The top 12 service checks :

CHECK #1: FLUID LEVELS
Check the oil, coolant, transmission fluid, power steering fluid, brake fluid and windshield washer reservoir. Top off as needed if any levels are low. Most importantly, find out why the level is low. A low fluid level often indicates a leak. With brake fluid, this can create a dangerous situation because fluid loss can lead to brake failure. So always inspect the brake system for leaks if the fluid level in the master cylinder reservoir is unusually low.

A low oil level may mean the engine is burning or leaking oil. If a visual inspection revels no leaky gaskets, a compression check might be recommended to check the condition of the rings. If compression is still good, it means the oil is being sucked down the valve guides.

A low coolant level can lead to rapid overheating, and often indicates a coolant leak. Check the hoses, radiator, freeze plugs and heater core for signs of leakage. No leaks? Then pressure test the cooling system and radiator cap. Internal leakage is bad news for your customer because it means the head gasket is leaking or the head or block are cracked. A cap that doesn't hold its rated pressure can allow coolant to escape from the system. A weak cap (or the wrong one for the application) will also lower the boiling temperature of the coolant, increasing the risk of a boil-over during hot weather.

If power steering fluid is low, check the hoses and steering rack. Squeeze the bellows on both ends of the rack to see if there's fluid inside. A little fluid is normal, but a lot of fluid would tell you the rack's internal seals are leaking and that the rack will need to be replaced.

Low transmission fluid would signal a leaky seal. On a rear-wheel drive car, truck or SUV, check the driveshaft seal in the tailshaft. On a front-wheel drive car or minivan, check the halfshaft seals on the transaxle. Leaky seals should be replaced because excessive loss of transmission fluid can lead to transmission slipping, overheating and failure. Another source of fluid loss can be the transmission fluid cooler in the radiator. Cross-contamination between transmission fluid and coolant can doom a transmission to premature failure.

CHECK #2: BRAKE FLUID CONDITION
Here's a check that's often overlooked if the fluid level appears to be normal. This requires the use of an electronic fluid tester or chemical test strips that react to water content in the fluid. If the fluid is badly contaminated with water (which most brake fluid is after several years of service), recommend a fluid change to restore the fluid's boiling resistance and corrosion protection.

CHECK #3: TIRE INFLATION PRESSURE
All four tires should be inflated to within a couple of pounds of the vehicle manufacturer's recommended inflation pressures for the front and rear tire (see the decal on the door jam, in the glove box or owner´s manual). And don't forget to check the spare tire, too.

If a tire is low, visually inspect it for nails, pinholes or blisters. Also check the valve to see if it is leaking air. If the problem is a rim leak or porosity leak through an alloy wheel, the tire may have to be dismounted to make repairs.

CHECK #4: TIRE CONDITION
Tread wear is a great indicator of wheel misalignment as well as worn and damaged steering and suspension parts. A feathered wear pattern or shoulder wear on both front tires can result from toe misalignment. Heavy inner or outer shoulder wear on only one tire would point to camber misalignment. Rear tires on front-wheel drive vehicles can often develop a saw tooth wear pattern if rear toe is off, or the tires have never been rotated.

CHECK #5: BRAKE PEDAL FEEL
Start the engine and step on the brake pedal. It should feel firm and travel no more than an inch or two before the brakes are fully applied. If the pedal feels soft, sinks while you're maintaining steady pressure on it, or travels too far down before applying the brakes, it indicates a need for additional checks and possible brake repairs.

A soft pedal would tell you there's air in the system. It could be a caliper, wheel cylinder or brake line. Or, if the master cylinder has run low because of a fluid leak somewhere in the system or badly worn linings, air could be in the master cylinder or ABS modulator.

The only way to get air out of the system is to bleed all four brake lines following the vehicle manufacturer's recommended bleeding sequence. But even that won't do the trick if air has found its way into an ABS modulator. Some ABS modulators have bleeder valves to vent trapped air while others require the use of a scan tool to cycle the ABS solenoids to get the air out. Either way, the fix will take some time and may require bleeding all four brake lines a second time to assure a complete purge and a firm brake pedal.

A low pedal can be another symptom of air in the system, but can also be the result of worn linings or frozen drum self-adjusters. Don't bleed the brake lines until you've inspected both the front and rear brake linings. Chances are you'll find the rear drums are not self-adjusting. A simple adjustment to tighten up the shoes may temporarily restore normal pedal travel, but as the miles accumulate the pedal will slowly lose height if the self-adjusters are not doing their job. The fix here is to pull the drums, clean and lubricate the self-adjusters, or replace them if they're too badly corroded to work reliably.

