Rick's Free Auto Repair Advice

Inspection checklist for used cars

Used car checklist — What to inspect when buying a used car

A used car inspection ALWAYS starts with a bulb check and scan tool review. Skip the exterior, undercarriage and road test until AFTER you’ve checked the computer

Bulb check

When you turn the key to the ON position, ALL dash warning

a bulb check is at the top of the list on every used car checklist

Different types of “Check Engine” lights

lights should come on, especially the “Check Engine or Service Engine Soon” light. This is referred to as the bulb check. Once you start the car, all the lights should turn off. Refer to the owner’s manual to identify all the warning lights. If the check engine or service engine soon lights don’t come on during the bulb check, the bulb has either burned our or have been disconnected. Until you know why the bulb isn’t lighting, you shouldn’t proceed with the inspection.

Scan tool inspection for trouble code and readiness monitor status

Connect the scan tool and check the readiness monitors

Readiness monitors

The computer conducts tests on the important emissions systems on a regular basis. As each system passes the test, it’s marked as “Ready”. If a system has failed the test, the computer will set a trouble code and set the readiness monitor for that system to “Not Ready.”

If ALL the readiness monitors show “Not Ready”, that’s a sign that the owner has recently cleared the trouble codes or disconnected the battery cables to wipe out recent codes.

If any of the readiness monitors are not set to ready, don’t buy the vehicle. Something is wrong. Until you know what the root cause is, don’t buy it.

Current Trouble Codes

A current code is one that’s stored has set, has not been fixed and is active. If there are current trouble codes showing up on your scan tool, get an estimate for diagnosis and repair from a local shop before negotiating the price

Pending Trouble Codes

These codes represent systems that have accumulated several failures, but haven’t yet reached the threshold of setting a current code. Follow the advice for Current trouble codes.

History Trouble Codes

These are codes that have been set and cleared. If the owner cleared the codes with a scan but the readiness monitors haven’t completed the testing, you’ll see the history code and a readiness monitor that’s “not ready.” However, if the owner cleared the codes by disconnecting the battery, that can sometimes delete the history codes. After reconnecting the battery cables, the computer would have to run all the readiness monitors from scratch.

Permanent Trouble Codes

A permanent code can’t be cleared by a scan tool or by disconnecting the battery cables. It must be diagnosed and repaired and the code must be cleared by the computer after completing a readiness test.

Scan tool test for live data when buying a used car

Short term fuel trim and long term fuel trim

When a vehicle leaves the factory, it runs on factory programming. As the vehicle wears in, the computer makes adjustments to the setting to compensate for engine wear. The two most important adjustments are short and long term fuel trims.

The computer will add or subtract fuel based on feedback from the oxygen sensors in the exhaust. The computer can add or subtract up to 25% fuel to short term fuel trim. If the computer has to add or subtract fuel for short term fuel trim for long periods of time, it moves the adjustment over to long term fuel trim.

Switch your scan tool to live data and examine short and long term fuel trim at idle and while driving.

Short term fuel trim will usually vary as you depress the pedal and release the gas pedal. It’s normal to see it swing from +10% to -10%. Under heavy acceleration it may occasionally rise to close to 25%, but it shouldn’t stay there. If long term fuel trim is higher than 10%, there’s a problem. The computer is being forced to add a lot of fuel. That can be a sign of a vacuum leak, misfires, a clogged fuel injector, or a weak fuel pump.

If the fuel trims are in the negative territory for long periods, that’s sign of a leaking fuel injector or high fuel pressure.

Oxygen sensor data

Pre-cat oxygen sensor data should vary rapidly. Post cat sensor data should be steady. If the post cat sensor vary at the same rate as the pre-cat sensors, chances are high that the cat converter is bad. That’s a very expensive part.

Those are the most important data points to examine using live data.

Mechanical checks when buying a used car

Cooling system

Check for worn out coolant

Using a digital multimeter, conduct an electrolysis test

coolant pH test strips and testing should be on your used car checklist shopping

Coolant pH test strips

using this procedure. If it passes the test, purchase a pack of coolant test strips and test the coolant for proper pH. If it fails either test, chances are high that the radiator or heater core have been compromised by corrosion.

Check for proper radiator operation

Using an infra-red thermometer, scan the surface of the radiator. Clogged fins will show up as cooler than the surrounding fins.

Check for proper thermostat operation

Using an infra-red thermometer, check the temperature of the

infra red thermometer

infra red thermometer

thermostat and compare to the area surrounding the thermostat. Then check against the engine coolant temperature sensor reading in the live data on your scan tool. The readings must match or be very close.

