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Oil-Related Engine Codes for VVT Engines

Variable valve timing is becoming a standard system on most late-model engines because it offers higher performance from a smaller displacement engine at higher rpms. Oil plays a larger role in VVT systems. They need engine oil not only for lubrication,...

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Head Gasket Do’s and Don’ts

DO: Clean the holes. To ensure accurate torque values and to avoid cracking the cylinder block, clean any dust, dirt, oil and fluid from the cylinder block head bolt holes before installing the new head gasket and head bolts. Never lubricate the...

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Harmonic Dampeners: Why They Fail, What to Look For

Every time a cylinder fires, the crankshaft speeds up a very small amount for a short period of time. It is then slowed down as the next cylinder in the firing order compresses air and fuel for the next combustion event. The speeding up and slowing...

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TPMS Service Tip: Ask the Right Questions

If there is one piece of major advice for any tire tech facing a TPMS issue, it would be this: Test before you touch, and document the answers you get. Understanding the potential TPMS land mines can save time and money and eliminate frustrations. Get...

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False ABS Activation After Wheel Bearing Hub Replacement

Vehicles: All ABS-equipped vehicles Condition: Vehicle had wheel bearing hub replaced on one side. Repair Procedure: If you diagnose a bad hub bearing on one side of a vehicle and the ABS wheel speed sensor or tone ring is integral to the bearing,...

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Are you afraid of selling alignments?

I am starting to notice a trend when it comes to alignments. It’s not the vehicles that are changing, but rather the attitudes toward alignment services — and it happens at independent repair shops, franchise shops and even dealers. The alignment...

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Mazda: Performing Regular Undercar Maintenance

This month, we’ll take a look at brake and undercar service on the Mazda vehicle lineup, with the footnote that even though this type of work ­becomes routine when you have a preventive maintenance mindset, good work habits from beginning to end are...

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Import Automatic Transmission Diagnostics

Don’t be alarmed if you pull an automatic transmission trouble code when diagnosing a “check engine” warning light! Since the automatic transmission operation has a major effect on grams-per-mile exhaust emissions, you’re going to see the...

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Honda: Vehicle Won’t Move or Barely Moves

A customer brings in a vehicle that won’t move forward, ­­backward or both. Check first to see if it grinds or clicks. And does the speedometer read a lot higher than you’re actually going? Chances are the driveshaft is disengaged. This can...

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iATN Exceeds 2 Million Forum Messages

The number of messages in the professional automotive discussion forums of the International Automotive Technicians Network (iATN) exceeded 2 million in early December 2014, with the Shop Management and Technical Discussion forums being the most popular...

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Diagnosing Starter Misses

Contributing writer Gary Goms was called to a friend’s shop to help with a no-cranking condition on a 2006 Chevy Tahoe. After diagnosing a faulty PCM ground, locating the missing ground proved to be problematic. Find out how Gary solves The Case...

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Snap-on Adds Diagnostic Calculator To Website

Snap-on announces a new diagnostic calculator feature has been added to its website at http://diagnostics.snapon.com to help automotive repair technicians and shop owners determine how much profit they could be making by using a Snap-on diagnostic platform,...

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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]
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Oil-Related Engine Codes for VVT Engines

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TPMS Updates: From Reflashes to Refills

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Import Automatic Transmission Diagnostics

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SP Air Offers Super-Fast Mini Impact Ratchet

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