1. What is P0037 in Audi A4L?

The P0037 OBD-II code stands for HO2S Heater Control Circuit Low (Bank 1 Sensor 2). For the Audi A4L B9 (2019-2024)—a top-selling European executive sedan—this code targets the rear oxygen (HO2S) sensor in its 2.0T EA888 Gen3 engine, standard in 45 TFSI Quattro, 40 TFSI Luxury, and S line trims (paired with 7-speed S tronic transmission).

The A4L’s "Bank 1 Sensor 2" is the post-catalytic converter oxygen sensor (mounted on the left exhaust downpipe, 6 inches downstream of the cat). Its heater circuit warms the sensor to 600°C in 30 seconds—critical for accurate exhaust gas monitoring and emissions compliance. P0037 triggers when the ECU detects heater circuit voltage <0.9V (normal: 11–14V) or resistance >10Ω—indicating a faulty sensor, damaged wiring, or ECU power supply issues.

Audi A4L Specific Note: This code is widespread in 2020-2023 45 TFSI Quattro models, per Audi Technical Service Bulletin (TSB) 21-07-02. The EA888’s turbocharged exhaust generates extreme heat; frequent short trips (under 5 miles) prevent the sensor heater from fully cycling, leading to premature coil burnout.

2. Common Causes of P0037 in 2019-2024 A4L

P0037 in Audi A4L EA888 models stems from rear oxygen sensor heater circuit failures—below are real-world cases diagnosed with the ICARZONE UR800:

• Faulty Rear O2 Sensor (2021 A4L 45 TFSI Quattro): An owner with 55,000 miles reported a "Check Engine" light and rough idle. The UR800’s O2 Sensor Heater Test showed 0.6V (normal: 11–14V) and resistance 15Ω. Replacing the sensor with OEM #06K906262B (per TSB 21-07-02) fixed P0037.
• Damaged Sensor Wiring (2020 A4L 40 TFSI Luxury): A Luxury trim owner’s P0037 reappeared after sensor replacement. The UR800’s Circuit Continuity Test found a broken wire—insulation melted by exhaust heat (harness runs near the turbo downpipe). Repairing with heat-resistant wire (#Dorman 10501) restored voltage.
• ECU Power Supply Issue (2019 A4L 45 TFSI S line): An S line owner’s P0037 persisted after wiring repairs. The UR800’s ECU Voltage Test showed 9V to the sensor circuit (normal: 12V). Replacing the ECU fuse #F28 (15A) stabilized power and cleared the code.
• Corroded Sensor Connector (2022 A4L 45 TFSI Quattro): A Quattro owner’s P0037 occurred after heavy rain. The UR800’s Connector Test detected corrosion in the 4-pin plug. Cleaning with electrical contact cleaner (#CRC 05110) and applying dielectric grease fixed the circuit.

3. Key Symptoms of P0037 in A4L 45 TFSI

P0037 symptoms in the Audi A4L focus on sensor heater failure and emissions performance—watch for these signs that signal circuit issues:

4. Audi A4L Trims/Engines Prone to P0037

Audi service data highlights these 2019-2024 A4L configurations with the highest P0037 occurrence rates (all EA888 Gen3 engines):

5. Diagnose P0037 with ICARZONE UR800

Diagnose P0037 in your Audi A4L EA888 accurately with the UR800’s Audi-specific oxygen sensor tools. Follow these steps (engine off, key in "ON" position; ensure exhaust is cool):

Case Example: A 2021 A4L 45 TFSI Quattro failed Step 2 (0.7V) and Step 5 (TSB 21-07-02 eligible). The UR800’s Component Location Tool guided sensor access (left exhaust downpipe, below the catalytic converter). Replacing the sensor fixed P0037—verified by test drive (restored MPG, smooth idle).

6. How to Fix P0037 in Audi A4L

Resolve P0037 in your A4L with these UR800-verified solutions—tailored to the EA888 engine’s exhaust system:

1. Replace Rear Oxygen Sensor (Most Common Fix for TSB 21-07-02)

1. Confirm sensor failure via UR800’s Step 3. Raise the A4L with jack stands (secure to frame rails) and locate the rear O2 sensor: Left exhaust downpipe, 6 inches downstream of the catalytic converter (4-pin connector, 1 hex nut).
2. Disconnect the sensor’s electrical connector (press the release tab) and spray penetrating oil on the hex nut (let sit 5 minutes to loosen rust).
3. Remove the sensor with a 22mm oxygen sensor socket—turn counterclockwise. Inspect the threads for damage (clean with a wire brush if needed).
4. Install an OEM rear O2 sensor:
   • 2019-2021 A4L: #06K906262B
   • 2022-2024 A4L: #06K906262C (heat-resistant heater coil)
   Apply anti-seize compound to the sensor threads (avoid getting on the tip).
5. Tighten the sensor to 30 ft-lbs, reconnect the connector, and lower the A4L. Clear P0037 with UR800 and run a Heater Test to confirm 11–14V.

2. Repair Damaged Sensor Wiring

1. Confirm wiring issue via UR800’s Step 4. Trace the sensor harness from the rear O2 sensor to the ECU (runs along the left frame rail, near the exhaust).
2. Identify melted or frayed insulation—cut out 1 inch of damaged section (use wire cutters) and strip 1/4 inch of insulation from both ends.
3. Splice new 18-gauge heat-resistant wire (#Dorman 10501) using heat-shrink butt connectors. Crimp connectors and apply heat to seal (no exposed wire).
4. Secure the repaired harness to the frame rail with heat-resistant zip ties (avoids contact with hot exhaust). Reconnect the sensor and ECU connectors.
5. Retest continuity with UR800 (Step 4) and clear P0037. Test drive to confirm no voltage drops during acceleration.

3. Fix ECU Power Supply (Fuse Replacement)

1. Confirm power issue via UR800’s Step 2 (low voltage). Locate the A4L’s interior fuse box: Driver’s side dashboard, behind the knee panel.
2. Remove the fuse box cover and find fuse #F28 (15A)—labeled "O2 Sensor Heater" in the diagram.
3. Check the fuse for a broken filament—replace with a new 15A mini fuse (#Bussmann ATC15).
4. Reinstall the fuse box cover and retest sensor heater voltage with UR800 (Step 2) — confirm 11–14V.
5. Clear P0037 with UR800 and test drive to ensure stable circuit performance.

7. P0037 Repair Costs & Maintenance Tips

P0037 repair costs for the Audi A4L EA888 vary by cause. Use this table to budget:

Maintenance Tips for Audi A4L Owners

• 45 TFSI Quattro (urban drivers): Replace the rear O2 sensor every 80,000 miles (preventive) — use OEM #06K906262C for 2022+ models to avoid TSB 21-07-02 burnout.
• Inspect sensor wiring during oil changes—wrap exposed sections with heat-resistant tape (#3M 33+) to protect against exhaust heat (critical for S line trims).
• Avoid short trips (under 5 miles) 3+ times weekly—let the engine run for 2 minutes after startup to warm the sensor heater fully.
• Clean the rear O2 sensor connector annually with electrical contact cleaner—apply dielectric grease to prevent moisture corrosion (key for Premium trims in wet climates).
• Perform the UR800’s O2 Sensor Health Check every 15,000 miles — monitor heater voltage and resistance to catch issues before P0037 triggers.

8. Audi A4L-Specific FAQs