside? At this point, it sounds like there is nothing to lose.