Subaru Impreza: common faults & what to check

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Turbo Impreza variants (GD/GG and GH/GR WRX and STI, heavily represented among NZ JDM imports) crack piston ringlands, especially the EJ255 and any car that has been tuned, run lean, or fed 91 octane. A cracked ringland shows up as compression loss and oil consumption in one cylinder and means an engine rebuild. NZ has a huge population of ex-Japan WRXs with unknown tuning history, which makes a compression/leak-down test essentially mandatory on any turbo Impreza.

Where to look: Engine internals — pistons; verified only by compression/leak-down test through the spark plug holes

Parts involved: Turbocharger.

Can't confirm for this car

Unconfirmed. This entry does not match our record of which engines and years this model was sold with, and is awaiting review. Confirm it against the car before acting on it.

Non-turbo 2.5 Imprezas (GD 2.5i/RS and GH/GE 2.5i) share the EJ251/EJ253 external head gasket leak that plagues same-era Foresters and Legacys — a slow oil/coolant weep at the head-to-block joint from around 150,000 km that eventually causes coolant loss and overheating. JDM 1.5/2.0 EJ15/EJ20 cars (the bulk of NZ imports) are much less affected, so this mainly matters on NZ-new and US-spec 2.5 cars. Repair is both sides with MLS gaskets plus timing belt/water pump while apart.

Example of the part — not this vehicle

Where to look: Head-to-block joint, both sides of the boxer engine, low in the bay

Parts involved: Head gasket.

Can't confirm for this car

The GJ/GP Impreza FB20 2.0 engine consumes oil from piston ring wear on high-mileage examples. Oil consumption above 1 litre per 5000km is abnormal.

Where to look: FB20 engine cylinder bores, piston rings, and valve stem seals

Can't confirm for this car

GD-generation Impreza WRX STI models fitted with the Driver's Control Centre Differential (DCCD) use an electro-hydraulic actuator to vary the torque split ratio of the centre differential between 35:65 and 50:50 front-to-rear on demand. The actuator solenoid and position sensor assembly is susceptible to moisture ingress from the tunnel area and develops internal corrosion that either causes the actuator to stick at a fixed position or fail open, locking the DCCD into a set torque split regardless of driver input or the automatic mode logic. A stuck-closed actuator causes heavy understeer and binding during tight-radius turning, with associated driveline clunking.

Where to look: DCCD actuator unit on the centre differential assembly inside the transmission tunnel

Parts involved: Differential.

Can't confirm for this car

The EJ154 1.5-litre engine introduced on the GH-generation Impreza (base model, not WRX) uses a timing chain that has documented premature stretch and chain guide wear, particularly after 80,000–120,000 km. Unlike the larger EJ20, the EJ154 has less robust guide material. Chain stretch causes timing retard, rough idle, and increased fuel consumption. In severe cases the chain can skip a tooth or break, causing valve-to-piston contact. This was a new failure mode not seen on the earlier EJ15.

Example of the part — not this vehicle

Where to look: Front of engine, behind the timing cover on the driver's side

Parts involved: Timing chain.

Can't confirm for this car

GK/GT Imprezas were caught in the huge Denso fuel pump recall: the pump impeller can swell, causing hesitation, rough running, or the engine stalling without restart — potentially at speed. Subaru recalled affected 2017-2019 Imprezas in NZ and Australia and replaces the pump free. The check is whether this specific car actually had the recall done; imports and cars with lapsed ownership records sometimes slipped through.

Where to look: In-tank fuel pump, under the rear seat/fuel tank

Parts involved: Water pump.

Can't confirm for this car

The FB20D engine fitted to the GK/GT Impreza uses rubber valve stem seals that harden and lose elasticity as mileage accumulates, typically becoming problematic after 80,000-120,000 km. Degraded seals allow engine oil to drain past the intake and exhaust valve guides during overnight cold soaks, pooling in the combustion chamber and producing a puff of blue-grey smoke on initial cold startup. Oil consumption accelerates as the condition progresses, and the smoke disappears after the first minute of running, which can allow the issue to be missed during a brief inspection.

Where to look: Cylinder head valve guides, exhaust tailpipe

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The e-Boxer mild hybrid system fitted to select Impreza models uses a lithium-ion traction battery (approximately 118 V) housed beneath the rear seat/boot floor to power an electric motor integrated between the engine and CVT. As with all lithium-ion chemistry, the battery undergoes capacity degradation over time and charge cycles, reducing the electric assist contribution and fuel economy. In more advanced degradation, the battery management system may disable the hybrid assist entirely and store fault codes, and partial cell failure can trigger hybrid system warning lights that require dealer diagnosis with Subaru Select Monitor.

