Three general trends characterize ABS service, brake professionals said. First, the root cause of the customer's complaint is as likely to be in the basic brakes as in the ABS system itself. Second, typical ABS failures and the required repairs are fairly straightforward. Unfortunately, ignorance of the ABS system at hand often turns a simple fix into a difficult situation.
Third, ABS doesn't tolerate the careless work habits and shortcut procedures older, simpler brake systems did. For example, a common shortcut can ruin a $1,000 ABS actuator assembly!
Check basics first
Dave Hayes is service manager and general manager of Stan's Tire & Auto Service Center, Lafayette, Colo. Mr. Hayes said that in addition to doing its own ABS diagnosis and repairs, his dealership is getting ABS jobs other shops are turning away.
He emphasized that a thorough inspection of the conventional brake system is as important to quick, accurate ABS diagnosis as it is to troubleshooting conventional brakes.
``We notice a tendency for people to blame the ABS computer. But we learned we don't know where we stand until we inspect the entire brake system first,'' Mr. Hayes said.
Some tire dealerships and service shops generate service sales via comprehensive vehicle inspections. According to Jeff Smith, service manager at Smitty's Alignment Service in Doylestown, Ohio, ABS is making vehicle inspections more important than ever before. He's encountered a number of cases where burned-out brake light bulbs disabled an ABS system.
Mr. Smith said many techs know that bulb failure will trigger a dashboard or console display on vehicles equipped with safety monitoring systems. But few realize that bulb failure can also disable ABS and/or cruise control systems!
What's more, some techs overlook the fact that both the ABS light and the standard brake system warning light are illuminated. An
illuminated brake warning light should prompt techs to inspect the basic brake system first, Mr. Smith added.
Ned Lineback, a technical trainer at Wagner Brake Products, reminded technicians that an ABS system cannot overcome problems in the conventional brake system.
A good example is a deteriorated brake hose that ``check valves'' the brake circuit.
This occurs when part of thehose's inner lining flakes off, restricting the hose.
``Hose failures like this can restrict brake fluid going to the brake. They also can trap fluid at the brake so the brake won't release or won't release completely,'' he said.
If wheel lock-up persists during a panic stop, the ABS system tries to unlock the wheel by releasing brake application pressure. But if a partial hose restriction prevents a brake from releasing completely, the ABS may not be able to unlock a wheel during an emergency stop, Mr. Lineback said.
When in doubt, technicians should road test a vehicle thoroughly and check for dragging brakes after the road test. Then see if correcting the dragging brake condition clears up the ABS trouble.
Understand ABS operation
Sources said they often see easy ABS diagnoses bungled because the technician knows nothing about the basic operation of the system. Therefore, the tech has no idea what normal system operation should be.
For example, many vehicles are equipped with integral ABS designs in which the master cylinder and electrical-hydraulic (EH) actuator are integrated into one assembly.
Instead of using the familiar vacuum-operated power brake booster, a pressurized accumulator provides the power assist. When accumulator pressure drops too low, a pressure switch activates a pump that replenishes the accumulator. Technicians familiar with integral ABS recognize the distinctive buzzing sound this pump makes.
If the pump fails to replenish the accumulator for any reason, the driver reports the same symptom he noticed when a vacuum brake booster failed-a hard brake pedal and excessive pedal effort required to stop the vehicle.
At Smitty's Alignment, Mr. Smith recalled an instance in which an integral ABS-equipped Thunderbird came in from another shop with these symptoms.
When these symptoms occur on a conventional brake system, he said, a capable technician instinctively suspects a power booster failure. Likewise, a good tech should suspect a power assist problem when the brake pedal is rock hard, the driver must apply the brakes with both feet to stop the car and he doesn't hear the ABS' pressure pump buzzing when he turns on the ignition switch.
A quick voltage check on the Thunderbird revealed that no power was reaching the pressure pump. Several additional voltage tests confirmed the relay controlling the pressure pump had failed. So within minutes, this ABS ``mystery'' was accurately diagnosed and repaired, Mr. Smith said.
Jeff Masterman, a technical trainerfor Standard Motor Products and its
EIS Brake Parts division, said many techs don't understand the integral ABS accumulator does more than provide power assist-it also applies the rear brakes.
``There's no `manual override' here,'' he explained. So the ABS pump must run and the accumulator must be pressurized in order to apply and/or bleed the rear brakes.
Ford Motor Co. specialists said ignition switch failures-including intermittent ones-are commonplace on some Ford products. As a result, Ford upgraded the ignition switch on cars such as Lincoln-Mercury's Continental.
Mr. Masterman said he's seen uninformed technicians battle double trouble on cars such as the Continental. First, they can't bleed the rear brakes because the ABS pump isn't running and the accumulator's depleted. Second, when they do try to operate the ABS pump, the pump runs intermittently because the ignition switch is failing.
Creating new problems
Brake experts agreed that careless work habits continue to raise havoc during ABS diagnosis and service. The most common and flagrant mistake is retracting caliper pistons without opening the caliper bleeder fitting first.
Sources urged technicians to always open the bleeder fitting before pushing in a caliper piston-even on routine ``hang-and-turn'' brake jobs. Here's why ignoring this simple step can cause your service shop some very costly comebacks.
Opening the bleeder fitting beforehand vents old brake fluid from the caliper when the tech pushes back the caliper piston prior to disc pad replacement. If he doesn't open the bleeder fitting and vent the old fluid, the caliper piston may force dirty fluid back into the ABS system's EH actuator, ruining it.
``People forget that on an ABS brake system, the very next component upstream from the caliper is the EH actuator and that's right where the dirt goes,'' Mr. Masterman said.
Elsewhere in this service section, a procedure for flushing dirt from a rear-wheel ABS EH actuator is described. However, experts said the design of many EH actuators makes it impractical or impossible to effectively flush them.
On the Kelsey-Hayes rear-wheel ABS, a dirty EH actuator usually causes a low, spongy brake pedal. Typically, this relatively simple actuator costs less than $150.
Forcing dirty fluid into a more-sophisticated, four-wheel ABS actuator may disable the ABS and trigger trouble codes. For example, contaminating the Kelsey Hayes four-wheel ABS actuator can trigger trouble codes 61, 62, and 63, said Tom Amundson, technical instructor at Raybestos/Brake Parts Inc.
A careless, uninformed technician performs what he thinks is a routine disc pad replacement, only to have the vehicle come back with the ABS light illuminated, a ruined EH actuator and an extremely upset customer, Mr. Amundson said.
EH actuators for four-wheel ABS systems can cost from $1,000 to $1,500.