Speedometer shows 15mph when I'm not moving
Thread Starter
Burning Brakes
Joined: May 2007
Posts: 1,078
Likes: 5
From: Denver, North Carolina
Speedometer shows 15mph when I'm not moving
My speedometer is registering 15 mph when I start the car. It will go into any gear (M6) but I'm locked out of reverse. Anybody know what could be going on?
Le Mans Master
Joined: Sep 2003
Posts: 6,276
Likes: 227
From: Farmington CT
Cruise-In VII Veteran
speedo works off the speed sensor in the diff, if the car is not rolling......I would swap the cluster
uncommon for these to fail
you can swap the cluster in about 20 minutes
www.vettessentials.com
w/ the info from Aloha, I would ck the ground outback in the LHS wheel well, this ties into the trans/tunnel harness, sounds like there is a sparktrician problem here
the cluster swap is my "can bird in the hangar, 20 minute TS fix", just rules out the possibility
uncommon for these to fail
you can swap the cluster in about 20 minutes
www.vettessentials.com
w/ the info from Aloha, I would ck the ground outback in the LHS wheel well, this ties into the trans/tunnel harness, sounds like there is a sparktrician problem here
the cluster swap is my "can bird in the hangar, 20 minute TS fix", just rules out the possibility
Last edited by SteveDoten; Dec 10, 2009 at 06:16 PM.
"AlohaC5" Senior Member
Joined: Jun 2003
Posts: 3,562
Likes: 44
From: Madison, AL
Your reverse lockout may not be engaging - could be a bad blocking ring or solenoid is failing, which is located on top of the transmission. From what I understand its a relatively cheap and easy problem to fix. Are you throwing any codes? The reverse lockout will engage above 3 MPH. You may want to contact RPM Transmission for advice.
Melting Slicks
Joined: Dec 2003
Posts: 2,334
Likes: 11
From: las vegas nv.
Thread Starter
Burning Brakes
Joined: May 2007
Posts: 1,078
Likes: 5
From: Denver, North Carolina
I think the issue is less about being locked out of reverse or any type of transmission problem, that is really just a symptom. Like I said my speedo is showing that the car is moving at 15 mph while it is in fact sitting still, that's why it won't go into reverse.
So does anyone know why my speedo thinks the car is moving?
So does anyone know why my speedo thinks the car is moving?
Le Mans Master
Joined: Sep 2003
Posts: 6,276
Likes: 227
From: Farmington CT
Cruise-In VII Veteran
I think the issue is less about being locked out of reverse or any type of transmission problem, that is really just a symptom. Like I said my speedo is showing that the car is moving at 15 mph while it is in fact sitting still, that's why it won't go into reverse.
So does anyone know why my speedo thinks the car is moving?
So does anyone know why my speedo thinks the car is moving?
2. bad cluster(easy elimination if you have a C5 friend)
3. speedo gets the signal from the diff speed sensor, you can reach the plug from the rear of the car
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
The speed sensor output is an AC Signal. It can/should only generate a signal if the ring gear is moving. With that being said, if one of the wires is OPEN, it could be seeing stray voltage.
When I get home I will give you what you need to test the wiring continuity of the sensor.
Does the speedometer operate correctly (READ THE CORRECT SPEED) once the car exceeds 15 MPH?
Is the odometer working and recording the correct distance?
BC
When I get home I will give you what you need to test the wiring continuity of the sensor.
Does the speedometer operate correctly (READ THE CORRECT SPEED) once the car exceeds 15 MPH?
Is the odometer working and recording the correct distance?
BC
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Tech Contributor
Joined: Jan 2007
Posts: 19,448
Likes: 1,155
From: Dyer, IN
Is this problem something that just started, or has work been done recently on the car?
Tech Contributor
Joined: Oct 1999
Posts: 41,055
Likes: 9,817
From: Charlotte, NC (formerly Endicott, NY)
First, the reverse lock out can be over ridden. It is spring loaded and if you push hard enough you will be able to get the car into reverse. They designed it that way in case the solenoid failed and the use of reverse was required.
The VSS signal goes to the PCM and then the PCM sends a 4000 pulse per mile VSS signal to the instrument panel. The PCM activates the reverse lockout so the PCM is seeing a pulse train that indicates vehicle operation above 3 mph. The problem may reside in the VSS sensor or in the wiring from the sensor to the PCM. As Bill C indicates an open may be causing a stray signal to be generated in the wiring from the VSS sensor to the PCM.
The problem could also be in the PCM. I do not know if the VSS signal is a straight pass through the PCM or whether the PCM regenerates the signal it receives. If it regenerates the signal then the PCM could be causing the problem.
Since the speedo is reading 15 mph that should also put the car into skip shift mode. Is skip shift activating when you drive the car?
Does the DIC indicate any codes present?
Bill
The VSS signal goes to the PCM and then the PCM sends a 4000 pulse per mile VSS signal to the instrument panel. The PCM activates the reverse lockout so the PCM is seeing a pulse train that indicates vehicle operation above 3 mph. The problem may reside in the VSS sensor or in the wiring from the sensor to the PCM. As Bill C indicates an open may be causing a stray signal to be generated in the wiring from the VSS sensor to the PCM.
The problem could also be in the PCM. I do not know if the VSS signal is a straight pass through the PCM or whether the PCM regenerates the signal it receives. If it regenerates the signal then the PCM could be causing the problem.
Since the speedo is reading 15 mph that should also put the car into skip shift mode. Is skip shift activating when you drive the car?
Does the DIC indicate any codes present?
Bill
Thread Starter
Burning Brakes
Joined: May 2007
Posts: 1,078
Likes: 5
From: Denver, North Carolina
Update:
Car sat overnight while I lost sleep thinking of what could be wrong. Went out this morning, got it cranked up, and speedo is back to normal and I could of course shift into reverse again. This problem may come back anytime if it's not just a fluke, so thanks for all the suggestions. So now I'm back to tracing down my 6 month intermittant no-start issue.
Car sat overnight while I lost sleep thinking of what could be wrong. Went out this morning, got it cranked up, and speedo is back to normal and I could of course shift into reverse again. This problem may come back anytime if it's not just a fluke, so thanks for all the suggestions. So now I'm back to tracing down my 6 month intermittant no-start issue.
Le Mans Master
Joined: Feb 2004
Posts: 8,629
Likes: 16
From: York PA
Update:
Car sat overnight while I lost sleep thinking of what could be wrong. Went out this morning, got it cranked up, and speedo is back to normal and I could of course shift into reverse again. This problem may come back anytime if it's not just a fluke, so thanks for all the suggestions. So now I'm back to tracing down my 6 month intermittant no-start issue.
Car sat overnight while I lost sleep thinking of what could be wrong. Went out this morning, got it cranked up, and speedo is back to normal and I could of course shift into reverse again. This problem may come back anytime if it's not just a fluke, so thanks for all the suggestions. So now I'm back to tracing down my 6 month intermittant no-start issue.
