AfterMarketNews AfterMarketNews Auto Care Pro AutoCareCareerHub Brake&Frontend BodyShopBusiness Counterman EngineBuilder Fleet Equipment ImportCar Motorcycle & Powersports News Servicio Automotriz Shop Owner Tire Review Tech Shop Tomorrow's Tech Underhood Service Speedville

Aftermarket TPMS Sensors and Scan Tools

Aftermarket TPMS Solutions Servicing tire pressure monitoring systems (TPMS) can be a quick money-maker that requires minimal labor. The service is also essential since this maintenance applies to every vehicle made or sold in the U.S. since 2008. Manufacturers...

Read more...

Fuel Tank Installation: Avoiding the Second Drop

Nothing is worse than a comeback after a fuel tank has been dropped. Discovering that the fuel tank needs to be dropped again to address a problem can kill shop productivity and profitability. Below are tips that can help you avoid comebacks and dropping...

Read more...

Correct Fuel Hose Installation

Understanding the Differences Between Fuel Hoses Fuel hoses are not universal. Outside of the dimensional requirements, fuel hoses have requirements for permeation, pressure and the type of fuel they can carry. This can get even more confusing when...

Read more...

Electric Power Steering Diagnostics

Understanding Electric Power Steering Systems Electric power steering, or EPS, is more energy efficient than hydraulic systems and does not provide assist until it receives driver input. The steering wheel position sensor and applied torque sensor are...

Read more...

How to Test Drive a Car to Check for Problems

Test Drive Diagnostics Test drives on the surface can seem like one of the most unprofitable tasks a technician can perform. But, test drives can be one of the most profitable processes a shop can do to help sell more service. You just have to have procedures...

Read more...

Cheap Brake Pads

The Real Cost of Installing Cheap Brake Pads Ever since the first issue of Brake & Front End came off the presses, the magazine has warned of the costs of using inferior friction materials with brake pads. In the 1930s, the magazine fought the fight...

Read more...

Hyundai No-Start, No-Crank Condition Due to Gear Selector Range Switch

Affected Models: Tucson (2010-); Santa Fe (2010-12); Sonata (2011-); Elantra (2013-); Accent (2012-); Azera (2012- ); and Veloster (2013-). Condition: An improperly adjusted or improperly operating inhibitor switch (range switch) may result in...

Read more...

Be Wary of the Fall Maintenance Slowdown

If you think you don’t need to do any more marketing this quarter because you’ve been riding the summer vehicle maintenance wave, think again. While your car count is likely high — due to road trip inspections, oil changes, A/C service and unperformed...

Read more...

Honda Civic: Failed PCMs and CAN System Diagnostics

It’s not unusual for me to get help requests through my e-mail. Sometimes it’s from working technicians, other times it’s from vehicle owners who can’t get their problems solved through professional repair shops. In early 2014, I received one...

Read more...

Identifix Celebrates 50,000 Direct-Hit Subscribers with 50K Giveaway Contest

Identifix, Inc. has reached another milestone: its 50,000th subscriber to Direct-Hit, its award-winning online tool. To commemorate the occasion, the company has launched a contest called the 50K Giveaway. Five Direct-Hit users who submit a Hotline...

Read more...

Liquid Tools: Choose Your Maintenance Chemicals Based On The Application

The shelves in most parts stores are stocked with an abundance of aerosol maintenance products – everything from cleaners to lubricants. The huge selection of products can be overwhelming, leading to confusion about which product you should purchase...

Read more...

Snap-on Franchisee Conference Draws Record Crowd

Snap-on reports that it drew a record-setting crowd for its Snap-on Franchisee Conference (SFC) held in Washington, D.C., this year. The three-day business conference brings together Snap-on Tools franchisees for insight, information and celebration...

Read more...
REAPPLY
Since pressure from the master cylinder has been bleed off, the pump in the HCU will spool up and apply pressure. The outlet valve is closed and the inlet valve is opened. The pump applies pressure to the wheel. 
If the wheel is still outside the wheel slip parameters, the cycle will start over. This happens very quickly. The operation of the solenoids and pump will cause a “kick back” or pulsation in the pedal. 
 