Check for coolant flow to determine proper water pump operation

If the radiator has a radiator cap, remove the cap when the engine is cold. The start it and let it run until the thermostat opens. Then look for coolant movement inside the radiator. Coolant movement that varies with engine RPM is a sign that the water pump is working properly.

Check the condition of all hoses for signs of rubber deterioration, soft spots, leaks, or sponginess.

Check the drive belt system

NOTE: Carmakers switched away from neoprene belts in the early 2000’s and started using EPDM belts. Neoprene belts cracked as they aged, EPDM belts don’t crack. The ribs wear down and the only way to measure the amount of wear is with a belt wear gauge.

Check drive belt wear with a wear gauge.

Check the drive belt tensioner

If the vehicle is equipped with an automatic belt tensioner, rotate the tensioner. It should move smoothly without any binding. It should not make any noise. It should not show and rust. If it passes those tests, refer to this post to see how to check belt tensioner movement while the engine is running.

Check the idler rollers

Using an automotive stethoscope, remove the metal probe and use the open tubing to listen at each idler bearing for an grinding noise that might indicate a worn bearing.

Check the battery and charging system

Using a multimeter, check battery voltage. Use the battery/temperature chart in this post to determine battery voltage based on battery temperature.

Using a battery tester, perform a full battery test to see if it passes.

checking the battery is on every used car checklist

Solar BA9 battery tester

With the multimeter connected to the battery, start the vehicle and keep it at 1,500 RPM. Battery voltage should be above 13.5 volts. Turn on the headlights, rear window defogger, heated seats, heated mirrors and blower motor on high. Boost RPMS to 2,000. Battery voltage should not fall below 13.5 volts.

Visual engine checks

Check for any signs of oil leakage

Examine around the valve cover gasket for oil leaks

Examine around the head gasket for oil leaks

On overhead cam engines, remove the ignition coils and check for oil accumulation in the spark plug wells. That’s an indication of a failed spark plug tube seals.

With the spark plug wires/ignition coils removed, check for signs of arcing or coil cracks or deterioration.

Remove spark plugs and check for gap, electrode erosion or electrode damage. A missing side electrode or cracked insulator is a sign of detonation.

Exterior visual inspection

Tire Inspection

Using a tire tread depth gauge, measure the tread depth in the used car checklist. This shows how to measure tire tread depthmiddle and inner and outer edges. They should all be within 1/32” of each other. More wear indicates an alignment issue.

Run your hand around the tire and check for divots/cupping. That would indicate worn struts/shocks.

Check the manufacturing date or the tires. Tires are good for 6-years from the date of manufacture and must be discarded after 10 years from the data of manufacture.

Check for cracks, bubbles in the sidewall or between tread blocks. Cracking is a sign of overheating and rubber degradation.

Tires should all be the same brand and model and front and all tire tread should be within 2/32” of each other. This is even more important fi the vehicle is an AWD or 4WD.

Check the age and condition of the spare tire.

If the spare tire is located under the vehicle, lower it to check the operation of the tire lift. Make sure the tire lift tools, jack and tire iron are all included.

TPMS inspection

The TPMS light should come on when doing the bulb check and should turn off once the engine is running.

Windshield and wiper check

Check the windshield for chips or cracks. Check for signs of previous repairs.

Check the condition of the windshield wipers by conducting a wash operation. The wipers should remove the water without leaving any streaks. If you see streaks, the wipers are worn.

The wiper arms should move freely and smoothly without making any noise. Noise or jerky movement is an indication of worn wiper linkage.

Perform the same check on the rear wiper if equipped.

Check door, hood, and trunk/hatch operation

Using the key, lock and unlock the doors and trunk/hatch to confirm the locks work smoothly.

Open and close each door to confirm they open/close from the inside and outside. The latching should be smooth without any need to slam the door. The hinges should not make noise. The door “stays” should keep the doors open when you let go.

Check for wear marks on the strike in the door jamb. Wear is an indication of a door out of alignment due to a worn hinge.

Check door, trunk, hatch weather stripper for tears and degradation.

Operate each window to make sure the window buttons work and the window moves up and down smoothly.

Visual check of lights

Check the operation of the headlights: high and low beams. Check to see if the owner has retrofitted the headlights with LED or HID bulbs. If so, you’ll want to remove those and replace with the recommended bulbs

Check the operation of the turn signals, backup lights, hazards, parking and stop lights.

