ASE A6 cheat sheet

Ohm's law: E = I x R; power P = I x E = I^2R = E^2/R. Use it to predict current from measured voltage and resistance.

Voltage drop tests are made with the circuit energized and current flowing; the voltmeter connects in parallel across the cable, connection, or switch under test.

Typical maximum voltage drops at full load: 0.5 V over a cable run, 0.1 V per terminal or connection, 0.3 V across a switch, 0.1 V per ground-side connection.

Series circuit: one current path, current identical through every element, resistances add, and the individual voltage drops sum to source voltage.

Parallel circuit: voltage identical across every branch, branch currents add to total current, and total resistance is less than the smallest branch resistance.

Resistance measurements require the component isolated and the circuit de-energized; a reading taken through a parallel path is falsely low.

Parasitic draw specification is usually 20-50 mA after all modules sleep (often 20-60 minutes); measure with a low-amp clamp or an ammeter in series with the negative cable.

Relay terminals: 85 and 86 are the coil, 30 is the battery feed, 87 is the normally open load contact, 87a is the normally closed contact.

Intermittent faults are captured with a DMM in min/max record mode or a lab scope while harnesses are wiggled and components are heated or cooled.

Open-circuit voltage at 25 degrees C after surface charge removal: 12.66 V = 100%, 12.45 V = 75%, 12.24 V = 50%, 12.06 V = 25%, 11.90 V = 0%.

Load test: apply one-half the rated CCA for 15 seconds; the battery must hold at least 9.6 V at 21 degrees C (70 degrees F).

Three-minute charge test: charge at 30-40 A for three minutes; a rise above 15.5 V indicates high internal resistance or sulfation and the battery is replaced.

Temperature-corrected specific gravity on a flooded battery: 1.265 = full, 1.225 = 50%, 1.190 = 25%, 1.120 = discharged.

A 12-volt battery has six cells at about 2.1 V each; a cell-to-cell variation of roughly 0.05 in specific gravity or 2 V under load identifies a bad cell.

AGM batteries take a lower absorption voltage than flooded batteries and are not equalized; the charger must be set to the chemistry of the battery installed.

Never charge a frozen battery, or one whose electrolyte level exposes the plates; both create an explosion hazard.

A memory saver preserves radio, clock, and adaptive settings during battery replacement; some vehicles still require an idle or steering-angle relearn afterward.

Terminal clamp torque and hold-down integrity matter: a loose battery can crack internally and a loose clamp adds cranking voltage drop.

Normal cranking voltage at the battery is 9.6 V minimum at 20 degrees C; a lower reading during crank points to state of charge, cables, grounds, or starter draw.

Typical starter current draw is 150-250 A; much higher draw suggests a seized engine, a shorted starter, or excessive cable resistance.

Cranking voltage drop limits: 0.5 V maximum on the insulated B+ cable and 0.2-0.3 V maximum on the ground side.

Solenoid terminals: B is battery positive, S is the start signal from the ignition switch, M feeds the starter motor; the S terminal is used for remote cranking.

No-crank diagnostic order: battery state of charge, terminal condition, grounds, fusible links, ignition switch, neutral safety or clutch switch, relay, solenoid, starter.

Automatics crank only in Park or Neutral; a misadjusted or faulty neutral safety switch produces a no-crank with normal headlamp brightness.

Starter spins but the engine does not crank: inspect the drive or Bendix, overrunning clutch, flywheel ring gear, and starter mounting.

Bench testing compares free-running current and rpm at a specified voltage to the manufacturer specification, not to another used starter.

A remote starter switch connected between battery positive and the S terminal bypasses the control circuit to separate a control-side fault from a starter fault.

Charging voltage is typically 13.5-14.8 V at 2000 rpm with accessories off and 12.6-13.5 V with a full electrical load applied.

System voltage above about 15.5 V indicates regulator failure or an open voltage-sense circuit and will boil and overcharge the battery.

