Holden Commodore (VN-VZ), Known Issues and Common Problems
Overview
The Holden Commodore VN (1988-1991) through VZ (2004-2006) spans nearly two decades of production and encompasses three distinct engine families (Buick/Ecotec V6, Holden 304 V8, and GM LS1/LS2 V8), multiple transmission types, and two entirely different chassis platforms (VN-VS and VT-VZ). The problems differ significantly between generations.
The good news: these cars were built in enormous numbers, parts are plentiful and affordable, and the owner community has documented solutions for every known issue. The LS1/LS2 V8 in particular benefits from a global aftermarket, anything that fits a Chevrolet Corvette or Camaro will fit your Commodore.
Engine, V6 (Buick/Ecotec 3.8L, VN-VY)
Intake Manifold Gasket Leak
What happens: Coolant leak at the junction of the intake manifold and cylinder heads. May present as coolant loss without a visible external leak (coolant enters the intake ports), or as a coolant stain on the side of the engine. Engine may run rough or misfire if coolant enters the combustion chamber.
Why it happens: The intake manifold gasket on the 3.8L V6 is a composite material that deteriorates with heat cycling. Dex-Cool coolant (used by GM) has been implicated in accelerating gasket deterioration, though this is debated. The gasket sits between an aluminium intake manifold and iron cylinder heads, different thermal expansion rates stress the gasket.
How to fix it: Replace the intake manifold gasket set. The job requires removing the intake manifold, fuel rail, and associated wiring. Parts: $80-150 for a quality gasket set (Felpro is the standard recommendation). Labour: 4-6 hours. This is one of the most common jobs on the 3.8L V6, and any competent home mechanic can tackle it with basic tools and a workshop manual. Retorque the intake manifold bolts to 20 Nm in the specified sequence, over-torquing warps the manifold and guarantees a future leak.
Severity: Needs attention. Coolant loss leads to overheating. Coolant in the combustion chambers causes misfire and can wash oil off the cylinder walls.
Harmonic Balancer Failure (Ecotec, VS onwards)
What happens: A wobbling pulley on the front of the crankshaft. Knocking or rattling noise from the front of the engine. The drive belt may track poorly or come off.
Why it happens: The harmonic balancer (crank pulley) is a two-piece unit bonded with rubber. The rubber deteriorates with heat and age, allowing the outer ring to separate from the hub. The outer ring carries the serpentine belt and the crank position sensor reluctor, if it separates, the engine loses belt-driven accessories and may stall.
How to fix it: Replace the harmonic balancer. The old one must be pulled with a balancer puller, do not pry it off or you’ll damage the crankshaft nose. Torque the bolt to the specified value (200 Nm+). A new balancer is $100-250. The job takes 1-2 hours.
Severity: Urgent if the outer ring is wobbling visibly. The drive belt powers the water pump, power steering, and alternator, losing the belt disables all three.
Supercharger Bypass Valve Failure (L67 supercharged V6)
What happens: Loss of boost, rattling from the supercharger, reduced performance. The supercharger may make a whining noise that changes with the valve’s operation.
Why it happens: The bypass valve controls how much air recirculates through the supercharger at part throttle. The valve’s internal diaphragm deteriorates, causing it to stick open (no boost) or closed (excessive boost at part throttle, which loads the engine unnecessarily).
How to fix it: Replace the bypass valve actuator. Parts: $80-150 aftermarket. This is a 30-minute job. Some owners upgrade to a manual bypass valve for tuned applications.
Severity: Needs attention. A stuck-open valve means the supercharger isn’t producing boost. A stuck-closed valve can overload the supercharger and engine at part throttle.
Engine, V6 (Alloytec 3.6L, VZ)
Timing Chain and Guide Failure
What happens: Rattling noise on cold start that may persist after warm-up. Check engine light with codes related to camshaft timing. Rough idle, misfiring, loss of power. In severe cases, the engine won’t start or runs extremely poorly.
Why it happens: The Alloytec V6 uses plastic timing chain guides that become brittle with heat and age. As the guides deteriorate, the chain loses tension, stretches, and can skip teeth. The VZ Alloytec was the first application of this engine in the Commodore, and early units were more susceptible.
How to fix it: Replace the timing chains (both banks), all guides, and tensioners. This requires removing the front cover, the engine may need to come forward or partially out of the bay depending on the workshop’s preference. Parts: $300-500. Labour: 8-14 hours. Total cost at a workshop: $1,500-3,000. This is not a DIY job for most people.