Where to look: High-voltage lithium-ion battery pack beneath rear seat and boot floor

Can't confirm for this car

The EyeSight dual-camera system mounted behind the upper windshield on GK/GT Impreza is susceptible to internal condensation and fogging between the camera housing and windshield glass, triggered by temperature cycling, age of the windshield interlayer, or minor stone chip contamination near the camera bracket zone. Once fogged, the EyeSight system disables itself as it cannot achieve stereo image lock. Critically, any windshield replacement on an EyeSight-equipped model mandates an OEM-spec glass and a dealer-performed stereo camera recalibration, making even a minor chip repair economically significant.

Where to look: Upper centre windshield behind rear-view mirror, EyeSight camera bracket

Can't confirm for this car

The GE-series Impreza replaced hydraulic power steering with a column-mounted electric power steering (EPS) unit, and the steering rack itself uses a rack-and-pinion design with a spring-loaded yoke that holds the rack against the pinion gear. Over time the yoke adjuster preload diminishes due to wear of the plastic yoke pad, allowing the rack to develop measurable radial play. This produces a knock or rattle over road imperfections that is transmitted directly through the steering column to the wheel. Additionally, the EPS control module can develop software or sensor faults that cause intermittent loss of power assist or a steering wheel that requires excess effort on one lock, logged as fault code C0057 or C1511.

Where to look: Steering rack mounted transversely across the front subframe; EPS motor and control unit on the steering column under the dashboard

Parts involved: Steering rack.

Can't confirm for this car

The GK/GT's Harman-built infotainment unit is known for freezing, rebooting mid-drive, losing Bluetooth pairing, and blanking the reversing camera. A US class action (Udeen v. Subaru) covered 2017-2018 models and Subaru issued multiple firmware updates; units that still misbehave after updates need replacement, and out of warranty that is an expensive part even second-hand. A dead reversing camera display is a safety annoyance and can be a haggling point.

Where to look: Dashboard head unit / centre screen

Can't confirm for this car

The brake vacuum servo (booster) fitted across all three Impreza generations uses a rubber diaphragm to multiply pedal force using manifold vacuum. On EJ15 and EJ20 engines the manifold vacuum can be lower than specification due to age-related inlet manifold gasket leaks and idle control valve degradation, which reduces servo effectiveness. On higher-mileage examples the servo diaphragm itself cracks or stiffens, causing a total or partial loss of brake assistance. This results in a dramatically increased pedal effort required to achieve the same braking force, which can be dangerous in emergency situations. A failed servo can also allow a vacuum hiss from the servo housing.

Where to look: Brake vacuum booster unit mounted on the firewall directly behind the brake master cylinder

Parts involved: Intake manifold.

Can't confirm for this car

The front lower control arm ball joints on both GD and GE Impreza models are a serviceable pressed-fit design, but the ball joint housing is vulnerable to accelerated wear when driven over the unsealed roads common in New Zealand. Grit and water ingress past the rubber boot causes the steel ball and socket to wear unevenly, increasing radial and axial play beyond the manufacturer's specification of approximately 0.5 mm. Once wear exceeds this limit the wheel can track inconsistently under braking and cornering, and in severe cases the joint can separate without warning, causing total loss of steering and wheel control. Both the GD MacPherson strut and GE multi-link front geometry rely on the lower ball joint as the primary lateral locating point.

Example of the part — not this vehicle

Where to look: Front lower control arm, outboard end adjacent to the steering knuckle, both left and right sides

Parts involved: Ball joint.

Can't confirm for this car

The GK/GT Impreza (2016 onward) global platform uses front lower control arms with pressed rubber bushes that have shown premature degradation in Australasian conditions. Bush failure causes increased toe variation under braking and cornering, which produces understeer, steering wander, and increased tyre wear. This is documented across the GK global platform including XV and Forester variants on the same architecture. Bush collapse is accelerated on cars driven on unsealed or corrugated roads.

Example of the part — not this vehicle

Where to look: Front lower control arm pivot bushes at subframe mounting points, both sides

Parts involved: Ball joint.