HCU Mechanical Problems
Mechanical issues with the HCU are rare, but they can happen. Valve seats and pintles can become stuck or not seat properly due to debris, corrosion or contaminated brake fluid. 
 
If the inlet/isolation valve is stuck open, it will not affect normal braking in any way. It will only hurt the ABS system. This could lead to a pulling condition during ABS activation. 
 
If an outlet/dump valve is stuck open in one circuit, this could cause a pull condition during normal braking. This is due to the loss of brake pressure at a wheel. Typically, this is not discovered until brake hoses, calipers and other parts have been replaced.

Testing Solenoids Electrically
Sometimes a stuck or defective solenoid or pump will set a code. A solenoid has a resistance between 2 and 8 ohms. On some units, it is impossible to access the individual solenoids. 
 
Testing of the unit with a scan tool with bi-directional control might be the best way to confirm the condition of the HCU.
 
Most vehicles equipped with ESC will have 12 valves or solenoids in the HCU. Eight solenoid control the wheels. Four additional solenoids can block off the master cylinder and allow the pump to send pressure to a specific wheel.
 
Understeer is a condition where the wheels are turned, but the vehicle continues to travel in a straight line. This is sometimes described as a push. 
 
The ESC computer would see this event through the sensors. The wheel speed sensors in the front typically read slower than the rears. The computer would also see that the steering angle is greater than the intended path.
 
The ESC system needs to intervene before the event occurs. It needs to anticipate the problem and correct as the vehicle travels.
 
This is what the ESC sees during an understeer event. The SAS angle is at +52º, this means that the customer has the wheel turned to the right at a significant angle. Even with the steering wheel turned, the yaw and accelerometer read like the vehicle is going straight. 
 
 The APPS or throttle pedal position sensor shows the driver is off the gas and the brake pedal is not pressed.
 
The deciding information for the system is in the wheel speed sensor inputs. Between the front and rear there is a 6 to 9 mph difference between the front and rear speeds. The front wheels are traveling slower than the rears.
The following two tabs change content below.

Andrew Markel

Andrew Markel is the editor of Brake & Front End, Underhood Service and Servicio Automotriz magazines. He has been with Babcox Media for more than 15 years. He is a technician and former service writer and holds several automotive certifications from ASE and ­aftermarket manufacturers. He can be reached at [email protected]
Latest articles from our other sites:

Aftermarket TPMS Sensors and Scan Tools

Aftermarket TPMS Solutions Servicing tire pressure monitoring systems (TPMS) can be a quick money-maker that requires minimal labor. The service is also essential since this maintenance applies to every...More

Fuel Tank Installation: Avoiding the Second Drop

Nothing is worse than a comeback after a fuel tank has been dropped. Discovering that the fuel tank needs to be dropped again to address a problem can kill shop productivity and profitability. Below are...More

Electric Power Steering Diagnostics

Understanding Electric Power Steering Systems Electric power steering, or EPS, is more energy efficient than hydraulic systems and does not provide assist until it receives driver input. The steering...More

How to Test Drive a Car to Check for Problems

Test Drive Diagnostics Test drives on the surface can seem like one of the most unprofitable tasks a technician can perform. But, test drives can be one of the most profitable processes a shop can do...More

Hyundai No-Start, No-Crank Condition Due to Gear Selector Range Switch

Affected Models: Tucson (2010-); Santa Fe (2010-12); Sonata (2011-); Elantra (2013-); Accent (2012-); Azera (2012- ); and Veloster (2013-). Condition: An improperly adjusted or improperly operating...More

How to Test Drive a Car to Check for Problems

Test Drive Diagnostics Test drives on the surface can seem like one of the most unprofitable tasks a technician can perform. But, test drives can be one of the most profitable processes a shop can do...More

Wireless Connectivity In The Bay From Launch Tech

The PAD II from Launch Tech is a robust, drop-tested and waterproof Android-based scan tool tablet with a 10.1” ultra-high resolution IPS touch screen. The PAD II boasts the same award-winning software...More

Lisle Offers Self-Adjusting Wire Stripper

The Self-Adjusting Wire Stripper (68220) from Lisle Corp. automatically adjusts to strip insulation from 10 to 24 gauge wire. This tool crimps insulated and non-insulated terminals from 10 to 22...More