Severity: Urgent. A skipped timing chain will bend valves. Do not ignore timing chain rattle on an Alloytec.
Oil Leaks from Timing Cover
What happens: Oil weeping or dripping from the front of the engine, behind the harmonic balancer area.
Why it happens: The Alloytec timing cover uses a gasket and sealant that deteriorate with age. The cover itself can warp slightly from heat cycling.
How to fix it: Reseal the timing cover. This is essentially the same job as the timing chain replacement, so do both at the same time. If you’re replacing timing chains, there’s zero additional cost to reseal the cover while it’s off.
Severity: Needs attention. Minor oil leaks aren’t urgent but should be addressed before they worsen.
Engine, V8 (Holden 304, VN-VS)
Hydraulic Lifter Noise
What happens: Ticking or tapping noise from the top of the engine, worst on cold start. May persist for several minutes or be constant.
Why it happens: The 304 V8 uses hydraulic lifters that collapse when worn. Infrequent oil changes and poor oil quality accelerate lifter wear. The lifter bores in the block can also develop wear, which allows the lifter to rock slightly and lose oil pressure.
How to fix it: Replace the lifters. On the 304, this requires removing the intake manifold, rocker covers, and rocker assemblies. Parts: $150-300 for a complete set. Labour: 6-8 hours. If the lifter bores are worn, oversized lifters or bore repair is needed.
Severity: Needs attention. A ticking lifter reduces valve opening and engine performance. Severe cases can damage camshaft lobes.
Oil Pump Drive Shaft Failure
What happens: Sudden loss of oil pressure. Oil pressure warning light illuminates. Engine noise increases rapidly. Catastrophic engine failure if not caught immediately.
Why it happens: The 304 V8’s oil pump is driven by a shaft from the distributor (or a dedicated drive on EFI models). The shaft can develop a twist or break, stopping the oil pump entirely.
How to fix it: Replace the oil pump drive shaft. This requires removing the distributor (where fitted) and extracting the shaft. Parts: $30-60. The bigger cost is the damage done before you noticed. If oil pressure drops, stop the engine immediately, do not drive the car to a workshop.
Severity: Urgent. Total oil pressure loss destroys the engine within seconds.
Rear Main Seal Leak
What happens: Oil drips from the junction of the engine and gearbox. Oil may be visible on the underside of the bellhousing.
Why it happens: The rear main seal on the 304 is a two-piece rope-type seal (early) or one-piece lip seal (later) that hardens with age. The one-piece seal is far more reliable. Many 304s have been retrofitted with the one-piece seal during rebuilds.
How to fix it: Replace the rear main seal. This requires removing the gearbox or engine. Budget $500-1,000 for the job at a workshop. If the engine is out for other reasons, the seal itself is $20-40.
Severity: Needs attention. A slow drip is tolerable. A heavy leak needs addressing before oil loss causes damage.
Engine, V8 (LS1 5.7L / LS2 6.0L, VT-VZ)
Lifter Tick
What happens: Light ticking noise from the top of the engine, usually on cold start. May or may not persist once warm.
Why it happens: The LS1 and LS2 use hydraulic roller lifters. The roller bearing in the lifter can develop a flat spot, causing a tick as it rotates on the camshaft lobe. Oil quality and change intervals directly affect lifter life. Some lifter tick is considered normal on LS engines, a light tick on cold start that disappears within 30 seconds is generally not a concern.
How to fix it: If the tick persists after warm-up, replace the affected lifter(s). On the LS1/LS2, this requires removing the intake manifold, valve covers, and rocker arms. Replacing all 16 lifters while the engine is apart is sensible. Parts: $200-400 for a complete set. Labour: 6-8 hours.
Severity: Minor if cold-start only. Needs attention if persistent after warm-up.
Valley Cover Oil Leak
What happens: Oil pools in the “valley” between the cylinder banks, visible when the intake manifold is removed. Oil may weep from the manifold area externally.
Why it happens: The LS1/LS2 has a plastic valley cover (a plate that sits between the cylinder banks, under the intake manifold) with a rubber gasket that deteriorates with heat. The knock sensors sit under this cover, and oil leaking past the gasket can damage the knock sensor wiring harness.
