NN2 Check Rear Axle Speed Sensor Output at ABS Module

- Lower vehicle so that wheels are just far enough off the ground to permit all wheels to turn.
- Verify transfer case is in the 4x2 mode.
- Start engine and allow rear wheels to spin and stabilize at engine idle speed.

NOTE: Examine the ring carefully with good light. Failure to catch issues with the tone ring will lead to unnecessary component replacement and wasted diagnostic time.

- Set the Rotunda(r) Digital/Analog Volt-Ohmmeter 105-00053 or equivalent, to the frequency counter (Hz) setting. Measure and record the frequency between Pins 21 and 22 on the Rotunda(r) Breakout Box 014-00322 or equivalent.
- Change the meter to the A/C mV setting. Measure and record the voltage output between Pins 21 and 22 on the Rotunda(r) Breakout Box 014-00322 or equivalent.
- Determine the speed sensor output in mV/Hz - Output -- A/C Voltage/Frequency

NOTE: Measurements of BOTH the frequency and the voltage output must be taken. The actual speed the wheels are turning is not important -- the result of voltage output divided by the frequency will not change with wheel speed. However, it is crucial that both the frequency measurement and the voltage measurement be taken at the same wheel speed.

- Is the sensor output greater than 6.0 mV/Hz?

YES -- Output at anti-lock brake control module indicates that the air gap and sensor strength are OK. GO to NN4. NN4 Check For Wiring Intermittents

NO -- Sensor output at ECU is insufficient. GO to NN3. NN3 Check Rear Axle Sensor Output at Speed Sensor