ASE G1 common mistakes
ASE G1 · Understand the traps and how to avoid them.
Using an ohmmeter on a live circuit, or judging a high-current cable or ground by resistance reading instead of doing a loaded voltage-drop test.
Early training drills 'check continuity/ohms' as the default electrical test, so the meter gets used on circuits that are powered or on cables where a fraction of an ohm is normal and meaningless at meter current.
What to do instead
Before every resistance test, key off and disconnect the component; for starters, grounds and battery cables, use a DVOM on the volts scale and measure drop while the circuit is loaded (target under 0.5 V per connection, under 0.2 V per cable).
Bleeding an ABS-equipped brake system by pedal pumping alone and never commanding an ABS bleed or cycling the pump, then releasing the vehicle with a spongy pedal.
Air trapped in the hydraulic control unit or accumulator cannot be pushed out through the wheel cylinders by pedal force, and the candidate assumes 'pedal is firm enough' or that the scan tool step is optional.
What to do instead
Follow the OEM sequence exactly: bench-bleed or prime the master cylinder, bleed wheels in the specified order, and perform the scan-tool ABS bleed/valve cycling procedure; keep the reservoir above minimum and recheck pedal height on a test drive.
Reading fuel trims as the fault rather than as the PCM's correction, and condemning an oxygen sensor or fuel pump because long-term trim is high positive.
The trim number looks like a measurement of mixture, so a lean-reading sensor or a vacuum leak both point at the same number; the candidate picks the part that is easiest to reach.
What to do instead
Interpret the trim as the direction of correction, then prove the cause: introduce propane or carb cleaner at suspect intake points and watch for a trim swing, check fuel pressure and volume under load, and compare upstream sensor switching before replacing anything.
Diagnosing a misfire as ignition and installing coils and plugs without ever running a compression or cylinder-balance test, then returning the vehicle still misfiring.
Ignition is the most familiar misfire cause and the misfire code names a cylinder, which feels like a diagnosis; compression and mechanical checks are skipped as time-consuming.
What to do instead
Do a relative compression or cranking compression check and a cylinder balance/power-balance test early, verify spark with a spark tester and injector pulse with a noid light, then move to ignition only after mechanical health is confirmed.
Charging an A/C system by gauge pressure alone to 'get the vent cold', without recovering and weighing the charge and without running a leak check.
Low-side pressure depends heavily on ambient and engine speed, so a partial charge can look close to spec on the manifold gauge set, and the customer only complains after the refrigerant leaks out again.
What to do instead
Recover, evacuate and recharge by weight to the underhood specification, add the specified oil amount, and confirm with an electronic or UV leak check plus vent-temperature and pressure-performance readings before releasing the vehicle.
Starting an alignment or setting toe without first inspecting ball joints, tie-rod ends, control-arm bushings and wheel bearings, and without checking tire pressures and ride height.
The alignment rack produces camber and toe numbers quickly, so the candidate adjusts to spec on a worn front end and the angles drift as soon as the vehicle is driven.
What to do instead
Perform a full pre-alignment inspection and shake test, correct tire pressures, check for accident damage and set the steering wheel and clock spring to center before measuring; replace worn parts and re-measure, and record thrust angle and setback.
Checking automatic transmission fluid level with the engine off and in Park, or on a vehicle that requires a specific fluid temperature and a scan-tool level check, then adding or draining fluid based on that reading.
The old dipstick-and-engine-off habit transfers from older units, while many late transmissions are checked with the engine running in a specific range, at a specified pan temperature, with a standpipe.
What to do instead
Look up the fluid level and fill procedure in service information first - engine state, gear range, fluid temperature window, and whether a scan tool or standpipe is required - then check, and top up with the exact specified fluid.
Testing a battery or alternator straight off a charger or after a jump start without removing surface charge, or load-testing a battery that is not fully charged and declaring it failed.
Surface charge holds voltage artificially high and an undercharged battery sags under load, so a healthy battery reads bad and a bad one reads good; these quick checks are done under time pressure.
What to do instead
Fully charge the battery, remove surface charge with a load or a few minutes of headlights, then test with a conductance tester and a load test; verify charging voltage and AC ripple at the battery with loads on and off before condemning the alternator.
Blaming a slipping clutch on a worn disc without checking release hydraulics, free play and adjustment, or topping off a limited-slip differential with ordinary gear oil and no friction modifier.
Clutch slip is automatically attributed to the friction disc, and differential fluid spec is treated as generic 'gear oil', when both faults present as symptoms the candidate has already seen once.
What to do instead
For a clutch, verify pedal free play, hydraulic release and fork travel, check for oil contamination at the bell housing, and measure disc and flywheel wear before removal; for differentials, use the specified fluid and add friction modifier when required for limited-slip units.
Doing a pad-only brake job: fitting new pads without measuring rotor thickness and runout against the discard spec, and installing pads without cleaning and lubricating the caliper slides with the correct high-temperature grease.
Pads are the visible worn part and pass inspection quickly, so rotor measurement and slide service are skipped; the result is noise, pulsation or a dragging caliper that comes back within weeks.
What to do instead
Measure every rotor with a micrometer and check runout and discard thickness against spec, machine or replace as required, service caliper slides and abutment clips with the specified lubricant, and verify with a road test and pedal check.