How to fix it: Replace the valley cover gasket. This requires removing the intake manifold. While it’s apart, inspect and replace the knock sensor wiring harness if it’s oil-soaked or brittle. Parts: $30-60 for the gasket. Labour: 2-3 hours.
Severity: Needs attention. The oil leak itself is minor, but damaged knock sensor wiring causes phantom knock codes and retarded timing, reducing performance and fuel economy.
DOD/AFM Lifter Collapse (VZ LS2 with DOD)
What happens: Misfiring on specific cylinders, rough idle, check engine light. Metallic knocking from inside the engine.
Why it happens: The VZ LS2 (some models) features Displacement on Demand (DOD), which deactivates four cylinders under light load. The DOD lifters use an internal locking mechanism that can fail, causing the lifter to collapse and the valve to not open. This is a known GM design issue affecting LS engines with DOD/AFM worldwide.
How to fix it: Replace the failed lifters. Many owners replace all lifters with non-DOD lifters and have the DOD system disabled via an ECU tune. This is the recommended long-term fix, it eliminates the problem permanently. Parts: $300-500 for non-DOD lifters. Tune to disable DOD: $200-400.
Severity: Urgent. A collapsed lifter can damage the camshaft, push rod, and rocker arm.
Transmission
4L60-E Automatic Issues
What happens: Harsh 1-2 shift, delayed engagement from Park to Drive, slipping under hard acceleration, shudder during torque converter lockup.
Why it happens: The 4L60-E is a hydraulically controlled (VN-VS) or electronically controlled (VT-VZ) 4-speed automatic. The 3-4 clutch pack and the torque converter clutch are the primary wear items. Contaminated fluid, infrequent service, and high-power applications accelerate wear.
How to fix it: Service the transmission (fluid and filter) every 40,000 km. If the transmission is already showing symptoms, a shift kit ($200-400 fitted) can extend life. A full rebuild costs $1,500-3,000. For high-power applications (modified LS1/LS2), the 4L60-E is marginal, consider a 4L80-E swap or a built 4L60-E with upgraded internals.
Severity: Needs attention. A slipping transmission deteriorates rapidly.
Manual Gearbox Synchro Wear
What happens: Grinding or crunching when shifting into 2nd or 3rd gear, especially on cold mornings or when shifting quickly.
Why it happens: Synchro rings wear with age and mileage. The T56 6-speed manual (VT II onwards) is generally robust, but 2nd-gear synchro wear is the most common complaint. Aggressive downshifting accelerates wear.
How to fix it: Synchro replacement requires the gearbox to be removed and partially disassembled. Budget $800-1,500 for a synchro rebuild. Using quality gearbox oil (Motul or Penrite) and changing it every 40,000 km helps prevent premature wear.
Severity: Needs attention. Synchro wear progresses, it won’t fix itself.
Suspension and Steering
IRS Bush Wear (VN onwards)
What happens: Clunking from the rear over bumps. Rear-end wander, particularly under braking. Uneven rear tyre wear. The car feels vague in the rear.
Why it happens: The independent rear suspension uses rubber bushings in the trailing arms, lower control arms, and differential mount that deteriorate with age. Road conditions, load, and spirited driving all accelerate wear. This is the most common suspension issue on all Commodores from the VN onwards.
How to fix it: Replace the rear bushings. A full IRS bush kit (all trailing arm bushings, diff mount bushings, and lower control arm bushings) costs $200-500 in parts. Labour: 4-8 hours. Nolathane and SuperPro both offer polyurethane bush kits that last significantly longer than rubber. Whiteline offers a complete rear bush kit that’s popular with enthusiasts.
Severity: Needs attention. Worn rear bushings compromise handling stability, especially under braking and in emergency manoeuvres.
Power Steering Rack Leak (VT-VZ)
What happens: Power steering fluid on the garage floor, heavy steering at parking speeds, whining from the power steering pump.
Why it happens: The power steering rack seals wear with age. The VT-VZ rack is a well-made unit, but seals deteriorate after 15+ years. Low fluid from the leak accelerates pump wear.
How to fix it: Replace or recondition the steering rack. A reconditioned rack is $300-500 exchange. New racks are $500-800. Labour: 3-5 hours.
Severity: Needs attention. A sudden loss of power steering assist is dangerous, particularly at low speeds.