Can't confirm for this car

The GD Impreza front strut hub carriers (knuckles) are cast iron and in New Zealand's coastal and high-rainfall regions develop severe surface corrosion that penetrates into the wheel bearing bore and brake caliper mounting faces. Severe rust swells the bore, causing the wheel bearing outer race to spin in the housing (spun bearing), which cannot be corrected by a bearing replacement alone — the knuckle itself must be replaced. The brake caliper slide bolt threads also corrode into the knuckle bosses, requiring heat and extraction, and seized ABS reluctor ring mounting faces complicate brake disc replacement.

Where to look: Front strut hub carriers (steering knuckles) on both sides, behind the front wheels

Parts involved: Shock absorber / strut.

Can't confirm for this car

GP/GJ Impreza front wheel bearings have a documented pattern of premature failure, typically appearing in the 80,000–140,000 km range. The front bearing design on this platform is not as robust as earlier generations. AWD torque loads through the front hubs under hard cornering and acceleration accelerate wear. Failure often presents as a directional hum that changes character when cornering. Left too long, a failed front bearing affects steering, braking stability, and ABS sensor function.

Where to look: Front hub assemblies behind brake disc, left and right front corners

Parts involved: Wheel bearing.

Can't confirm for this car

GD/GG and GH/GR Impreza rear wheel bearings have a documented shorter-than-expected service life, particularly on all-wheel-drive variants where the rear axle carries more load and is subject to greater lateral stress in corners. Bearings commonly fail in the 100,000–160,000 km range. NZ/AU roads and gravel exposure accelerate wear. Failure can progress from a hum to a roar, and in advanced cases can allow wheel play which affects brake and suspension geometry.

Where to look: Rear hub assemblies (left and right), inside the wheel hub behind the brake disc

Parts involved: Wheel bearing.

Can't confirm for this car

Front CV joint boots crack with age allowing grease to escape and contamination to enter. Worn joints click when turning at low speed under power.

Example of the part — not this vehicle

Where to look: Front driveshaft CV joints and boots

Parts involved: CV joint and boot.

Can't confirm for this car

Front and rear brake caliper guide pins seize from corrosion causing uneven pad wear.

Where to look: Front and rear brake calipers

Parts involved: Brake disc and pads.

Can't confirm for this car

The GE/GH Impreza generation introduced electric power steering (EPS) in place of the hydraulic system used on the GD. The intermediate steering shaft coupling between the EPS motor column and the steering rack pinion develops a creak, knock, or clunk, particularly at low speed and when the steering is loaded during parking manoeuvres or at walking pace. Subaru issued a TSB addressing the issue through lubrication of the intermediate shaft splines and universal joint with a specified molybdenum disulphide grease. In some cases the EPS motor itself develops a groan under maximum steering lock.

Where to look: Intermediate steering shaft universal joint coupling, located on the firewall between the EPS column and the steering rack

Parts involved: Steering rack.

Can't confirm for this car

The TR580 Lineartronic CVT on GK/GT Impreza models has documented fluid seepage from the external cooler lines (rubber-to-metal crimp joints) and the CVT filter housing o-ring on higher-mileage or aged units. CVT fluid is a thin, reddish oil and the seeps are often subtle but visible as pink-red staining on the underside of the transmission tunnel and subframe. Loss of CVT fluid is serious as the TR580 is highly sensitive to fluid level; even slight underfilling accelerates belt and pulley wear and can lead to catastrophic unit failure.

Where to look: CVT transmission underside, cooler line crimp joints, filter housing on transmission casing

Can't confirm for this car

GH/GR Impreza AWD models commonly develop oil leaks at the rear differential output shaft seals. The seals deteriorate with age and heat cycling, allowing differential oil to weep onto the driveshafts and rear subframe. Left unattended, oil loss from the rear diff leads to differential wear and eventual bearing failure. This is a documented pattern on AWD Subaru platforms of this era and is often found during pre-purchase inspections.

Where to look: Rear differential housing, left and right output shaft seal points where driveshafts exit

Parts involved: Differential.

Can't confirm for this car

The rear differential fitted to GD AWD Imprezas develops oil leaks from the pinion input shaft seal and both rear axle side seals. The pinion seal is a lip-type rubber seal that hardens with heat cycling and begins to weep gear oil past the propeller shaft flange. Side seals deteriorate similarly, allowing gear oil to migrate down the inside of the rear axle shafts and contaminate the rear brake drums or disc assemblies. Neglected leaks cause the rear differential to run low on oil, leading to hypoid gear and bearing damage. NZ conditions with gravel road dust and moisture accelerate lip seal deterioration.

Where to look: Rear differential housing — pinion seal at the front face, side seals at each rear axle exit point

Parts involved: Differential.