ASE B5 Mechanical & Electrical Components cheat sheet

Coolant path: water pump → engine block/cylinder heads → thermostat → radiator → water pump; heater core is a parallel branch from the engine outlet.

Thermostat rating is the opening temperature; stuck closed causes rapid overheating, stuck open causes slow warm-up and low heater output.

Pressure cap raises boiling point about 3°F per psi (1.7°C per 6.9 kPa); a 15-psi cap raises water boiling point near 257°F (125°C) at sea level.

Typical coolant mix is 50/50 antifreeze and water; freeze point and boiling point are checked with a hydrometer or refractometer.

Electric fan operation depends on coolant temperature, A/C request, and vehicle speed; no fan at high temperature or with A/C on indicates a fan, relay, or control fault.

A water pump weep hole leak indicates shaft seal failure; bearing growl or pulley wobble indicates bearing failure.

Trapped air causes overheating, gauge fluctuation, no heater output, and gurgling; bleed at high-point bleeder screws or with a funnel.

Combustion gases in coolant (bubbles, hydrocarbon test positive) indicate head gasket, cracked head, or cracked block.

Ohm's law: V = I × R; power: P = V × I. In series, current is common and voltage drops add; in parallel, voltage is common and current splits.

Battery at rest: about 12.6 V = 100% state of charge, 12.4 V = 75%, 12.2 V = 50%; recharge before load testing below 12.4 V.

Voltage drop is measured with the circuit loaded; excessive drop means resistance. Common limits: 0.5 V total high-current circuit, 0.1 V per connection.

Parasitic draw after modules sleep is typically 20-50 mA; higher draw discharges the battery. Measure with an ammeter or clamp.

Charging voltage is usually 13.5-14.5 V at the battery with engine running and loads on; AC ripple above about 0.5 V indicates diode failure.

Starter circuit includes battery, cables, ground, solenoid, and starter; test voltage drop on both positive and ground sides under cranking load.

Fuses protect circuits and must be replaced with the same rating; a blown fuse indicates an overload or short, not just a bad fuse.

Relay has a control coil and load contacts; coil opens or contacts burn. Test coil resistance and load voltage drop or substitute a known-good relay.

Hydraulic pressure = force ÷ area; a larger caliper piston area increases clamping force but requires more fluid volume and pedal travel.

Spongy pedal = air, leak, or master cylinder; low pedal = rear drum adjustment, leak, or air; pulsation = rotor runout or thickness variation.

DOT 3/4 glycol fluid is hygroscopic; moisture lowers boiling point and causes corrosion. DOT 5 silicone is not compatible with DOT 3/4 systems.

Replace disc brake pads when friction material is at or below 2/32 in (1.6 mm) or manufacturer specification.

Measure rotor thickness with a micrometer; replace if below stamped minimum. Check lateral runout with a dial indicator; excessive runout causes pulsation.

Bleeding order, unless specified, is farthest to nearest from master cylinder: RR, LR, RF, LF; keep reservoir full.

Parking brake systems include cable, lever, equalizer, and rear shoes or caliper actuator; dragging brakes can overheat and cause poor fuel economy.

ABS wheel speed sensor faults disable ABS and may turn on the brake warning lamp; scan tool data should show matching wheel speeds.

Caster is steering-axis tilt front-to-back; positive caster improves straight-line stability and return; excessive caster increases steering effort.

Camber is wheel tilt inward/outward; negative camber improves cornering but wears the inner tire edge.

Toe is the difference in distance between front and rear of tires; incorrect toe causes feathered wear and steering wheel off-center.

SAI and included angle help diagnose bent spindles or struts when camber or caster is out of range.

Check ball joints and tie rods with suspension loaded/unloaded per design; play causes wander, clunk, and uneven tire wear.

Wheel bearing noise usually changes with speed and may change when turning; check play and replace hub/bearing assembly.

Worn struts/shocks cause bouncing, tire cupping, and poor handling; inspect for leaks and mount wear.

Power steering hydraulic systems use pump, reservoir, lines, and rack; EPS uses motor and sensors; low assist can be fluid, belt, pump, or control fault.

Compressor → condenser → expansion valve/orifice tube → evaporator → accumulator/drier → compressor.

High side is hot and high pressure from compressor to expansion device; low side is cold and low pressure from evaporator to compressor.

Center vent temperature in a good system is typically 35-45°F (2-7°C) depending on ambient and humidity.

Refrigerant must be recovered and recharged by weight; never mix R-12 and R-134a; use correct oil and seals.

Orifice-tube systems use an accumulator on the low side; TXV systems use a receiver-drier on the high side.

Compressor clutch operation depends on pressure switches, PCM, and refrigerant charge; no engagement requires electrical and charge checks.

No heat with normal engine temperature indicates coolant flow, heater core, blend door, or air pocket; both heater hoses should be hot.

Four-stroke cycle: intake, compression, power, exhaust; two crankshaft revolutions per cycle; camshaft turns at half crank speed.

Timing belt/chain failure on an interference engine can bend valves; inspect interval and tensioner condition.

Engine vacuum at idle is typically 17-22 inHg at sea level; low or fluctuating vacuum can indicate leaks, timing, or mechanical fault.

Torque converter stall test compares maximum rpm at full throttle and held brakes to specification; low stall can indicate restricted converter or low engine power.

CV joint clicking on turns indicates outer joint wear; torn boots lose grease and admit contaminants.

Driveline vibration that changes with speed or acceleration can come from U-joints, CV shafts, tires, or mounts.

Automatic transmission fluid level is checked with engine running in park or neutral per manufacturer; low or burnt fluid causes slipping and harsh shifts.

SRS includes front/side airbags, pretensioners, impact sensors, clockspring, occupant classification, and control module.

Disable SRS by disconnecting battery negative and waiting manufacturer time, often 3-10 minutes, before working near modules.

Never probe airbag connectors with a multimeter or test light; use scan tool and follow service procedures to avoid deployment.

Clockspring provides continuity for driver airbag, horn, and steering wheel controls while the wheel turns.

Pretensioners use pyrotechnic charges to remove seatbelt slack and deploy with airbags; replace after deployment.

SRS lamp on means the module has set a fault and may disable deployment; retrieve codes before diagnosis.

Occupant classification system detects passenger weight and may disable passenger airbag; seat sensors and wiring faults set codes.