A pedal that slowly sinks under pressure is a classic symptom of a bad master cylinder. It means fluid pressure is leaking past the piston seals. This is a dangerous condition and requires replacing the master cylinder.

If possible, test drive the vehicle and note how the brakes behave under various braking conditions. Do a couple of panic stops to see if there's any pull, or if the brakes lockup. If the vehicle has antilock brakes, the ABS system should prevent the latter from occurring. Also note if the ABS or brake warning light comes on when the brakes are applied. A warning light would tell you further diagnosis is needed.

CHECK #6: FRONT DISC BRAKE PAD THICKNESS
Regardless of how the brakes feel or perform, you should always measure the thickness of the front disc brake pads to make sure they are still within the vehicle manufacturer's specifications. Thin linings can be dangerous linings because they reduce the brake systems' ability to manage heat. Excessive wear on riveted pads also increases the risk of rotor damage or even lining breakage or separation from the backing plate. If the pads are worn down to minimum specifications or less, replacement is required for save driving.

CHECK #7: FRONT DISC BRAKE ROTOR CONDITION
Brake rotors should be reasonably smooth (some light grooving is normal) and free from cracks or heavy discoloration. There's no need to measure rotor thickness unless there's a pedal pulsation when the brakes are applied (indicating warped rotors) or the linings are worn. If new linings are needed, always measure the thickness of the rotors to make sure they are above minimum or discard specifications. If the rotors have to be resurfaced, make sure there's enough meat left in them to safely do so — otherwise new rotors are needed. Thin rotors are dangerous rotors because they can't absorb and dissipate heat as well, and are at increased risk of breakage. If you find cracks in the rotors, they must be replaced. Resurfacing warped rotors is probably a waste of time because hard spots often extend beneath the surface and will eventually return causing pedal pulsations to return.

CHECK #8: PARKING BRAKE
Though many people hardly ever use it, the parking brake is nonetheless a safety item and should be checked to make sure it works and is capable of holding the vehicle. On cars with four-wheel disc brakes, the locking mechanisms in the rear calipers are often frozen and totally useless. Those with "mini-drums" inside the rear rotors are less troublesome.

CHECK #9: REAR DRUM BRAKES
This is one check you don't have to do unless brake pedal travel is excessive, the rear brakes are making noise or dragging, or you find the front brake pads are worn. The rear brakes always last longer than the front brakes because they don't work as hard. Even so, they do eventually wear out and have to be relined. Checks here would include measuring the thickness of the linings on the shoes (replace if they are at or below minimum specifications) lining condition (replace if cracked, flaking, damaged or contaminated with brake fluid or grease), and the inside diameter of the drum (replace if it exceeds maximum specifications).

CHECK #10: STEERING PLAY, FEEL & RETURN
On most vehicles, there should be little (less than 1/4 inch) or no play in the steering wheel. Loose steering may indicate worn tie rod ends, a worn idler arm, wear or maladjustment in the steering gear, or a worn steering column coupling. Any of these conditions are potentially dangerous because a failure anywhere in the linkage or gear would result in loss of steering control.

Steering feel and return can only be checked by test driving the vehicle. Stiff steering or poor return may indicate a loss of power assist or binding in the linkage, ball joints or upper strut bearing plates. Steering wander can be caused by a worn idler arm, tie rod ends, loose wheel bearings or worn or broken rack mounts. Further checks would be required if any problems are noted.

CHECK #11: RIDE & HANDLING
This also requires a short test drive. How a vehicle handles bumps and curves will tell you if the shocks, springs, struts or sway bar bushings need attention. Any seesaw motion after hitting a bump, excessive nose dive when braking or body sway when cornering would tell you the dampers are weak and may need to be replaced or upgraded.

If you customer uses his vehicle for towing (check for a trailer hitch), ask him what he tows. Unusually heavy trailers may require beefing up the suspension (installing variable rate, overload or helper springs), better shocks and an auxiliary transmission fluid cooler to protect the automatic transmission against overheating.

CHECK #12: EXHAUST NOISE
Listen for any noise that might indicate an exhaust leak (hiss, whistle, rumble or roar). Exhaust leaks can be both annoying and deadly. Although most people worry more about the dangers of carbon monoxide poisoning during cold weather when windows are up and vehicles may be left idling to warm up, they should also worry about the risk during hot weather too when windows are up and the air conditioning is on.

If you hear any leaks, inspect the entire exhaust system from engine to tailpipe.

Another check that might be needed here is to check for excessive back pressure if the engine seems sluggish or unresponsive. A partially plugged converter, crushed pipe or collapsed inner lining in a double-walled pipe can create a restriction that causes back pressure to build up. The quickest check for this condition is to read intake vacuum with the engine idling. A lower than normal reading that continues to drop would indicate an exhaust restriction.