Four Wheel Logic

You can check car Freon levels by connecting an AC pressure gauge to the low-pressure service port while the engine runs and the air conditioner is set to

To check engine oil, pull the dipstick from a warm engine, wipe it clean, reinsert it fully, and remove it again to read the level between markers.

To check engine coolant, park on level ground, let the engine cool fully, then verify the fluid level sits between the “MIN” and “MAX” lines on the translucent

Locate the translucent plastic reservoir under the hood and verify the fluid sits between the “Min” and “Max” lines while the engine is cold.

To check compression on an engine, remove all spark plugs, disable the fuel and ignition systems, insert the gauge, and crank the engine for five pulses.

To check compression, warm the engine, disable the fuel system, remove all spark plugs, screw in the tester, and crank the engine to read PSI.

To check brake pads, look through the wheel spokes to see if the friction material is thinner than 1/4 inch (6mm) or listen for high-pitched squealing.

To check ball joints, lift the vehicle safely, grab the tire at the 12 and 6 o’clock positions, and rock it vertically to feel for clunking or excessive play.

To check an O2 sensor, back-probe the signal wires with a multimeter set to DC voltage and watch for rapid fluctuation between 0.1V and 0.9V while the engine

Set your multimeter to 20V DC, start the engine, and touch probes to the battery terminals; a reading of 13.5 to 14.5 volts confirms the unit works.