Front Strut Top Mount Failure (VT-VZ)
What happens: Clunking noise when turning the steering wheel, particularly at low speeds and full lock. A “crunching” sensation felt through the steering wheel.
Why it happens: The rubber bearing in the front strut top mount deteriorates. The metal bearing inside can also corrode and bind.
How to fix it: Replace the front strut top mounts. Parts: $80-150 per side. Replace the struts at the same time if they’re leaking or have high mileage. Total front suspension refresh (struts, top mounts, control arm bushings, tie rod ends): $800-1,500.
Severity: Needs attention. Not dangerous in itself, but indicates the front suspension is overdue for a refresh.
Electrical
Body Control Module (BCM) Issues (VT-VZ)
What happens: Intermittent electrical faults, interior lights stay on, power windows stop working, central locking misbehaves, dashboard warning lights illuminate randomly, the car may not crank.
Why it happens: The BCM is the central control module for the body electrics. It communicates with the engine control module (ECM), instrument cluster, and various sub-systems via CAN-bus wiring. The BCM can develop internal faults from age, moisture ingress, or power surges. The connector pins can also corrode.
How to fix it: Diagnosis first, a Tech2 or compatible scan tool can read BCM fault codes. Connector cleaning sometimes resolves intermittent issues. A faulty BCM must be replaced and programmed to the car’s VIN and immobiliser system. A secondhand BCM needs programming: $100-200 at an auto electrician. A new BCM from the dealer (where available) is $300-600.
Severity: Needs attention. A faulty BCM can cause multiple seemingly unrelated electrical issues that are maddening to diagnose individually.
Alternator Failure
What happens: Battery warning light on the dash, dim headlights, accessories losing power, battery going flat.
Why it happens: The alternator wears with age. The VT-VZ alternator operates at high output to support the car’s electrical demands. Internal rectifier and regulator failure are the most common modes.
How to fix it: Replace the alternator. Test output first: 13.8-14.4V at idle with accessories off. VN-VS alternators are straightforward to replace. VT-VZ alternators are slightly more difficult due to packaging but still a 1-2 hour job. Parts: $200-400.
Severity: Needs attention. A failing alternator will eventually strand you.
Body
VN-VP Boot Floor and Sill Rust
What happens: Rust perforations in the boot floor, sills, and rear wheel arches. Water in the boot, bubbling paint along the sills.
Why it happens: Same as every Australian car of the era, water ingress through taillight seals, stone chip damage, and trapped moisture in enclosed sections.
How to fix it: Cut out and weld in repair panels. Treat surface rust early with rust converter and sealer. Professional sill repair: $1,500-4,000 per side.
Severity: Urgent if structural (sills). Needs attention for cosmetic areas (boot floor, wheel arches).
Paint Peel (VT-VX, specific colours)
What happens: Clear coat peels from the roof, bonnet, and boot lid. Paint appears chalky and dull before peeling.
Why it happens: Certain VT-VX paint colours (particularly some metallics) suffered from clear coat adhesion problems. UV exposure and poor factory prep contribute. The VT-VX is more affected than the VY-VZ.
How to fix it: The only proper fix is a respray of the affected panels. Budget $1,500-3,000 for a quality respray of the roof, bonnet, and boot. Alternatively, a cut-and-polish can delay peeling if the clear coat is just beginning to cloud.
Severity: Minor functionally, but it looks terrible and affects resale value.
Preventive Maintenance
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Change engine oil every 7,500-10,000 km. Use 5W-30 semi-synthetic for V6, 5W-30 full synthetic for LS1/LS2. Quality oil prevents lifter wear on all engine types.
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Service the automatic transmission every 40,000 km. Fresh fluid and a filter keep the 4L60-E alive. Don’t flush, drain and fill. Flushing can dislodge debris that blocks passages.
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Replace IRS bushings proactively at 150,000 km. Don’t wait for them to clunk, worn bushings compromise handling long before they make noise.
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Inspect the intake manifold gasket (V6) at every service. Look for coolant stains around the manifold. Early detection prevents overheating.
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Address VZ Alloytec timing chain rattle immediately. This is not a “wait and see” problem. Rattling chains skip teeth and destroy engines.
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Clean the throttle body every 40,000 km. Carbon buildup in the throttle body causes rough idle and stalling on all models.
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Check power steering fluid level monthly. A slow rack leak can go unnoticed until the pump is damaged from running dry.
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