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H03000 - My RAC-100/RAC-200 won't count. What's wrong?
In most cases, when a RAC-100 or 200 won't count, it is not the unit itself that has the problem. It is usually a
problem with the interface sensor or wiring. Check the following:
1. Check that there is a calibration number stored in memory. The unit will not count if there is no calibration
number. To check this, when you switch on the unit the display will show CF followed by a four digit calibration
number. If this number is all zeroes, the unit will not count. The factory uses .900 as the default number.
2. Be sure that you are attached to the speed sensor output. It is generally at the transmission or the rear
differential. If you are unsure about being attached to the correct output, disconnect the plug and move the vehicle.
If the speedometer does not function, you have chosen the correct plug wires.
3. Perform a Sensor Test. Locate the Sensor Test button on the front upper right of the Modular Distance Sensor
(MDS). When pressed, this will generate an internal low-level signal that is fed directly into the VSS Input circuit.
First, unplug the VSS Input connector from the right side of the MDS. Second, turn on the RAC and press the C-
HOLD key just like you would prior to starting a measurement. Next, using a small pointed object (pen, pencil,
screwdriver, etc.) or your finger press the Sensor Test button for a few seconds. The RAC should count when the
button is pushed. What number it counted doesn’t matter as long as it did count.
If the RAC did count, everything from the MDS up to the RAC is okay and the problem is most likely a poor
connection at the vehicle’s speed sensor. Make sure you have a good electrical connection at the tap in point.
Once you are sure you tapped into the correct location, it is always better to wire solder the connection.
After checking the connection, plug the VSS Input connector back into the MDS and try the RAC again.
4. Perform a Tap Test. The Tap Test will determine if the distance pulses being sent from the MDS are getting to,
and being processed by, the RAC. The Tap Test is performed using the rotary switch on the MDS. First make sure
you note the current position of the rotary switch (1, 2, 4, 8,16, 32 or 64), as you will have to return the slot back to
this same position after the test is completed.
Next, turn on the RAC. Press the C-HOLD key just like you were beginning to measure. Using a small screwdriver,
rotate the switch between the Tap and Test positions four or five times. (Note that when the switch is turned
clockwise until it stops, it is at the Test position.) The RAC should register. The count shown does not matter, just
as long as the RAC did register a count. If it did count, the cable from the MDS to the RAC and the instrument itself
are OK. If the RAC did not count, the problem is most likely a bad cable to the RAC or the RAC itself is bad. If
available, try another RAC and repeat the Tap Test. If the second RAC doesn’t count, the problem has to be the
cable between the MDS and the RAC.
Once the test is complete, return the Rotary Switch to the previous position.
H03000 - My RAC-100/RAC-200 won't count. What's wrong?
In most cases, when a RAC-100 or 200 won't count, it is not the unit itself that has the problem. It is usually a
problem with the interface sensor or wiring. Check the following:
1. Check that there is a calibration number stored in memory. The unit will not count if there is no calibration
number. To check this, when you switch on the unit the display will show CF followed by a four digit calibration
number. If this number is all zeroes, the unit will not count. The factory uses .900 as the default number.
2. Be sure that you are attached to the speed sensor output. It is generally at the transmission or the rear
differential. If you are unsure about being attached to the correct output, disconnect the plug and move the vehicle.
If the speedometer does not function, you have chosen the correct plug wires.
3. Perform a Sensor Test. Locate the Sensor Test button on the front upper right of the Modular Distance Sensor
(MDS). When pressed, this will generate an internal low-level signal that is fed directly into the VSS Input circuit.
First, unplug the VSS Input connector from the right side of the MDS. Second, turn on the RAC and press the C-
HOLD key just like you would prior to starting a measurement. Next, using a small pointed object (pen, pencil,
screwdriver, etc.) or your finger press the Sensor Test button for a few seconds. The RAC should count when the
button is pushed. What number it counted doesn’t matter as long as it did count.
If the RAC did count, everything from the MDS up to the RAC is okay and the problem is most likely a poor
connection at the vehicle’s speed sensor. Make sure you have a good electrical connection at the tap in point.
Once you are sure you tapped into the correct location, it is always better to wire solder the connection.
After checking the connection, plug the VSS Input connector back into the MDS and try the RAC again.
4. Perform a Tap Test. The Tap Test will determine if the distance pulses being sent from the MDS are getting to,
and being processed by, the RAC. The Tap Test is performed using the rotary switch on the MDS. First make sure
you note the current position of the rotary switch (1, 2, 4, 8,16, 32 or 64), as you will have to return the slot back to
this same position after the test is completed.
Next, turn on the RAC. Press the C-HOLD key just like you were beginning to measure. Using a small screwdriver,
rotate the switch between the Tap and Test positions four or five times. (Note that when the switch is turned
clockwise until it stops, it is at the Test position.) The RAC should register. The count shown does not matter, just
as long as the RAC did register a count. If it did count, the cable from the MDS to the RAC and the instrument itself
are OK. If the RAC did not count, the problem is most likely a bad cable to the RAC or the RAC itself is bad. If
available, try another RAC and repeat the Tap Test. If the second RAC doesn’t count, the problem has to be the
cable between the MDS and the RAC.
Once the test is complete, return the Rotary Switch to the previous position.