*Refreshing this page at any point will restart the troubleshooting guide.
First, please reference the manual for the sensor in question. Each sensor has unique requirements for gear pitch and speed; and will be referenced throughout the troubleshooting process. This guide assumes that the device is properly configured to accept a sinking input.
Manuals
HESS - HALL EFFECT SPEED SENSOR
PSAH - HALL EFFECT SPEED SENSOR
Verify that the unit is being powered
Red Lion Hall Effect sensors require 8-30VDC power.
Is the sensor powered properly? 
Correct the power wiring.
Did correcting the power resolve the issue?
Verify that the sensing gear is made of a magnetic material.
Hall Effect speed sensors use a magnetic field to detect the gear's movement.
Is the gear made of magnetic material?
Replace the gear with one made of magnetic material, or replace the sensor with one that can detect non-ferrous materials.
Verify that the sensing gear has a propper pitch for the sensor.
The larger the gear pitch value, the smaller the gear teeth will be. The minimum gear pitch is the smallest size tooth that the sensor can detect. There must also be a gap between the targets (gear teeth) greater than or equal to the size of the target. Red Lion's Hess Sensors can detect gears as small as 24 D.P. or other ferrous targets with equal or greater dimensions.
Does the gear have the correct pitch?
Replace the gear with one that has the correct pitch, or replace the sensor with one that can sense the existing gear.
Verify the air-gap between the sensor and the gear.
All Red Lion Hall Effect sensors require a maximum of 0.040" (1 mm) air-gap.
*note that a standard credit card is 0.03" thick
Is the air-gap correct?
Correct the air-gap.
Verify that the gear is moving at the correct speed.
All Red Lion Hall Effect sensors have a maximum speed of 10KHz.
Is the gear moving at the correct speed?
Replace the gear, sensor, or monitoring device to achieve a working system.
Verify the output voltage and frequency.
Connect a 5.1K ohm resistor between the signal line and the positive side of the power supply. Use an oscilloscope to verify the output voltage and frequency.
Is the pickup outputting a signal?
It sounds like a bad sensor.
It sounds like a bad meter.
Please contact Technical Support.
Call us on the toll-free Tech Line: 877-432-9908 or the Support button on the lower right to fill out a contact form.
Congratulations, you have resolved the issue.
Disclaimer
It is the customer's responsibility to review the advice provided herein and its applicability to the system. Red Lion makes no representation about specific knowledge of the customer's system or the specific performance of the system. Red Lion is not responsible for any damage to equipment or connected systems. The use of this document is at your own risk. Red Lion standard product warranty applies.
Red Lion Technical Support
If you have any questions or trouble contact Red Lion Technical Support by clicking here or calling 1-877-432-9908.
For more information: http://www.redlion.net/support/policies-statements/warranty-statement