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What might cause a speedo to be wrong?
Thread Starter
Instructor
Joined: Feb 2003
Posts: 165
Likes: 1
From: Lawrence KS
What might cause a speedo to be wrong?
Its been wrong since I have had the car. Its about 6mph off at 55 on the speedo itself however, the cruise control is correct so I have to go by that.
Obviously the computer knows the correct speed but the speedo shows it as much slow than it really is. What could cause this?
Obviously the computer knows the correct speed but the speedo shows it as much slow than it really is. What could cause this?
Melting Slicks
Joined: Jan 2007
Posts: 3,333
Likes: 0
From: Athens OH
*edit* Nevermind. i see you said it was slower.
Last edited by AMRAAM; Feb 12, 2008 at 10:25 PM.
Team Owner
Joined: Apr 2001
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From: S.W. Ohio. . . . . . NRA Life Member
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 30
From: San Rafael CA
Its been wrong since I have had the car. Its about 6mph off at 55 on the speedo itself however, the cruise control is correct so I have to go by that.
Obviously the computer knows the correct speed but the speedo shows it as much slow than it really is. What could cause this?
Obviously the computer knows the correct speed but the speedo shows it as much slow than it really is. What could cause this?
There is a sensor located at the rear of the vehicle called the Vehicle Speed Sensor (VSS). The IPC uses the output from this sensor to display the vehicle speed digitally (on the HUD) and in analog format (the speedometer). The PCM and TAC also use this same sensor to control the Cruise Control speed.
Are you saying that the speedo displays 55 MPH but if you set the Cruise Control it says it is set for 61 MPH ???
I'd do two things (your profile does not list what car you have so I'm gonna assume you have a HUD) ...... first compare the HUD and speedo displayed speeds (they should agree) .... if they don't, a handheld GPS unit (borrow from friend if you don't have one) will tell you the ACTUAL speed of the vehicle. Then you should have the information to determine if the VSS is providing bad data (unlikely unless your tire sizes are way off) or the IPC speedo is incorrectly displaying data.
If you determine the speedo is displaying the wrong speed, I'd call these guys and see if they can service the IPC.
http://www.paspeedo.com
Last edited by BlackZ06; Feb 13, 2008 at 12:01 AM.
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Thread Starter
Instructor
Joined: Feb 2003
Posts: 165
Likes: 1
From: Lawrence KS
I've used a GPS unit before and it puts the actual speed 1MPH faster than the speed the cruise control indicates. I do not have HUD so I cannot compare that.
However, the speedometer constantly reads 5 to 7 MPH slower than what the cruise controls reads.
In addition to this I know the TAC is correct because it reads the correct RPM at a real vehicle speed of 70mph
However, the speedometer constantly reads 5 to 7 MPH slower than what the cruise controls reads.
In addition to this I know the TAC is correct because it reads the correct RPM at a real vehicle speed of 70mph
Last edited by Montezumas_Viper; Feb 14, 2008 at 01:38 PM.
Le Mans Master
Joined: Sep 2004
Posts: 5,707
Likes: 4
From: Los Angeles
It should be accurate between the average speed and what you set on the cruise. If the speedo is off from those, then the problem is the speedo itself.
Intermediate
Joined: Feb 2008
Posts: 36
Likes: 0
From: Princeville IL
speedo
another possibility is that the wire that hooks up to the back of the speedo may be loose, or not connected correctly, which in turn causes the wrong speed to be displayed... my 2 cents...
Thread Starter
Instructor
Joined: Feb 2003
Posts: 165
Likes: 1
From: Lawrence KS
Ok, you don't have HUD but you have an average speed display on your DIC. Reset the DIC average speed, then set the cruise for a desired speed, then after a few miles, tell us if the DIC coincides with the speed you set on the cruise and what is displayed on the speedo during that time.
It should be accurate between the average speed and what you set on the cruise. If the speedo is off from those, then the problem is the speedo itself.
It should be accurate between the average speed and what you set on the cruise. If the speedo is off from those, then the problem is the speedo itself.
I've done this an have come up with almost the exact same average speed as my cruise speed so the computer definately knows the correct speed. It must be the speedometer itself, what do I do now?
Safety Car
Joined: Aug 2000
Posts: 4,933
Likes: 30
From: San Rafael CA
http://www.paspeedo.com
If they can, you will need to remove the IPC (the unit that includes the gauges), pack it well, and ship it to them.
Otherwise, you will need a new IPC, and again paspeedo can program the new IPC with your current odometer reading. A dealer can order a new IPC, but they will have to send it out to get the odometer set as dealers can't do that, the IPC has to have a special "tool" used to change the odometer.
