Holden Commodore Diagnostic Guide

Fix it yourself.
Know exactly why.

The VX/VY Commodore diagnostic checklist — systematic fault code guides, sensor tests, and repair workflows built for owners who want to understand their car.

VX · VY · VZ Compatible
OBD2 & ALDL Coverage
40+ Diagnostic Procedures
P-codes & B-codes Included
Scroll to explore
Common fault codes on VX/VY Commodores
P0300 misfire
P0301 cyl 1
P0171 lean
P0172 rich
P0420 cat eff
P0443 purge
P0455 evap leak
P0507 idle spd
C1235 ABS
B1000 ECU
P0335 crank pos
P0341 cam pos
P0120 TPS
P0115 ECT

What the guide covers

Fault codes are the starting point — not the answer. Every code has a diagnostic tree.

01

Engine Management

18 checks
Misfire diagnosis — P0300 to P0306
Fuel trim analysis — LTFT/STFT deep dive
O2 sensor waveform interpretation
Crankshaft & camshaft position sensors
MAF & MAP diagnostics for the Ecotec V6
02

Emissions & EVAP

9 checks
EVAP system smoke test procedure
P0443 purge solenoid diagnosis
Catalytic converter efficiency — real vs false
Gas cap pressure test & leak detection
P0455 gross leak vs small leak differentiation
03

Chassis Systems

11 checks
ABS sensor — tone ring vs wiring diagnosis
Brake pad compensation motor fault C1235
Wheel speed sensor resistance tables
Suspension height sensors — VP-VZ
Steering angle sensor calibration
04

Body & Network

7 checks
B1000 ECU internal fault — conditions & resolution
Holden CAN bus fault code interpretation
HVAC actuators — blend door motor tests
Instrument cluster — dead gauges
Remote key fob & BCM pairing procedures
Inside the guide
P0300 Misfire
P0171 Lean
C1235 ABS
Fault Code Reference
Code Definition Common Cause Severity
P0300 Random/Multiple Cylinder Misfire Vacuum leak, bad coil, plug gap, cam sensor High
P0301–P0306 Cylinder-specific misfire (1–6) That cylinder's coil, plug, or injector High
Diagnostic Procedure
1
Check freeze frame data
What was RPM, load, and coolant temp when the code set? A misfire at idle points to plugs/coils; under load, more likely fuel or compression.
2
Switch coil packs between cylinders
Move the suspected bad coil to a good cylinder. If the misfire moves with the coil, replace it. If it stays, the problem is plug or injector.
TorqueLab note: Ecotec V6 coil packs fail most commonly on cylinders 2 and 5 — check those first.
3
Measure plug gap with a wire gauge
Spec is 1.0–1.1mm for the Holden 3.8L Ecotec. Gapped wide = misfire under load. Gap too narrow = fouling under idle.
4
Vacuum leak check — smoke machine or Propane enrichment
Spray carb cleaner around intake manifold joints while monitoring RPM. A vacuum leak will lean the mixture and often clear a P0300.

Built for owners,
not workshops.

Mechanics learn from experience and expensive scan tools. TorqueLab translates that knowledge into a systematic process any Holden owner can follow — with a $30 generic OBD2 scanner and a multimeter.

Every guide in the checklist was built from Holden service data, real-world forum cases from Aus-car forums, and diagnostic records from VY/VZ owners. If it's in the guide, it's because someone actually needed it.

No "try this first." No vague advice. Just step-by-step logic trees backed by actual specifications.

45
Fault codes covered
40+
Diagnostic procedures
VX–VZ
Model range
The Mission

Every Holden owner
deserves to know what's wrong.

The forum posts are scattered. The YouTube videos are shallow. The mechanic charges $180/hr to tell you to "try the coil packs." TorqueLab changes that — systematic, accurate, built for owners who care enough to learn.

OBD2 Compatible ALDL Compatible No Subscriptions VX/VY/VZ
TorqueLab

Australian made. Sydney, NSW.