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Solving Carbon Deposits In Direct Fuel Injection Engines

Symptom: Misfire codes, stumbling and suspicious fuel trim numbers. On a scan tool, the engine may show a loss in volumetric efficiency. The driver may complain about a loss of power, poor fuel economy and hard starts. Cause: Carbon deposits on...

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Selling the Complete Serpentine Belt Job

Technicians and customers have pretty much accepted that the accessory serpentine drive belt should be replaced between 90,000 to 100,000 miles. It is a “slam dunk” sale to just replace the belt, but does that replacement belt have the same chance...

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Gasket Guide: Match A Sealant With Every Type of Gasket

Cork/Composite Gaskets Sealants: Cork and composite gaskets can seal a variety of underhood applications from valve covers to carburetors. The type of sealant used with these gaskets depends on a variety of factors. First, you must consider if the...

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What to Know About Modern Air Ride Systems

GM, Ford, BMW and just about every other manufacturer has a 10-year-old vehicle on the road with an air ride suspension at the rear or at all four corners. These systems could be as exotic as a Land Rover Defender or as common as a Ford Explorer....

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Slipping Clutch: Improper Flywheel Step and Cup Dimensions

Slipping is one of the most common clutch related concerns. A slipping condition can occur after years of service or immediately after installation of a new clutch and is caused by various scenarios. One of the most commonly seen and easily prevented...

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Parking Brake Adjustments

The parking or emergency brake has to perform two distinct jobs. First, it must be able to hold the vehicle on an incline. Second, it must be able to stop a vehicle under a specific distance if the hydraulic brakes have failed. These standards are...

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Vehicle Unit Increase; Import-Rich VIO Are A Boon for Import Specialists

Need a dose of good news for your business? Then hear this: The influx of new vehicles in the market will lay the foundation for bountiful aftermarket service and repair opportunities. And, with import vehicle sales continuing an ­upward climb, there...

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Honda: Engine Shuts Off, But Power Mode Stays In ‘On’ or ‘Accessory’

Applies To: Honda Insight models with one-push start Customers might complain that when they shift into park and shut off the engine, that the power mode stays in On or Accessory. Honda says the culprit could be a misadjusted shift cable. If the...

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Import Oil Specification Primer

As engine technology has evolved and fuel efficiency standards have tightened, oil specs have increased in importance. Using the wrong viscosity could set a fault code in some applications or interfere with the normal operation of the variable valve...

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2015 Vehicle Lifting Points Guide Now Available

The Automotive Lift Institute, Inc. (ALI) announces the availability of the 2015 edition of ALI’s “Vehicle Lifting Points for Frame Engaging Lifts.” This updated guide is a quick-reference single-source manual for lifting point information as...

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Pulling Codes: P0302: Cylinder 2 Misfire Detected Intermittent Activity

  This article will address a misfire code from a different vantage point. It will look at a plan of attack for when a code is being set intermittently. The code we are referencing is P0302-Cylinder No. 2 Misfire Activity Detected. While...

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Registration Now Open For ToolTech 2015

The Equipment & Tool Institute (ETI) is hosting its ToolTech 2015 event April 13-16 at the Radisson Hotel and Suites in Downtown Austin, Texas. This year's theme is "The Connected Vehicle: Opportunities and Challenges." Information and technology...

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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.
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Andrew Markel

Andrew Markel is the editor of Brake & Front End and Servicio Automotriz magazines. He has been with Babcox Media for more than 12 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 posts by Andrew Markel (see all)

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Solving Carbon Deposits In Direct Fuel Injection Engines

Symptom: Misfire codes, stumbling and suspicious fuel trim numbers. On a scan tool, the engine may show a loss in volumetric efficiency. The driver may complain about a loss of power, poor fuel economy...More

Selling the Complete Serpentine Belt Job

Technicians and customers have pretty much accepted that the accessory serpentine drive belt should be replaced between 90,000 to 100,000 miles. It is a “slam dunk” sale to just replace the belt,...More

What to Know About Modern Air Ride Systems

GM, Ford, BMW and just about every other manufacturer has a 10-year-old vehicle on the road with an air ride suspension at the rear or at all four corners. These systems could be as exotic as a Land...More

Slipping Clutch: Improper Flywheel Step and Cup Dimensions

Slipping is one of the most common clutch related concerns. A slipping condition can occur after years of service or immediately after installation of a new clutch and is caused by various scenarios. One...More

Vehicle Unit Increase; Import-Rich VIO Are A Boon for Import Specialists

Need a dose of good news for your business? Then hear this: The influx of new vehicles in the market will lay the foundation for bountiful aftermarket service and repair opportunities. And, with import...More

Honda: Engine Shuts Off, But Power Mode Stays In ‘On’ or ‘Accessory’

Applies To: Honda Insight models with one-push start Customers might complain that when they shift into park and shut off the engine, that the power mode stays in On or Accessory. Honda says the culprit...More

2015 Vehicle Lifting Points Guide Now Available

The Automotive Lift Institute, Inc. (ALI) announces the availability of the 2015 edition of ALI’s “Vehicle Lifting Points for Frame Engaging Lifts.” This updated guide is a quick-reference single-source...More

Pulling Codes: P0302: Cylinder 2 Misfire Detected Intermittent Activity

  This article will address a misfire code from a different vantage point. It will look at a plan of attack for when a code is being set intermittently. The code we are referencing is P0302-Cylinder...More