DIAGNOSTIC WORKFLOWS.

Record whether there is silence, a click, repeated clicking or partial rotation. Confirm gear position and immobilizer messages.

Test at the posts—not the cable ends. If voltage collapses, evaluate battery condition, connections and possible excessive starter or mechanical load.

Use scan data to check ignition/start request, brake or clutch input, transmission range, theft status and starter command.

If the starter is commanded, verify relay control, terminal 50 voltage and ground-side control according to the diagram.

Measure positive- and ground-side voltage drop during the crank request. Do not judge the cables with an unloaded resistance test.

Compare current with voltage and engine movement. High current with no rotation differs from low current caused by resistance or poor motor contact.

Repeat cranking voltage, current and voltage-drop measurements; rescan all involved modules.

Confirm even cranking cadence, acceptable speed and stable module voltage. An uneven cadence can justify relative compression before parts are removed.

Save codes from all modules and review theft, start authorization, engine speed and synchronization status while cranking.

Confirm RPM is reported and cam/crank synchronization is achieved where supported. Scope CKP and CMP together if the relationship is questionable.

Check injector command, ignition command, appropriate fuel-pressure data and airflow plausibility. Avoid uncontrolled spark or fuel tests.

If commands and fuel are present, use relative compression, absolute compression, leak-down or timing verification as indicated.

Consider fuel contamination, flooded operation, restricted exhaust and incorrect valve timing only after the initial evidence supports them.

Verify start time, sync, pressure and codes under the original failure condition.

Save codes, freeze-frame and misfire counters with RPM, load, temperature, trims and loop status.

A single cylinder directs testing toward its ignition, injector and mechanical condition. Multiple cylinders require bank and shared-system comparisons.

Compare ignition waveforms, injector current, exhaust or intake pulsation and relative compression before moving components.

Compare trims by bank and at idle versus load. Look for air leakage, supply limits, purge flow, fuel quality or an exhaust leak.

Use appropriate coil, plug, injector flow/current, compression, leak-down or in-cylinder testing. A misfire counter does not identify the failed part.

Limit operation during an active severe misfire and follow manufacturer precautions for cylinder-disable tests.

Repeat the drive condition and confirm counters, trims and waveform comparisons.

Determine whether the engine cannot produce torque, the controller is limiting torque or the transmission/driveline is not transferring it.

Record module codes, freeze-frame, torque-reduction status and any protection mode before cycling the ignition or clearing memory.

Compare pedal, desired and actual throttle, desired and actual boost, airflow, calculated load, fuel pressure and commanded torque.

Test for intake restriction, charge-air leakage, boost-control response and exhaust restriction based on the captured pattern.

Compare desired and actual low- and high-side pressure with pump or regulator command. Do not open a high-pressure system without the OEM procedure.

Evaluate cam timing response, ignition retard, misfire activity and mechanical breathing if airflow remains low.

Confirm torque, airflow, pressure and boost now follow their requests without returning codes.

Inspect, measure open-circuit state and perform the appropriate battery test. A deeply discharged or defective battery changes system behavior.

Save charging, battery-monitor, communication and undervoltage codes. Review battery state-of-charge and current-sensor plausibility where supported.

Modern systems vary target voltage. Compare scan request, alternator feedback and DMM measurement at the battery.

Use a current clamp to compare alternator output with vehicle demand and battery charge current under controlled loading.

Measure positive and ground voltage drop from alternator to battery while output is elevated.

Evaluate alternator ripple and any LIN or other control circuit only after power, ground, belt and connection integrity are established.

Follow OEM procedures after battery or monitored-component replacement, then verify multiple operating modes.

Do not diagnose key-off current with a damaged or incompletely charged battery.

Latch closures as required, secure keys, configure the meter or clamp and note the manufacturer’s normal sleep process.

Watch current from key-off through sleep. Note timed steps, modules that remain active and the stabilized value.

Use logging, min/max or a scope/current clamp when the drain is not continuously present.

Use wiring and fuse-distribution information. Voltage across fuses can help screen active branches without pulling fuses and waking modules.

Check command, wake network, stuck relay, module input, aftermarket accessory or internal module behavior before replacement.

Verify normal shutdown and at least one representative wake/sleep cycle after repair.

Confirm the specified type and rating. Record whether it opens immediately, after vibration, during movement or only when a load is commanded.

Use the diagram to list loads, splices, connectors and harness sections supplied by the circuit.

Use an approved resettable breaker, current-limited supply or suitable test load for the circuit. Do not bypass protection with an unrestricted jumper.

Separate a load drawing excessive current from a power wire contacting ground.

Disconnect downstream branches methodically while monitoring current. Avoid random harness disassembly.

Inspect movement points, heat exposure, bracket contact, water intrusion and prior repairs. Use controlled wiggle or thermal testing.

Install the correct fuse, operate every protected load and confirm current remains within the circuit design.

List responding and non-responding modules and every U-code reporter before cycling power or clearing codes.

Use topology and wiring information to determine whether missing modules share a gateway, network branch, wake line, power feed or ground.

Load-test all constant, ignition and ground circuits. Check wake or enable inputs before blaming the physical network.

Apply CAN, LIN, Ethernet or other protocol-specific checks. Do not use CAN resistance expectations on a different network.

If multiple networks are involved, confirm gateway power, configuration, communication and routing.

Disconnect branches using OEM guidance and monitor restoration. Safety and security modules may require special procedures.

Confirm every expected module reports, communication codes do not return and the repair did not create a key-off wake issue.

Measure battery condition and voltage during wake-up. Low auxiliary voltage can prevent modules, contactors and interlocks from initializing.

Save codes, status and freeze data from the battery, inverter, charger, gateway, brake, restraint and body systems.

Review key authorization, brake input, gear state, charge-cable status, crash status, isolation status and thermal limits.

Use scan data for precharge request, bus voltage, pack voltage, contactor command and feedback. Do not infer contactor state from sound alone.

Follow OEM pinpoint tests. A high-voltage interlock or isolation fault requires qualified procedures and specified equipment.

Verify power, ground, wake and communication at the module preventing Ready authorization before considering an HV component fault.

Follow the manufacturer sequence, confirm Ready mode, propulsion, charging and absence of returning safety faults.