P0491 on Audi: Symptoms, Causes & Fix
Official technical diagnostic wire for fault code P0491 specifically affecting Audi vehicles (A4, A6, Q5, Q7, A3).
Select Your Audi Model for P0491:
1. Common Symptoms on Audi Vehicles
When Audi Engine Control Modules (ECM) trigger fault code P0491, drivers typically report:
2. Root Causes on Audi Engines
Historical diagnostic claims across Audi engines point to the following failure distribution:
3. Step-by-Step Fix Protocol for Audi
Connect an OBD-II scan tool and record freeze frame sensor telemetry for code P0491 to note engine RPM, load, and voltage when the fault triggered. on Audi engines.
Inspect the electrical connector and wiring harness related to P0491 for chafing, corrosion, moisture, or pin push-out. on Audi engines.
Measure circuit voltage supply (12V B+ or 5V reference) and sensor/actuator resistance according to factory repair manual specifications. on Audi engines.
Install a new OEM-grade replacement part, torque fasteners to factory spec, and ensure electrical locking tabs click firmly. on Audi engines.
Clear all stored DTCs from vehicle memory and perform an OBD-II drive cycle to confirm the diagnostic monitor resets to 'Ready'. on Audi engines.
Equipment for Diagnosing Audi (P0491)
Audi OEM Replacement Sensor
Direct-fit replacement assembly engineered to OEM tolerances for Audi.
AstroAI Auto-Ranging Digital Multimeter
Essential for testing 0.1V–5.0V sensor reference signals, ground continuity (<0.20Ω), and harness resistance.
BlueDriver Bluetooth Pro OBDII Scan Tool
Reads and clears enhanced codes (ABS, Airbag, Transmission, Engine) & live freeze-frame telemetry on phone.
4. Audi P0491 Frequently Asked Questions
What does code P0491 mean on a Audi?
On Audi vehicles, P0491 indicates that the Engine Control Module (ECM) detected secondary air injection system insufficient flow (bank 1). This typically points to Clogged secondary air ports in cylinder head with carbon or Defective Bank 1 air check valve.
Can I continue driving my Audi with code P0491?
Yes. Cold start emissions system fault. Because this code carries a Low severity rating on Audi powertrains, we recommend scanning live data values promptly to prevent secondary damage.
How much does it cost to fix code P0491 on a Audi?
Estimated DIY parts cost ranges from $180 - $850, while professional shop repairs at an authorized Audi dealership or independent specialist typically range from $180 to $380 including diagnostic labor.