Hi i ave 88 mustang manuel tranny problem is my speedometer is flucuating and cruise control is making up its own mind and about the sametime my voltage on the panel was dropping slowly for about a week.. my amp light goes on when i start the car and goes off when i boost the rpm and goes back on when is on idle.. Is the speed sensor able to mess around with the voltage gauge..... no problem starting.multimeter red 12 volts on battery and 12 when startedand running..u think if i change the sensor it will change the voltage on my gauge......help would be great
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Is there a check engine light on? If so, have the computer scanned for trouble codes that may point you in the right direction. If no light on, there still may be codes stored in the history portion of the computer. Possibly a vehicle speed sensor problem.
You could have a faulty speedometer/odometer combination meter causing a false Vehicle Speed Sensor error.
My 1998 Sienna had the following symptoms:
- Speedometer and odometer failed intermittently
- The check engine light would come on and I would get a p0500 code in the OBDII.
- The cruise control would stop working at the same time the speedometer failed.
There is a speed sensor in each one of the tires and they feed the speed information to the ABS ECU. From the ABS ECU the speed signal goes to the speedometer/odometer combination meter, and from there it goes to the Engine Control Module and to the Cruise Control ECU. I could see a signal coming into the speedometer/odometer, but no signal going out. Replacing the speedometer/odometer combination meter fixed the problem.
First I'll assume you haven't read the owners Manuel, Cruise control is not perfect on any vehicle. if coming to a hill put foot on gas to help rpm, going down hill put foot on brake to keep same speed, cruise control operates off of engine vacuum. Speed sensors can be affected by putting on smaller or bigger tires than what is on drivers door.
Problem is usually the speed sender failing when speed gets too high. In some case the speed gauge itself is damaged. In Mercury the speed sender is located in the transmission. The part is difficult to test without professional equipment. Repair is done replacing the speed sender. If that does not fix the problem, work on the instrument panel speedo.
The Haynes manual I have doesn't show another speed sensor either. However, if your speedometer is working then it must have either a speedometer cable or another speed sensor of some type. My 1987 Toyota Supra had a speedometer cable and the speed sensor was in back of the speedometer. It used a spinning disk attached to the cable. The disk broke and left me without cruise control. I don't know if you have a similar arrangement in addition to the transmission speed sensor.
I don't believe the cruise control will engage with a speed sensor DTC set or a faulty speed sensor. So the code must be erased even if you fixed the problem. If you erased the code after your fix and the code returned, try to determine if the speed sensor is getting the 5 volt reference voltage from the ECM. If not, then either a wiring problem or faulty ECM.
Check the VVS (vehical velocity sensor) "speed sensor", The vss controls shifting and cruise control as well as speedometer. If the Cavalier shift's fine and cruise control work, the it's going to be a good chance that the speedometer n the instrument panel may have a bad connection or the stepper motor needs to be replaced. Get a service book and attempted to check for voltage going to speedo cluster( at dash), to determine if your stepper motor is bad and replace the motor or the whole instrument panel. Good luck and thank you for using fixya.
A vehicle speed sensor that is starting to fail could cause this, or less than likely bad wiring or connections, or yes, a bad cluster could do this... But how exactly did she notice the speedometer was 10MPH fast?? There are no real accurate speedometers in vehicles (Don't get me wrong they shouldn't be off by 10MPH) but there is a 5 or so percent difference high or low in many vehicles even with stock powertrains. I've plugged in with a diagnostic scanner on many vehicles and the dash speedo shows 60MPH, but the electronic speed readout on the scanner reads as low as 55MPH or as high as 65MPH
does your cruise control work? If not, check the wiring from the VSS to the speedo cluster. Check VSS connector closely for pin pudhout or corrosion
Sometimes, the VSS siganl is converted by the instrument cluster and sent to the PCM and speedo.
Check engine light on?
The electronic speedometer (17255) receives a speed signal from the vehicle speed sensor (VSS) (9E731). This sensor is also used to sense vehicle speed for the engine management system and to regulate the cruise control when equipped.
Vehicle Speed Sensor
The Vehicle Speed Sensor (VSS) (Figure 53) is a variable reluctance or Hall-effect type sensor that generates a waveform with a frequency that is proportional to the speed of the vehicle. If the vehicle is moving at a relatively low velocity, the sensor produces a signal with a low frequency. As the vehicle velocity increases, the sensor generates a signal with a higher frequency. The PCM uses the frequency signal generated by the VSS (and other inputs) to control such parameters as fuel injection, ignition control, transmission/transaxle shift scheduling and torque converter clutch scheduling.