Au7o mascotAu7o
Known IssuesTest Hub demo
  1. Au7o
  2. /
  3. Known Issues
  4. /
  5. Audi
  6. /
  7. S4
Audi · Known Issues

2018 Audi S4 Problems: 3 Known Issues

2018 model year · 107+ owner reports · Updated September 2026

Share:@au7o.io

2018 · All trims · All engines

Choose the year and equipment for your written issues and visual request.

Known IssuesMotorcycle IssuesDTC LookupDrivePricingAboutTermsPrivacyCookiesConsentData rightsCopyrightFeedback
Share:@au7o.io

Vehicle data and repair guidance on this site are compiled with AI assistance and may contain errors. Always verify with your service manual or a qualified mechanic.

Data protection representation

DataRep representative in the United KingdomDataRep representative in the European Union
Au7o · 2026
Built for DIY mechanics. Privacy-first.
Explore free Hub demo
No email neededHow interest is saved

Interest applies to the selected vehicle and configuration; it is not a reservation. Voting stores a first-party identifier for up to 180 days to prevent repeat votes. No account or email is needed. Clearing cookies or using another device may count separately. Privacy

Visual coming soon

Your interest helps us choose what to build next.

Visual Known Issues · Coming soon

$4.99/month plus taxes at launch · No payment today

Preview the XT6 example
Issue summary

According to Au7o's analysis of 107+ owner reports, the 2018 Audi S4 has 3 documented known issues, with 2 rated critical. The most serious are Seat-Heater Cable Contact Fault Disables the Passenger Airbag (Recall 21V874 / 74E3) ($0-$0 repair) and EA839 3.0T Water Pump Internal Seal Failure Leaks Coolant Into the Vacuum System (Class Action) ($1,200-$3,000 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.

In This Article

  • S4 Cooling2
  • S4 Safety/Recalls1
  • Recalls5
  • FAQ
Get Started
Back to top

In This Article

  • Cooling2
  • Safety/Recalls1
  • Recalls5
  • FAQ

All 3 Known Issues

Filter:
ALL YEARS20252024202320222021202020192018201720162015201420132012201120102009200820072006200520042003200220012000

On the 2018-2025 Audi S4, 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 components. Because much of the leak is internal, an owner can lose coolant with nothing visible on the ground, and the first warning may be a low-coolant message or an overheat. Owners and specialists describe it as a when-not-if item on this engine family. Audi has been hit with a class action alleging the pumps are defective across 2.9T and 3.0T EA839 applications, with plaintiffs claiming the automaker knew of the defect since at least November 2018. Note this is a DIFFERENT part and failure mode from the B8 supercharged 3.0T's plastic water pump / thermostat housing.

Common Symptoms

  • Coolant level dropping with no visible external leak
  • Coolant found in the vacuum lines or vacuum reservoir
  • Low-coolant warning message
  • Overheating or fluctuating coolant temperature
  • Sweet coolant smell after driving

How to Fix

No safety recall covers this. The repair is replacement of the water pump (and normally the thermostat housing and any coolant-contaminated vacuum lines and check valves) with the latest revised part. Because the pump sits in the engine V under the intake, labor is significant. Owners on high-mileage cars increasingly replace it preventatively rather than waiting for the internal leak. Check the class-action status - affected owners may have a claim toward the repair cost.

Typical repair cost:$1,200 - $3,000

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
High ConfidenceVerifiedReviewed Aug 2026
Community reported
107 owners

On the 2010-2025 Audi S4 3.0T, 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.

This issue also affects: Audi A5, Audi Q7, Audi S5

Common Symptoms

  • Coolant loss without visible leak
  • Overheating warning
  • Sweet smell from engine bay
  • Coolant puddle under rear of engine
  • Temperature gauge fluctuation
  • Low coolant warning

How to Fix

Replace thermostat housing assembly with updated part. Use OEM or quality aftermarket housing with metal reinforcement.

What you need to fix it

Only diagnosis- and fitment-reviewed repair parts are linked here.

  • Engine Coolant Thermostat Housing Assembly
    Cross-refTHRVG-0013

    Fitment confirmed against the ShowMeTheParts catalog for this vehicle's year and engine.

    eBay

As an Amazon Associate, we earn from qualifying purchases; other part links may also earn au7o a commission. Confirm fitment by VIN before buying.

Typical repair cost:$300 - $800

Research This Issue

Based on 107 owner reports

GoogleRedditYouTubeNHTSA
Community Reported
High Confidence107 owner reportsLast reported by owners Mar 2026Reviewed Mar 2026

On the 2018-2020 Audi S4, 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 deploy in a crash even with an adult occupant in the seat. Audi recalled 208,332 vehicles for this on 10 November 2021 under NHTSA campaign 21V874000, internal code 74E3; the population includes 2018-2020 S4 Sedan along with A4 Sedan/Allroad, A5, S5 and RS5 variants. Owner notification letters went out 7 January 2022.

Common Symptoms

  • Passenger airbag OFF indicator illuminated with an adult in the passenger seat
  • Airbag warning light on
  • Seat heater fault

How to Fix

Free recall remedy. Dealers replace the connecting cable and either the seat heating mat or the entire seat cover with a newly developed shielded connecting cable, at no charge. The warning sign an owner can see is the passenger airbag-off indicator staying lit with an adult passenger seated. Check the VIN on the NHTSA recall lookup or with an Audi dealer - the repair is still available at no cost.

