The Honda Speed Sensor's main purpose is to transmit speed data to the TCU, ECU, speedometer gauge and the cruise control unit. It is reading the frequency of a bobbin that is attached to upper casing that speeds past the pickup sensor. The bobbin is a cylindrical or spool-shaped coil or insulated wire, usually containing a core of soft iron which becomes magnetic when the wire is traversed by an electrical current.
 -----------------  ---------------------- The faster the wheel spins, the faster the frequency the wheel magnet moves past the sensor thus the higher speed reading on your speedometer. The vehicle speed sensor counts the revolutions of the transmission output shaft. For a given vehicle, the Transmission Control Module considers a certain number of revolutions to equal a mile. A defective speed sensor can either set off the "S" light or fail to engage the cruise control, which also can affect other system controls. The result is that the TCU thinks the vehicle is running at zero speed from what it’s actually doing. The first thing you notice is an intermittent speedo reading then followed by a transmission error code after decellerating from a moderately high speed. The error codes will reset after every ignition off/on cycle. Problem: The usual problem with the Honda/Acura vehicle speed sensor is the conducting surface wearing too soon. Once the surface begins to wear itself into the pit (of dirty grease) (see illustrated below) the speed sensor will stop working and throw out two codes below, usually at around 130 - 150K miles.
Typical FAQ: Will the transmission shift normally to all gears (1-4, plus lockup) when the speed sensor is broken or removed? Yes. The transmission will shift up as usual. The VSS is mainly required for a proper downshift such as for descending from a hill. It will also shut off the engine if the speed is excessive. A failed VSS often won't create a limp mode. But most TCU's may go into a "limp mode" when there is a detected fault. The limp mode is usually mistaken for a transmission problem when the transmission refuses to shift. Please check for a stored code.
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← Schematic diagram 2
| A = Blk (ground) B = Yellow(12V battery) C = Orange(output 5V pulses, to ECU, TCU and gauge) |
Connect negative ground to A = Blk.
Connect the positive terminal of the multimeter to C = Orange and the black negative of the multimeter to A = Blk .
Spin the drive link by hand.
There should be voltage readings from 0V to 5V on C (orange) terminal as you spin the drive link.
How to check the speedo/ Speedo troubleshooting: Checking for vehicle speed signal at the gauge.
Steps:
Remove the instrument gauge and look for an orange wire located on one of the harness connector on the back of the instrument gauge.
Check the orange wire at the instrument gauge for 5V pulses.
Attach your probe on the orange wire (disconnecting the harness is okay) and the other probe to a body ground. If there are two or three orange wire on one or more connectors, pick the wire that has the "VSS pulses."
Drive the vehicle slowly.
If the voltage jumps from 5V to 0V repetitively when the car is moving then the speedo is most likely dead.
Author's note: The speedo is reliable device. A dead speedo or a dead rpm meter is most likely caused by the speedo bumping itself out of calibration or had jarred and cracked its circuit board solder joints (probably from an odometer tampering.) To attempt to calibrate the speedo to circuit board screw pressure, screw the three or four screws on the back of the circuit board to the correct screw torque then drive the car. Do this every mile until all the screws are at the correct point. For example. All three screws torque to 0.1 ft-lb in a crisscross manner at first attempt. Increase the torque on all screws at the next attempt in the same manner until the speedo works. This is an unconventional method but it works all the time for us but there is no guarantee for you.
How to remove the dash panel and locate the calibration ports click here.
Signs of a faulty NM speed sensor: Located at the end of the transmission on some models, check for code 15 or transmission jerks hard when shifting. The NM speed sensor should be within 400-600 Ohms at 20-degrees C. See transmission.html#nc for details
VSS Removal:
Locate the VSS on top of the power steering speed sensor near the firewall on the passenger side, just below the throttle body or the fuel filter. Unplug the VSS connector by squeezing in the locking tab. Remove the bolt(s) that will fit a 10-mm socket wrench. Remove the VSS unit by lifting and twisting the unit upward. (Caution: Do not loose the drive link)
LOCATION
Figure 1
OVERHAUL/REBUILD
Remove the VSS's two phillips screws and gently lift the top off for inspection. Caution: DO NOT allow the spring pop out carelessly. If you loose track of it then you may have a hard time putting the parts back in correctly (since the drawings aren't as detailed. And their are no service manual drawings.)
Figure 2
Inspect for signs of wear between the conducting rod and the conducting surface. The rod can be rounded off with a 400-600 grit sandpaper. The conducting surface on the opposite end can be treated the same way. Note: Add conducting grease to the treated areas when done.
Figure 3
The new, improved polished surface should appear smooth, clean and shiny. If you want to get a near mirror polish use standard automotive finishing wet-dry papers....add a little diamond polishing paste up to 1 micron grade. Or use something like a ceramic sharpeners.
TOOLS REQUIRED
Figure 4
Technical details
KNOWN GOOD READING
Other models:
Make: Acura
Model: 3.2TL
Year: 2003
Pulse Type: Digital
Color/Location: (YEL/RED, Blue/White, and GRN) Blue/White pulses - Pin 2
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