Porsche 911 Carrera S 991

The 991 uses 7-10 electric changeover valves (COVs) to control exhaust flaps, heater shut-off valves, coolant routing, the acoustic simulator, and fuel tank ventilation. These solenoid-operated valves are prone to moisture ingress, which causes internal corrosion and eventual electrical failure. Porsche addressed early 2012 builds with a service campaign (WC-43) replacing eight valves, but later cars can still develop the issue. Symptoms range from loss of cabin heating and check engine lights to exhaust flap malfunction. Individual valves cost around €30-60, but multiple failures and labor add up. A typical repair involves replacing 2-4 failed valves at once, costing €400-800 at a specialist. When multiple COVs fail together (common, since they are all the same age), costs can reach €1,000-1,500 including diagnosis.

PADM (Porsche Active Drivetrain Mount) engine mounts are standard on the Carrera S and use electronic sensors to adjust mount stiffness. The internal sensors, which are glued inside the mount, fail regularly due to heat exposure and vibration. A PADM fault warning appears on the dashboard, and the car reverts to a firmer, uncontrolled mount behavior. Porsche dealers typically quote €1,200-2,500 per mount for full replacement. However, in most cases the mount itself is structurally fine and only the sensor has failed. Aftermarket replacement sensors from specialists like Zuffenparts cost around €200-220 and can be fitted by a specialist in under an hour, bringing total repair cost to €300-500. Full OEM mount replacement is only necessary if the rubber or hydraulic fluid inside has actually deteriorated, which is less common.

The water pump on 991.2 models (particularly 2017-2018 production) has a known failure point where the plastic coolant pipe meets the pump housing. Porsche extended the warranty on the water pump to 10 years in North America, though European coverage has varied by market. The failure typically starts as a slow coolant leak that can progress to complete pump failure. On 991.1 models, the thermostat housing can also develop leaks, though this is less common. A replacement water pump costs approximately €300-500 for the part, with 3-4 hours of labor. Total repair runs €1,200-1,800 at a Porsche dealer or €800-1,200 at an independent specialist. Always check coolant level and look for residue around the pump housing during inspection.

The 7-speed PDK is generally reliable when properly maintained, but when failures occur, they are expensive. The most common issue is the distance sensor, triggering fault codes P1731-P1734, which results in limp mode or loss of reverse. Some 991s also develop 7th gear engagement issues related to shift fork wear. Porsche dealers typically recommend full transmission replacement at €15,000-20,000, but specialist PDK repair shops can fix most sensor and solenoid issues for €3,000-8,000. The key to prevention is regular PDK fluid changes. Porsche specifies every 120,000 km or 12 years, but specialists recommend every 60,000 km or 6 years. Cars used primarily for short trips or track days without fluid service are at highest risk. Manual transmission cars avoid this issue entirely.

Cars equipped with PASM (standard on S models) use electronically controlled dampers that adjust firmness. Over time, the internal hydraulic seals deteriorate from heat and moisture, leading to oil misting or leaks visible on the damper body. Symptoms include harsher ride quality, PASM warning lights, and inconsistent damping response. Individual OEM replacement dampers cost approximately €400-600 each. With labor and alignment, replacing a pair runs €1,500-2,000, while all four can reach €3,000-3,500. This is primarily an age-related wear issue that typically appears after 80,000-120,000 km. Upper shock mounts can also dry out and produce a low-frequency thump over rough surfaces.

The automatic rear spoiler is designed to raise at highway speeds and retract when slowing. The wiring harness that supplies power to the high-level brake light runs through the spoiler mechanism and flexes each time the spoiler cycles. This constant movement combined with heat from the engine causes wires to dry and break, resulting in an intermittent brake light warning. A separate issue involves the spoiler motor or spring mechanism failing entirely. Wiring harness replacement runs €500-800, while a full spoiler motor replacement at a Porsche dealer can cost €2,000-2,500. Specialist repair of the motor mechanism is often possible for €800-1,200.

The 991's front-mounted radiators and AC condenser sit low and exposed behind the front bumper, making them susceptible to stone chips and road debris. Over time, this causes coolant or refrigerant leaks. Damaged units cannot be repaired. A radiator replacement costs approximately €800-1,200 per side at a specialist, while an AC condenser replacement runs €600-1,000. In severe cases where both components are damaged, total costs reach €2,000-2,500 including labor.

This issue affects 991.2 Carrera S models only (3.0L twin-turbo). The original oil feed lines to the turbochargers lacked a one-way valve, allowing oil to pool inside the turbo housing after engine shutdown. On cold start, this excess oil burns off, producing visible smoke from the exhaust. Over time, this can lead to turbo seal failure. According to some specialists, 20-25% of 991.2 cars sold developed turbo-related issues within 12 months. Porsche acknowledged the issue with Technical Service Bulletin SY211655, and redesigned oil feed lines with an integrated check valve are now available. Cars built after May 2017 typically have the revised lines from factory. The cost of replacing oil feed lines alone is €500-800, but if turbo damage has occurred, replacement runs €2,000-5,000 per turbo including labor.