Diode ripple test: DMM set to AC volts across the battery; more than about 0.5 V AC indicates a failed rectifier diode.

The regulator needs battery voltage on the sense wire and initial excitation through the charge lamp or I terminal; a burned-out charge bulb can stop charging on some designs.

Voltage drop on the alternator B+ output cable must be less than 0.5 V at full output; higher means a bad cable, connection, or fusible link.

A shorted alternator diode can cause a key-off parasitic drain; disconnect the alternator B+ and retest the drain to isolate it.

Growling or whining that tracks engine speed usually indicates alternator bearings or a loose or glazed drive belt rather than an electrical fault.

Alternators typically produce only 60-70% of rated output at idle, so output testing must be done at the specified rpm with a carbon pile or load bank.

A one-wire alternator self-excites at higher rpm, while a multi-wire unit depends on the ignition-switched and charge-lamp circuits to begin charging.

Several lamps dimming or brightening together indicates a shared ground or supply with high resistance; measure voltage drop on both the feed and ground sides.

Fast turn-signal flash with a thermal flasher means a bulb is burned out or has the wrong resistance; LED conversions require an electronic flasher or load resistors.

HID lamps use a ballast producing roughly 20,000-25,000 V at strike; do not touch the bulb glass or probe the ballast output.

Many body computers control lamps by pulse-width-modulating the ground; a DMM in duty-cycle mode or an incandescent test lamp confirms the driver output.

Headlamp switches and relays are tested under load; a resistance check alone can pass a switch that drops voltage with current flowing.

No flash on either side of the turn signals points to the flasher unit or its ground, not to the bulbs.

Cold bulb resistance is far lower than lit resistance; verify a lamp with a current-draw or load test rather than a cold ohmmeter reading.

Daytime running lamps may drive the high beam at reduced duty cycle, so a DRL fault can also affect high beam operation.

CAN bus resistance with the battery disconnected: about 60 ohms across DLC pins 6 and 14, because two 120-ohm terminating resistors sit in parallel.

A gauge pegged at full usually means an open sender circuit; a gauge stuck at empty with the sender wire grounded points to a wiring or ground fault.

Fuel gauge senders are variable resistors, commonly 0-90 ohms or 16-158 ohms depending on manufacturer; substitute a known resistor to verify the gauge.

Speedometer input comes from the VSS or from wheel speed sensors through the ABS module; an ABS module fault can affect speedometer and odometer operation.

Cluster replacement usually requires programming the VIN, odometer value, and options with a scan tool, and sometimes a theft-deterrent relearn.

The cluster bulb-check or self-test illuminates all indicators; an indicator that does not light during the test indicates a bulb, LED, or cluster fault.

Driver information messages are generated by the BCM or PCM and sent over the bus; retrieve body and communication codes before replacing the cluster.

Temperature gauges use a negative-temperature-coefficient sender: high resistance reads cold, low resistance reads hot.

Express-up/down windows must be re-initialized after a battery disconnect: run the window fully down and hold, then fully up and hold, per the service procedure.

A window that moves in only one direction usually has a faulty switch or a shorted or reversed motor circuit rather than a failed motor.

The wiper park switch keeps the motor powered until the arms reach the park position; failure leaves the blades stopping mid-windshield.

Never use an ohmmeter or powered test light on airbag circuits; disable the SRS by disconnecting the battery and waiting the specified time before service.

Key fob programming is done with a scan tool or a key-cycle and button sequence; on some systems all fobs must be reprogrammed in the same session.

Body control modules drive relays and loads; an open relay coil or a bad BCM ground can cause several unrelated accessories to fail at the same time.

Common parasitic drains are glove box, trunk, and vanity mirror lamps that stay on; verify every lamp is off before measuring current.

Power seat memory systems use potentiometers or Hall-effect sensors; working motors with a memory fault point to a position sensor or the memory module.