ABS
What controls pressure build and release in the ABS system?
The Hydraulic Modulator
What systems can the TCS work with to prevent wheel slip?
Customer states: I have to top off my brake fluid everyday. Upon visual inspection you find no external leaks.
What could be the cause of the concern?
A leaking rear master cylinder seal, causing fluid to leak into the brake booster.
What does hydroscopic mean?
Moisture Absorbing
Customer states: My TCS and ESC light are on. Upon inspection you find no defects in the system and no codes in the ABS. There is a MIL light on with a P0300 Random Multiple Misfires Detected.
What could be disabling the TCS/ESC?
Some systems will disable the TCS/ESC when they have a fault, since those systems work with the TCS/ESC to control wheel slip and steering propblems.
How many times per second can the ABS unit cycle the brakes?
20-30 times per second
What safety system does the ESC work with?
SRS/Airbag system
Customer states: My brakes grab on light braking in my truck. Upon inspection, you find sagging rear leaf springs.
What could cause this condition?
The load sensing proportioning valve needs to be adjusted to the lower than normal ride height. This is causing excessive pressure on light braking.
Other than test strips, how can I tell if a fluid has absorbed moisture?
Dark and cloudy
Customer states: I replaced my brake pads, and now my vehicle won't stop and there is a grinding noise coming from the front of the vehicle.
What is the most likely cause of this concern?
Brake pads installed backwards. With no friction material the vehicle would be hard to stop and the grinding is the backing plate pressing against the rotor.
What is the main purpose of the ABS system?
To prevent wheel lock up
What part of the ESC system, measures vehicle position on its center axis?
Yaw Rate Sensor
Customer states: My ABS is actuating without needing to. Upon inspection you find no ABS faults, and the system works as designed.
What could be causing the customer concern?
Warped Rotors. A warped rotor will cause pedal pulsation, which could feel like an ABS actuation event.
How does moisture effect brake fluid? What is the condition it causes?
Customer states: When I step on the brake it pulls to the left. Upon inspection you find the RF inner brake pad worn and the outer pad in good condition.
What is the most likely cause of this concern?
RF caliper piston seized, causing no braking on RF side, will cause vehicle to pull to the side with a functioning caliper.
What are the 3 stages of ABS operation?
Isolate, Dump, Reapply
What conditions does ESC prevent?
Understeer, oversteer
Customer states: My brake warning light comes on only when I step on the brake pedal, when I let go the light goes off. Upon visual inspection, you find a small leak at the RR brake hose.
What is causing the light to only come on with pedal use?
A self centering pressure differential switch. When the pedal is applied, there is a loss of pressure in the rear, causing the light to illuminate. When the pedal is released the switch re-centers and the light goes off.
If the proportioning valve goes bad in a combination valve, can I service it?
No, combination valves are serviced as a unit.
Customer states: When I try to brake the pedal feels very hard and the vehicle doesn't want to stop. Upon inspection the vehicle has normal engine vacuum and the brake booster is not defective.
What could cause this condition?
A faulty vacuum check valve, if the vehicle has good vacuum and the booster isn't faulty test the check valve to see if it holds vacuum, if it doesn't the booster won't be able to function.
What items are tested during a key on Self Test?
Valve Solenoids, Pump Motor, all relays and electrical devices in system to ensure proper function.
Can improperly sized tires effect TCS operation? Why?
Yes, wheels with a greater diameter will roll slower than one with a smaller diameter.
Customer states: My pedal sinks to the floor, but after I press the pedal a few more times it gets solid and holds.
What is the most likely cause of this concern?
Rear shoes out of adjustment. When shoes are out of adjustment it takes more pedal travel to overcome spring tension, sometimes a couple pumps before the brakes will hold.
What are the 5 bleeding techniques to remove air from the hydraulic system?
Manual, Gravity, Vacuum, Pressure, Reverse
Customer states: My brake pedal is squishy. Upon inspection you find a leaky LF brake hose. You replace the hose and bleed the brake system. During your test drive the vehicle still has a spongy pedal.
What is the most likely cause?
The ABS unit has air present in it, an automated bleed needs to be performed, the secondary system needs to be bled afterwards.