Understanding OBD2 Code P1473 in Your Audi
When your Audi’s check engine light illuminates and a scan tool reveals the generic OBD2 code P1473, it indicates a specific fault within the vehicle’s Secondary Air Injection (SAI) System. This system, also known as the Air Pump System, is a critical component of your Audi’s emission control strategy, particularly during a cold start. Code P1473 is defined as “Secondary Air Injection System Pump Relay Circuit Malfunction”. In essence, the Engine Control Module (ECM) has detected an electrical issue with the circuit controlling the secondary air pump’s power relay, preventing the system from activating as designed. This fault can affect performance, increase emissions, and potentially lead to further component damage if left unaddressed.
Technical Causes of the P1473 Fault Code
The P1473 code is triggered when the ECM’s diagnostic routine finds an unexpected voltage level or signal in the relay control circuit. This points to an electrical failure rather than a mechanical blockage. The root causes are typically found in the following components and circuits:
Primary Electrical Culprits
- Faulty Secondary Air Pump Relay: The most common cause. The relay, which provides high-current power to the air pump, can fail internally due to worn contacts, coil failure, or heat damage.
- Failed Secondary Air Pump Motor: A seized or shorted pump motor can draw excessive current, blowing a fuse or causing the relay circuit to fault.
- Blown Fuse or Poor Electrical Connections: A dedicated fuse protects the SAI circuit. Corrosion, damage, or a poor connection at the relay socket, pump connector, or ECM harness can interrupt the signal.
- Damaged Wiring Harness: Chafed, broken, or rodent-damaged wires in the circuit between the ECM, relay, fuse, and pump can create an open or short circuit.
Related System Components
- Defective Vacuum Solenoid (N112 or similar): While P1473 specifically points to the pump circuit, a faulty solenoid that controls the combi valve can cause related issues and should be checked during diagnosis.
- Faulty Engine Control Module (ECM): Rare, but a software glitch or internal driver failure within the ECM itself could prevent proper relay control.
Symptoms and Consequences of Ignoring P1473
You may notice several signs when the Secondary Air Injection System is disabled due to a P1473 code.
Immediate Driver Notices
- Illuminated Check Engine Light (MIL): The primary and most constant symptom.
- Possible Rough Idle on Cold Start: Without the extra oxygen from the SAI system, the engine’s cold-start fuel trim may be less optimal.
- No Abnormal Noise: A key symptom—you will not hear the characteristic loud whirring of the secondary air pump during the first 30-90 seconds after a cold start.
Long-Term Risks
- Increased Emissions: The system’s purpose is to reduce hydrocarbon and carbon monoxide emissions at startup. A failure will cause higher pollutant levels.
- Failed Emissions/Smog Test: The vehicle will likely not pass state or local emissions inspections.
- Potential Catalytic Converter Stress: While not a direct cause of rapid failure, the increased cold-start emissions can contribute to long-term contamination and reduced efficiency of the catalytic converter.
Step-by-Step Diagnostic Procedure for P1473
A systematic approach is essential to correctly diagnose a P1473 code. Always begin with a visual inspection and basic electrical checks before replacing parts.
Phase 1: Preliminary Inspection & Basic Tests
- Visual Check: Inspect the SAI pump (often located near the front bumper or fender well), its wiring, and connectors for obvious damage, corrosion, or disconnection.
- Listen for the Pump: On a cold engine (coolant below ~40°C/104°F), start the engine and listen near the front wheels. You should hear the pump run for a short period. Silence confirms an issue.
- Check the Fuse: Locate and test the SAI pump fuse (consult your Audi’s owner manual or repair guide for location and amperage).
Phase 2: Advanced Electrical Diagnostics
- Test the Air Pump Directly: Disconnect the pump’s electrical connector. Using a fused jumper wire, apply direct 12V power and ground from the battery to the pump terminals. If it doesn’t run, the pump is faulty. If it runs, the problem is upstream.
- Relay Testing: Locate the SAI relay (often in the under-hood relay plate). Swap it with an identical, non-critical relay (e.g., horn or fog light relay). Clear the code and test. If P1473 returns, the relay is likely not the issue.
- Circuit & Signal Verification: With a digital multimeter or oscilloscope, back-probe the relay control wire from the ECM. You should see a 12V signal (or a pulsed ground signal, depending on design) for ~90 seconds after a cold start. No signal points to an ECM or wiring issue.
Repair Solutions and Professional Considerations
Once the faulty component is identified, repairs can be straightforward. However, Audi-specific practices must be considered.
Common Repairs and Parts Replacement
- Replacing the Secondary Air Pump: A common repair. Use quality OEM or OEM-equivalent parts. Ensure the new pump includes a new gasket for the connection to the combi valve.
- Replacing the Relay or Fuse: Simple fixes. Always replace a blown fuse with one of the exact same amperage.
- Repairing Wiring: Solder and heat-shrink any repaired wires. Never use twist connectors in automotive engine bay applications.
Audi-Specific Notes and Software
- ECM Coding/Adaptation: On some newer Audi models, replacing the secondary air pump may require a basic setting adaptation or coding procedure using a professional scan tool like VCDS, ODIS, or an equivalent capable of VW/Audi diagnostics.
- Check for Technical Service Bulletins (TSBs): Some Audi models have known issues with SAI system components or related software updates. A dealer or specialist can check for relevant TSBs.
- Full System Check: After repairing the P1473 circuit, it is advisable to check the function of the combi valve and vacuum lines to ensure the entire SAI system is operational.
Successfully diagnosing and repairing an OBD2 code P1473 restores your Audi’s emission system integrity, ensures compliance with environmental regulations, and maintains optimal engine management during the critical warm-up phase. Following a logical diagnostic path saves time and money by preventing unnecessary part replacement.