Inspection and Verification (Start Testing Here)

When it comes to today's electrically controlled RABS/4WABS, the diagnosis of many concerns requires following the diagnostic procedures exactly as they are outlined. But there is more to it than that. You have to take the information given you by the customer, and combine it with your understanding of brake systems in general. This knowledge and information will help you make the most efficient use of the diagnostic procedures in this manual.


Getting Started

Brake system diagnosis starts with the customer's complaint. It is best to get this information directly from the customer, not just from a service write-up. Customers usually do their best to describe what they have been experiencing and what their concerns are. But it is often necessary to ask questions and probe further in order to get a complete picture of the problem.

Customers may report that the brake pedal went to the floor, when it actually only dropped part way. Remember, customers get used to how their vehicle's brakes are performing. If the system suddenly behaves differently, they may become alarmed. Under these circumstances, what they report may not be as clearly stated as it could be. Your job is to listen carefully and ask probing questions about anything that doesn't fit your experience and understanding of brake system functioning.

Verify the Complaint

Once you are satisfied that you understand the customer's concerns, take the vehicle on the road yourself. Many brake concerns involve a wide variety of noises and pulsations that can only be experienced while operating the vehicle. Make sure the vehicle's tires are inflated properly. Make your brake application evaluation on level, dry, hard, smooth pavement that is free from oil, grease or loose dirt.

Back in the Shop

The next step in servicing a brake complaint is a thorough inspection of the system.

Brake Master Cylinder

Look for leaks. Clean the unit and remove the brake master cylinder filler cap. Check the fluid level. Check the condition of the gasket.

Hydraulic Leaks

On vehicles with power brakes, with the engine running, apply 667 N (150 lbs) force to the brake pedal and hold for ten seconds. If brake pedal height cannot be maintained for 10 seconds or the brake warning light comes On, service is required.

Occasional brake squeal can be caused by environmental conditions such as cold ambient temperatures, heat, rain, snow, salt, mud, hot ambient temperatures or high humidity. This occasional squeal is not a functional problem and does not indicate any loss in brake effectiveness.

Visually examine front and rear tires and wheel assemblies for damage such as uneven wear, tread washouts, or sidewall damage. Make sure the tires are of the same size, type and, where possible, same manufacturer. Any tire or wheel that is damaged should be replaced.

Wheels and tires must be cleared of any foreign matter, and tire pressures adjusted to the correct specification.

If tires exhibit uneven wear or feathering, the cause must be corrected. Check steering and suspension components for damage/wear and, if necessary, check and adjust steering alignment.