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2020 Audi S4 Problems: 4 Known Issues

2020 model year · 107+ owner reports · Updated September 2026

According to Au7o's analysis of 107+ owner reports, the 2020 Audi S4 has 4 documented known issues, with 3 rated critical. The most serious are Seat-Heater Cable Contact Fault Disables the Passenger Airbag (Recall 21V874 / 74E3) ($0-$0 repair), EA839 3.0T Water Pump Internal Seal Failure Leaks Coolant Into the Vacuum System (Class Action) ($1,200-$3,000 repair) and Rear Axle Trailing Arm Eccentric Bolt Lock Nut Can Break from Stress Corrosion (Recall 21V295 / 42L1) ($0-$0 repair). The most commonly reported issue is Thermostat Housing Failure and Coolant Leak with 107 owner reports. Across all issues with published estimates, repair costs range from $300 to $3,000. DIY maintenance guides at au7o.io.

Frequently Asked Questions

What are the most common Audi S4 problems?

According to Au7o's analysis of 107+ owner reports, the 2020 Audi S4 has 4 documented issues. The most frequently reported are: Seat-Heater Cable Contact Fault Disables the Passenger Airbag (Recall 21V874 / 74E3), EA839 3.0T Water Pump Internal Seal Failure Leaks Coolant Into the Vacuum System (Class Action), Rear Axle Trailing Arm Eccentric Bolt Lock Nut Can Break from Stress Corrosion (Recall 21V295 / 42L1). Of these, 3 are rated critical and should be addressed promptly.

Is the Audi S4 reliable?

The 2020 Audi S4 has 4 known issues documented across 107+ owner reports. 3 issues are rated critical: Seat-Heater Cable Contact Fault Disables the Passenger Airbag (Recall 21V874 / 74E3) and EA839 3.0T Water Pump Internal Seal Failure Leaks Coolant Into the Vacuum System (Class Action) and Rear Axle Trailing Arm Eccentric Bolt Lock Nut Can Break from Stress Corrosion (Recall 21V295 / 42L1). Prospective buyers should inspect for these issues and factor potential repair costs into their purchase decision. Regular maintenance following the manufacturer's schedule helps prevent many common problems.

How much does it cost to fix common Audi S4 problems?

Repair costs for known Audi S4 issues range from $0 to $3,000, depending on the specific problem and whether you choose DIY or professional repair. The most critical issue, Seat-Heater Cable Contact Fault Disables the Passenger Airbag (Recall 21V874 / 74E3), typically costs $0-$0 to repair. Au7o provides step-by-step DIY maintenance guides that can help reduce repair costs.

What is the 2018-2020 Audi S4 Seat-Heater Cable Contact Fault Disables the Passenger Airbag (Recall 21V874 / 74E3)?

On B9 S4 sedans, the cable connecting the front passenger seat heater to the Passenger Occupant Detection System (PODS) can develop a contact fault. The PODS software reads the fault as a system malfunction and switches the passenger front airbag OFF, so the airbag will not deplo… Repairs typically run $0-$0. Severity: high.

What is the 2018-2025 Audi S4 EA839 3.0T Water Pump Internal Seal Failure Leaks Coolant Into the Vacuum System (Class Action)?

The B9 S4's turbocharged EA839 3.0T uses a water pump whose internal seals fail, and the failure mode is unusual: coolant does not only weep externally, it is drawn INTO the engine's vacuum circuit and other places coolant should never reach, contaminating vacuum lines and compon… Repairs typically run $1,200-$3,000. Severity: high.

What is the 2020-2021 Audi S4 Rear Axle Trailing Arm Eccentric Bolt Lock Nut Can Break from Stress Corrosion (Recall 21V295 / 42L1)?

Lock nuts from particular production batches used on the eccentric bolt at the rear-axle trailing arm can crack from stress corrosion. If the nut breaks, the eccentric bolt can move and the rear-axle wheel alignment changes - and at higher speed the rear axle can suddenly and unc… Repairs typically run $0-$0. Severity: high.

What is the 2010-2025 Audi S4 Thermostat Housing Failure and Coolant Leak?

The plastic thermostat housing on the S4 3.0T is prone to cracking and leaking coolant. The housing sits at the rear of the engine making leaks hard to spot until coolant loss is significant. Repairs typically run $300-$800. Severity: medium.

2020 Audi S4 Problems: 4 Known Issues

All 4 Known Issues

2018-2025 Audi S4: EA839 3.0T Water Pump Internal Seal Failure Leaks Coolant Into the Vacuum System (Class Action)#

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2010-2025 Audi S4: Thermostat Housing Failure and Coolant Leak#

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2018-2020 Audi S4: Seat-Heater Cable Contact Fault Disables the Passenger Airbag (Recall 21V874 / 74E3)#

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2020-2021 Audi S4: Rear Axle Trailing Arm Eccentric Bolt Lock Nut Can Break from Stress Corrosion (Recall 21V295 / 42L1)#

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Frequently Asked Questions

What are the most common Audi S4 problems?

Is the Audi S4 reliable?

How much does it cost to fix common Audi S4 problems?

What is the 2018-2020 Audi S4 Seat-Heater Cable Contact Fault Disables the Passenger Airbag (Recall 21V874 / 74E3)?

What is the 2018-2025 Audi S4 EA839 3.0T Water Pump Internal Seal Failure Leaks Coolant Into the Vacuum System (Class Action)?

What is the 2020-2021 Audi S4 Rear Axle Trailing Arm Eccentric Bolt Lock Nut Can Break from Stress Corrosion (Recall 21V295 / 42L1)?

What is the 2010-2025 Audi S4 Thermostat Housing Failure and Coolant Leak?