Auto Service World
Feature   November 1, 2001   by Dean Askin

The Essentials of ABS Service

There was a time when a doing brake job meant little more than raising the car, overhauling the drums and rotors, replacing calipers and pads if necessary. A few basic hand tools, some mechanical know...


There was a time when a doing brake job meant little more than raising the car, overhauling the drums and rotors, replacing calipers and pads if necessary. A few basic hand tools, some mechanical know-how, and presto, the job was done. Not so anymore. With ABS now ubiquitous on both domestic and import light vehicles and SUVs, modern brake repair and service is a complex task requiring specialized tools and knowledge that many technicians and shops can find daunting.

If you’re a dealership technician and work on only a few domestic or import models, ABS service and repair is perhaps a little less intimidating. You may have to know only one or a few of the many ABS systems on the market. Acura, or Jaguar XJ6 / XJS ABS systems, for example, on the import side. On the domestic side, you may have to know how to service only Bendix or Kelsey-Hayes systems.

For a general service shop, the task and need for knowledge grows exponentially. On any given day, the brake specialist could be called on to service Teves, Kelsey-Hayes, Bendix, Toyota, Acura, Delco-Moraine or a host of other ABS units. Moreover, you have to know the subtle differences between four-wheel and rear-wheel ABS systems; integral vs. non-integral systems; and how the procedures for servicing them differ.

Two essential tools

Consequently, the critical tools today are a scan tool – ideally a cartridge-based system with specific ABS troubleshooting and diagnostic capabilities – and either a paper-based comprehensive ABS troubleshooting manual that covers the basics of most systems on the market, or a software-based information system. The scan tool is essential for retrieving and clearing trouble codes, but it can’t fix the problem and tell you what to replace. For that, you need the scanner’s troubleshooter information, or the manual or software information system, to walk you through step-by-step diagnostics in a process of elimination to find and replace the faulty ABS component.

In addition, you’ll need to make sure your shop has specific service documentation from the various ABS manufacturers, since all systems are different. ABS component names, trouble codes, and diagnostic and brake-bleeding procedures vary from system to system. On Bendix ABS-4 systems, for example, a 2A trouble code reading covers 9 potential problems in the left & right front/rear solenoid circuits as well as the modulator circuit. Whereas Bosch 2U ABS sends individual two-digit trouble codes for each problem area – 44 for a Pilot Solenoid Valve Fault, 55 for a Left Rear Solenoid Valve Fault, for example.

A two-level task

Modern ABS service is actually a two-level task – the base brake system (calipers, rotors, drums, master cylinder, power assist, etc.), and the ABS system itself. The basic conventional brake tools you’ll need for the former; the diagnostic tools, knowledge and skills you’ll need for the latter part of the job.

Your brake specialist should definitely have these in his tool storage unit:

disc brake caliper set (with Hex & Torx drivers)

a general-service set (spring tools, bleeder wrenches, adjusting tools)

brake drum gauge, micrometer, brake rotor gauge

brake fluid safety test kit, to check moisture content

hose clamp pliers

brake tube bending pliers

brake caliper cleaning brush

ABS and brake pressure test kit

scan tool with an ABS troubleshooting cartridge

vacuum-type brake bleeder kit

When a customer comes into the shop and reports that he or she “hears a noise” in or “has a problem” with the brakes, the first tool you may be tempted to reach for is your scan tool. True, the diagnostics are important with ABS, but don’t dive in right away – the problem may lie elsewhere. A buzzing or rattling noise could be caused by check valve resonation in response to engine vacuum pulsations; clunking or pedal pulsations could be condition inherent in the design of the ABS and perfectly normal for the particular vehicle under certain braking conditions.

The first tool you should use is your eyes – do a complete, comprehensive visual inspection before you connect your scan tool to the Data Link Connector or Assembly Line Data Link. Check all of the following:

ABS system wiring harness connectors for looseness, especially the wheel sensor harness routing

Fuses in the instrument panel and under-hood fuse blocks

Brake fluid level in the master cylinder or reservoir

Integrity of fusible links

Parking brake switch for proper functioning

Grounds, to make sure they are clean and tight

Calipers, rotors, drums, pads, hoses, lines and master cylinder

Take it one step at a time – service the base brake system first, then the ABS portion. Service the rotors, drums, calipers, pads, hoses, master cylinder and lines; bleed the system; replace the brake fluid if you’ve tested it and the boiling point is below 170 C (338 F). When you’re bleeding brakes, remember – some ABS systems can be bled manually; others must be bled using your scan tool.

Also remember, a certain amount of caution and care is required – you don’t want to damage a sensitive wheel speed sensor while you’re doing wheel work; you need to follow proper bleeding procedures to avoid creating a new problem that causes an ABS warning light to come on and stay on. Also, don’t forget to disconnect the Supplemental Restraint System (SIR) before touching the ABS electronics – you don’t want an airbag to deploy.

The profitability factor

The very fact that ABS service is a two-level task also means that it can be a very profitable service to provide – if you do a complete brake job, as you should. In addition to replacing worn drums, rotors, calipers, pads and brake fluid in normal brake service maintenance, faulty ABS components must, because of their sophisticated electronics, be replaced. A rotor can be machined, but a wheel speed or later acceleration sensor can’t be repaired. If you’ve traditionally contracted out machining of rotors, consider investing in a fast, accurate brake lathe for your shop that can handle a wide variety of domestic and import rotors. Handling the machining in-house gives you more control over the brake work, and builds your profit potential for every brake job. Not to mention the productivity gains – you won’t have a bay tied up and a technician idle while you’re waiting on the machine shop.

Moreover, the very nature of ABS and its sensitive components offer you an opportunity to sell your customers on the need for regular, preventive maintenance. Many motorists don’t think about the ABS, because 99 per cent of the time, under normal braking conditions, the ABS doesn’t engage. So, many drivers mistakenly think that replacing shoes, pads, drums and rotors is all that there is to proper maintenance. Or they ignore the ABS warning light on the instrument panel. Neglecting the ABS – especially when an instrument panel light stays on – can lead to costly repairs down the road. Not such a great deal for the consumer, but a profitable situation for you. What all this means is that a $3,500 scan tool with an ABS troubleshooting cartridge can pay for itself quickly.

While ABS may at first seem daunting, and there’s a significant investment in tools and training required for modern ABS service, there’s a corresponding opportunity to build your bottom line with ABS repair and service. The availability of software-based diagnostic information systems, and sophisticated handheld diagnostic scan tools with specific ABS capabilities, mean there’s no reason for any shop to shy away from ABS service and repair.

Dean Askin is a Marketing Communications Specialist with Snap-on Tools of Canada Ltd.