Typical repair cost:$0 - $0

Research This Issue

GoogleRedditYouTubeNHTSA
Community Reported
High ConfidenceVerifiedReviewed Aug 2026
NHTSA Recalls5 recalls

SEAT BELTS:REAR/OTHER:RETRACTOR

Volkswagen Group of America, Inc. (Volkswagen) is recalling certain 2021 Volkswagen ID4, Audi A4 Allroad, A4 Sedan, A5 Cabriolet, A5 Coupe, A5 Sportback, A6 Allroad, A6 Sedan, A7, A8, E-Tron Quattro, E-Tron Sportback Quattro, Q3, Q5, Q5 Sportback, Q7, Q8, RS5 Sportback, RS5 Coupe, RS6 Avant, RS7, RSQ8, S4 Sedan, S5 Cabriolet, S5 Coupe, S5 Sportback, S6 Sedan, S7, S8, SQ5, SQ5 Sportback, SQ7, SQ8, and 2021-2022 S3 Sedan vehicles. The rear seat belt automatic locking retractors may deactivate early, which can prevent the child restraint system from securing properly. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 208, "Occupant Crash Protection."

Campaign #21V60600005/08/2021

TIRES

Volkswagen Group of America, Inc. (Audi) is recalling certain 2019-2021 Audi A5 Sportback, RS5 Coupe, RS5 Sportback, S5 Sportback, 2020-2021 A4 Allroad, A4 Sedan, A5 Cabriolet, A5 Coupe, A6 Allroad, A6 Sedan, A7, A8, Q5, S4 Sedan, S5 Coupe, S5 Cabriolet, S6 Sedan, S7, S8, SQ5, 2021 Q5 Sportback, Q7, Q8, RS6 Avant, RS7, RSQ8, SQ5 Sportback, SQ7, and SQ8 vehicles. The rear axle alignment may not have been inspected after the repairs for Recall 21V-295 (42L1) were performed.

Campaign #22V03400026/01/2022
🔧
A mechanic who knows YOUR exact car
Answers tuned to your year, make, model & trim — not generic advice. Save your garage so it always has the right context.
Get ahead of Audi S4 problems — free
Leave your email and we'll alert you the moment there's a new recall or known issue for your Audi S4. Free, no account needed.

Don't see your problem? Describe your symptoms to get a diagnosis, or get a full repair guide.

Other Audi Models

Audi R830Audi Q329Audi A427Audi A623Audi S722Audi S819

Frequently Asked Questions

What are the most common Audi S4 problems?

According to Au7o's analysis of 107+ owner reports, the 2018 Audi S4 has 3 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), Thermostat Housing Failure and Coolant Leak. Of these, 2 are rated critical and should be addressed promptly.

Is the Audi S4 reliable?

The 2018 Audi S4 has 3 known issues documented across 107+ owner reports. 2 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). 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.

Content on this page was compiled with AI assistance using NHTSA complaints, TSBs, owner reports, and public automotive data. While we strive for accuracy, this information may contain errors. Always verify repair procedures and specifications with your vehicle's service manual or a qualified mechanic.

Data sourced from 107+ owner reports, NHTSA recalls, TSBs, and automotive forums.

SUSPENSION:REAR:AXLE:NON-POWERED AXLE ASSEMBLY

Volkswagen Group of America, Inc. (Audi) is recalling certain 2021 Q7, Q8, Q5 Sportback, SQ5 Sportback, RS6 Avant, RS7, RS Q8, 2020-2021 Audi S6 sedan, Q5, A8, S8, A7, A6 Allroad, A5 Cabriolet, A4 sedan, A4 Allroad, SQ5, S7, A6 sedan, S5 coupe, S4 sedan, S5 Cabriolet, A5 coupe, 2019-2021 RS5 coupe, A5 Sportback, S5 Sportback, RS5 Sportback vehicles. The lock nut on the trailing arm of the rear axle may break due to stress corrosion.

Campaign #21V29500026/04/2021

BACK OVER PREVENTION:DISPLAY FUNCTION

Volkswagen Group of America, Inc. (Volkswagen) is recalling certain 2021 Audi A8, RS7, RS6 Avant, RS5 Sportback, RS5 Coupe, Q8, Q7, Q5 Sportback, S4 Sedan, Q5, A7, A6, A6 Allroad, A5 Sportback, A5 Coupe, A5 Cabrioleet, A4 Sedan, A4 Allroad, E-Tron Sportback Quattro, SQ7, S5 Cabriolet, E-Tron Quattro, SQ8, SQ5 Sportback, SQ5, S8, S7, S6 Sedan, S5 Sportback, S5 Coupe, 2022 E-Tron GT, and 2021-2022 RSQ8 vehicles. Due to a software issue, a blank or black screen may be displayed instead of the rearview camera image when the vehicle is placed in reverse gear. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 111, "Rear Visibility."

Campaign #22V74200005/10/2022

EQUIPMENT:ELECTRICAL:INFOTAINMENT:VIDEO (TOUCH)SCREEN/MONITOR/UNIT

Volkswagen Group of America, Inc. (Audi) is recalling certain 2021-2022 AUDI A8, A6 Allroad, E-TRON Quattro, 2022 S3, RSQ8, RS7, RS6 Avant, Q8, Q7, Q3, E-TRON Sportback Quattro, S5 Cabriolet, E-TRON GT, S5 Sportback, A7, A6, A5 Sportback, A5 Cabriolet, A4, A4 Allroad, A3, S8, SQ7, SQ8, S6, and S4 vehicles. The infotainment main unit may become damaged internally when the vehicle is shut off, resulting in an inoperative rearview camera display the next time the vehicle is started. As such, these vehicles fail to comply with the requirements of Federal Motor Vehicle Safety Standard number 111, "Rear Visibility."

Campaign #22V80600026/10/2022

Enter your VIN at NHTSA.gov to check recalls specific to your vehicle.

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.