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Ford: Smoke From Vehicle When Starting

Vehicle: 2005 Ford Taurus SE, 3.0L Complaint: The customer says smoke comes from vehicle when starting. Cause: Confirmed the customer’s complaint and found smoke coming from the vehicle when the engine was started. Inspected the vehicle and found...

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R-1234yf Safety Procedure Checklist

Remember that R-1234yf is only mildly flammable. To become flammable, the mixture of air and refrigerant in a closed area like a vehicle cabin would need to be between 6.5% and 12.3% of the chemical vapor. This mixture must then experience a significant...

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Refrigerant Revolution: What R-1234yf Means for Service, Equipment, Safety

The new R-1234yf refrigerant is more than just a new jumble of numbers and letters on a label. For your shop, R-1234yf means several new procedures, a certification and new equipment in order to properly handle these new systems. Why the difference...

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Weak Air Ride Compressor Diagnostics

Air ride systems always used to have two diagnostic paths: either the vehicle was riding low or the compressor blew a fuse. Today’s modern vehicles have computer-controlled air ride units at all four corners that can pose a unique diagnostic challenge...

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Ford Fusion Alignment Spec (2005-‘13)

Millions of Ford ­Fusions were sold in the U.S. between 2005 and 2013. When it comes to alignments, it is critical to diagnose the customer first, to find out if their Fusion drifts or pulls, and then to check all of the possibilities for the complaint...

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Nissan Titan Brake Job

The Titan is Nissan’s full-size pickup. The Titan has had no major brake problems or recalls, and the brakes are fairly easy to service. Nissan had a few teething problems with brake judder on 2004-‘06 models, but this was corrected with better...

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Engine Coolant Temperature Diagnostics

While old-school cooling system service often ­focused on coolant leaks and overheating engines, let’s begin thinking “new-school” by looking at modern cooling systems through the eyes of the engine coolant temperature (ECT) sensor. Coolant temperature...

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Volkswagen: Parking Indicator Sounds Off with No Obstacle

Customer complains that the parking assistance issues warning sounds for both the front and/or rear of vehicle with no obstacle in range. Water intrusion into sensor holders is causing corroded plug contacts and sensor electrical pins, which results in...

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Volkswagen: Unnecessary Electric Coolant Fan Replacements

Model: 2006 Volkswagen Jetta Sedan Customer concerns of “electric coolant fans continue to run after the ignition is switched off” are resulting in unnecessary coolant fan replacements. It is considered normal operation for the electric coolant...

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Educating Drivers, Technicians and Service Advisers with Dill’s New TPMS Videos

Dill Air Controls has launched its new TPMS training and educational videos, supporting three audiences — consumers, technicians and service advisers. The consumer videos are available in shortened versions, and are positioned for the customer waiting...

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Top 5 Tools: Kenny Younkins, Ken’s Auto Service Center

Kenny Younkins, owner Ken’s Auto Service Center Akron, OH While Ken first said his favorite tool is his fishing rod, he said in the shop he prefers these five:   Snap-on 3/8” Drive Impact Wrench Mastercool Brake Flaring Kit Mitchell...

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Mitchell 1 Enhances Quick Links and Printing Functions in Latest Release of ProDemand

Mitchell 1 announces it has made several important enhancements in the latest release of its ProDemand repair, diagnostic and maintenance information program as a direct response to customer feedback. The implemented changes include an expanded Quick...

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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 amarkel@babcox.com.
Latest articles from our other sites:

Ford: Smoke From Vehicle When Starting

Vehicle: 2005 Ford Taurus SE, 3.0L Complaint: The customer says smoke comes from vehicle when starting. Cause: Confirmed the customer’s complaint and found smoke coming from the vehicle when the...More

R-1234yf Safety Procedure Checklist

Remember that R-1234yf is only mildly flammable. To become flammable, the mixture of air and refrigerant in a closed area like a vehicle cabin would need to be between 6.5% and 12.3% of the chemical vapor....More

Weak Air Ride Compressor Diagnostics

Air ride systems always used to have two diagnostic paths: either the vehicle was riding low or the compressor blew a fuse. Today’s modern vehicles have computer-controlled air ride units at all four...More

Diagnostic Strategies For Solving TPMS Errors

The first step in any diagnostic strategy is to figure out whether or not your customer's vehicle actually has a TPMS problem. Any number of things can cause the TPMS warning light to come on or flash....More

Engine Coolant Temperature Diagnostics

While old-school cooling system service often ­focused on coolant leaks and overheating engines, let’s begin thinking “new-school” by looking at modern cooling systems through the eyes of the engine...More

Volkswagen: Parking Indicator Sounds Off with No Obstacle

Customer complains that the parking assistance issues warning sounds for both the front and/or rear of vehicle with no obstacle in range. Water intrusion into sensor holders is causing corroded plug contacts...More

Coats’ Double-Sided Collets Capable of Fitting Most Car and Light Truck Wheels

As opposed to standard cones, the design provides technicians with a durable and precise mounting method, replicating the mounting of the wheel on the vehicle. When back coning, the shallow depth and...More

Clore Offers Redesigned Digital Battery & System Tester with Integrated Printer

Newly redesigned, the SOLAR BA327 from Clore Automotive offers a complete testing solution for 6- and 12-volt batteries and 12- and 24-volt charging systems. The tester’s integrated printer provides...More