HVAC checks

Check AC operation

Using a dial thermometer placed in the center dash duct, set the AC to MAX and blower to HIGH. Close the windows and turn the system to recirculate. Start the engine and let the AC run. The temperature in the center dash duct must be below 40°F and as close to 34° as possible. (Although it depends on the outside air temperature and humidity when conducting this test.)

Check mode and blend door operation.

Change the heat setting and confirm that the air temperature changes on both sides of the vehicle as you do this.

Change the modes from floor to dash to defrost. Confirm that the air flow changes with each selection.

Remove the cabin air filter and check its condition.

Pop the hood and touch the inlet and outlet hoses to the heater core. They should be hot after the engine has been running.

Check seat condition and operation

Check the seats from signs of wear. Check the seat track and power seat options to ensure they operate properly.

Radio check

Listen to radio to check for static, crackling or the signs of blown speakers.

Exterior body checks

Check for color mismatches on the fenders, doors, hood and rocker panels that would indicate previous body damage and repairs

Check for paint over spray in wheel well areas that would indicate previous body repairs

Check for paint smoothness, orange peel or rough spots.

Check the bottom of each door for signs of rust

Check suspension

Test shocks for wear by conducting a bounce test. See this post for the test

Test struts with a drive test. (the bounce test is not a valid test for struts)

Perform a visual inspection of the struts/shocks, springs and strut boots.

Check the control arm bushings for wear and cracking.

Support the vehicle on jack stands and check for wheel bearing play.

Check for slop in the steering linkage.

Check the transmission visually

Perform a visual inspection of the transmission, looking for leaks. Transmission leaks can be costly to repair.

Check the drive axles

Inspect the CV boots for signs of leakage or tearing

torn CV boot

Torn inner CV boot. Notice the grease has leaked out













Check the steering gear or rack and pinion for signs of leaking fluid

leaking power steering rack


Check the brakes for signs of wear

Remove the wheels and calipers to check the condition of the brake pads. Measure the pad thickness. Check the condition of the rotors. Check the movement of the caliper slide pins. Check the condition and operation of the parking brakes and cable.

brakes make grinding noise

Brake pad backing plate has rusted. “Rust jacking” (expanding rust) causes the friction material to debond from the backing plate. The friction material cracks, causing uneven friction material to rotor application which causes a grinding noise

Check the brake fluid for moisture and copper

Brake fluid accumulates moisture. More than 4% can cause braking issues as the water boils. Water in the brake fluid also facilitates corrosion.

All brake fluid contains anti-corrosive additives. When those additives wear out, the water in the fluid attacks the brake lines and shows up as copper in the fluid. Use a brake fluid test strip to determine the condition of the brake fluid.

Check the undercarriage and frame

With the vehicle on a lift, check for signs of rust perforation on major support components.

rusted control arm

Rusted control arm

Rusted structural component

Rusted structural component

image of multiple rusted brake lines

Rusted brake lines

rusted brake lines

Rusted fuel lines

Rusted fuel filter and fuel lines

Rusted fuel filter and fuel lines

Perform a road test

Before the road test, check the oil for proper level. Check coolant level and check brake fluid and power steering fluid levels.

Start the engine cold

It should start without extended cranking. It should idle high and then drop down to a normal idle after a short time. The idle should be steady without any rise/fall (called “hunting”).

Listen for squeaks, chirps, grinding or knocking sounds.

These all indicate a problem that must be diagnosed before buying the vehicle.

Shift into Drive

The transmission should engage into drive smoothly and without hesitation.

Pay attention to the shift points

All transmissions are different, but with gentle acceleration you should feel the 1-2 shift at about 15-mph, the 2-3 shift at around 25-mph, and it should go into overdrive at around 40-mph.

The shift should be smooth with no clunking. If should go into Drive and Reverse smoothly, again with no clunking and no delay.

The shifts should be smooth without any banging

Pay attention to the steering and suspension

The steering should be solid. If there’s play in the wheel, there are worn parts that cost a lot of dough.

The front end should not dip when stopping. If it does, that’s a sign of worn shocks/struts

The vehicle should not pull right or left.

Let go of the wheel on flat pavement to see if it continue to drive straight. It’ll eventually move, but it shouldn’t go to one side immediately.

It should stay in it’s own lane on bumpy roads.

Wander is a sign of worn steering and or struts/shocks.

The brakes should stop the vehicle without any pulsation or noise.
Set the cruise control and see if it maintains the proper speed.

Check ADAS system

If the vehicle is equipped with Advanced driver-assistance systems, check their operation.

Operate all accessories

Test the power seats and heated seats
Test the side mirrors, backup camera, GPS/Navigation systems

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