Wheel Speed Sensor test
Thread Starter
Racer
Joined: Jan 2005
Posts: 418
Likes: 45
From: Houston Texas
Wheel Speed Sensor test
I want to check (bench test) the wheel speed sensors (ohm test) on my 96 LT-1.
Other GM car service manuals show the specific resistance for each sensor (front or rear). However, I cannot find such a value in my FSM for 96. Can anyone help..?
Also, on page 5e2-20 of the FSM, it shows the Brake Module connector and lists the wires for each terminal.
Terminal 16 is described as Left Front Wheel Sensor (HI)
Terminal 17 is described as Left Front Wheel Sensor (LO).
What does the HI & LO refer to..? wheel speed..? electrical signal..?
In researching my other car manuals, the HI circuit is also described as the "signal" whereas the LO circuit is described as the "return".
This would imply that the Brake Module sends a reference signal (or voltage) to the wheel, and depending on the wheel speed, the signal returning is variably diminished by the resistance in the sensor. Can anyone confirm this..?
Last Question--in the ABS system, what would be a likely cause for "Service ABS" to set ONLY when speeds are above 50 mph after exactly 1 mile. I can drive all day below 50 and not have it set.
Other GM car service manuals show the specific resistance for each sensor (front or rear). However, I cannot find such a value in my FSM for 96. Can anyone help..?
Also, on page 5e2-20 of the FSM, it shows the Brake Module connector and lists the wires for each terminal.
Terminal 16 is described as Left Front Wheel Sensor (HI)
Terminal 17 is described as Left Front Wheel Sensor (LO).
What does the HI & LO refer to..? wheel speed..? electrical signal..?
In researching my other car manuals, the HI circuit is also described as the "signal" whereas the LO circuit is described as the "return".
This would imply that the Brake Module sends a reference signal (or voltage) to the wheel, and depending on the wheel speed, the signal returning is variably diminished by the resistance in the sensor. Can anyone confirm this..?
Last Question--in the ABS system, what would be a likely cause for "Service ABS" to set ONLY when speeds are above 50 mph after exactly 1 mile. I can drive all day below 50 and not have it set.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Measuring d.c. ohms will only find gross sensor problems. You will learn a lot more about the condition of the sensor by measuring its inductance and Q with an impedance bridge and comparing it against your other sensors. ABS works by sensing if the wheels are all turning at the same speed via a spoked wheel that makes pulses in the wheel sensor. A gross difference causes the ABS to pulse the brake line pressure as it believes one wheel is badly slipping. Good GM dealers have an ABS system tester where you jack up the car and follow the tester commands which tells you to spin each individual wheel. It found a bad LR sensor on my 87 which by my measurements was identical to the other sensors.
Team Owner
Joined: Mar 2001
Posts: 54,124
Likes: 30
From: Cincinnati, Oh USA
Hehehehehe, I cheated, I wasn't charged anything for the test! My mechanic is a vette mechanic for a GM dealer and he brought their C4 ABS tester home and it found a defective LR sensor. He replaced it for a lot less than the dealer gets! 
