Diagnostic process

Code scan first. Fault confirmation before parts.

A DTC tells you which circuit, system or operating condition the ECU is unhappy with. It does not automatically tell you which part to replace. Use this test order to avoid comebacks and unnecessary parts.

Open Mobile Motive diagnostics page Known-fault bulletins Search DTCs

1. Easy checks first

Battery state of charge, terminal condition and cranking voltage under load.
Charging voltage, smart-charge command and alternator ripple where relevant.
Main fuses, relays, fusible links, water ingress, ground straps and loose connectors.
Oil level/condition, coolant level, intake duct sealing, airbox fitment and obvious vacuum leaks.

2. Confirm the complaint

Record active, pending and history codes from all modules, not just the ECU.
Save freeze-frame: coolant temp, load, RPM, road speed, voltage and fuel trims when the fault set.
Confirm whether it fails cold, hot, idle, light throttle, cruise, WOT, uphill or after refuelling.
Do not clear codes before recording data and checking readiness monitors.

3. Use live data properly

Fuel trims: idle-only lean often points to vacuum/PCV; load lean points to fuel delivery or MAF under-reporting.
MAF/MAP plausibility: compare airflow/load against engine size and boost/vacuum state.
Cam/crank: compare commanded versus actual VVT movement before replacing sensors.
ABS: compare wheel speeds while rolling slowly; one drop-out usually points to sensor/tone ring/hub/harness.

4. Prove the circuit

Back-probe with correct pins and terminal tools; do not spread terminals.
Load-test powers and grounds; a circuit can show 12 V no-load and fail under current.
Scope crank, cam, injector, ignition, CAN and wheel-speed signals for intermittent faults.
Wiggle-test harnesses while watching the scan tool or scope capture.

Professional data baselines

Test	Good direction	What a bad result normally means
Battery at rest	About 12.6 V when fully charged; load-test if uncertain.	Low SOC or weak battery can cause false module, throttle, transmission and network codes.
Cranking voltage	Generally above 9.6 V while cranking under normal conditions.	Low voltage can corrupt crank signal, immobiliser logic and module communication.
Voltage drop	Starter B+ under 0.5 V and ground under 0.3 V while cranking is a good target.	High resistance in cable, terminal, engine earth, fusible link or starter path.
Fuel trims	±5% excellent; ±10% investigate; ±20% usually a real fault.	Vacuum leak, fuel delivery, MAF bias, exhaust leak, injector issue or purge fault.
CAN resistance	About 60 Ω between CAN-H and CAN-L with battery disconnected and modules asleep.	Open termination, shorted network, failed module or wiring fault.
Relative compression	Even current humps and even cranking speed.	Mechanical fault, valve sealing, timing fault, compression loss or starter/cable issue.

Common diagnostic pathways

Symptom	First checks	Next-level testing
Check engine light	All-module scan, freeze-frame, battery voltage, visual inspection, service bulletins.	Live data, road test, circuit tests, smoke test, pressure test, scope capture.
No start / crank no start	Battery, cranking RPM on scan tool, immobiliser light, fuel level, fuses.	Crank/cam scope, injector pulse, coil trigger, fuel pressure, compression.
Misfire	Misfire counters, plug/coil/injector swap, vacuum leaks and fuel trims.	Relative compression, leakdown, injector balance, current ramp, ignition waveform.
Battery drain	Battery test, charge test, obvious lights/modules staying awake, aftermarket accessories.	Parasitic draw test, voltage drop across fuses, network sleep check, thermal camera.
ABS/traction light	Wheel-speed data, tyre size, hub play, visible harness damage.	Sensor power/signal scope, tone ring inspection, CAN/module checks.
Turbo underboost	Intake hoses, clamps, air filter, MAP/MAF data, boost command.	Smoke/pressure test, actuator duty, VNT movement, exhaust restriction and DPF data.

Technical bulletin workflow

Before replacing an expensive component, check VIN-specific OEM service information, Australian recall status and manufacturer communications. A known-fault bulletin should direct the test, not replace it. Recalls and safety campaigns are not the same as a customer-pay diagnostic repair.

Australian vehicle recall check NHTSA manufacturer communications / TSB data mobile diagnostic testing Adelaide Hills