Understanding the Volkswagen P1473 Diagnostic Trouble Code
The OBD2 diagnostic trouble code P1473 is a manufacturer-specific code for Volkswagen, Audi, Seat, and Skoda vehicles. In generic terms, it indicates a malfunction within the Secondary Air Injection (SAI) System, specifically related to its electrical control circuit. This system is a critical component of your Volkswagen’s emissions control strategy during a cold start. When the P1473 code is stored, the vehicle’s Engine Control Module (ECM) has detected an electrical fault—such as an open circuit, short to ground, or short to power—in the secondary air injection system’s actuator circuit, most commonly the pump itself or its associated relay.
What is the Secondary Air Injection System and Why Does P1473 Occur?
The Secondary Air Injection (SAI) system is an emissions control device designed to reduce hydrocarbon (HC) and carbon monoxide (CO) emissions during the first 60-90 seconds after a cold engine start. It does this by injecting fresh air from an electric pump into the exhaust manifold, upstream of the catalytic converter. This extra oxygen helps “light off” the catalytic converter faster, allowing it to reach optimal operating temperature and efficiency more quickly.
Core Function of the SAI System
- Cold Start Phase: Activated immediately after starting a cold engine.
- Air Injection: The electric air pump forces ambient air into the exhaust ports or manifold.
- Afterburner Effect: The injected oxygen combines with unburned fuel in the hot exhaust, creating a secondary combustion that raises exhaust gas temperature.
- Catalyst Heating: This rapid temperature increase brings the catalytic converter to its light-off temperature (~400-600°C) much faster, drastically reducing cold-start emissions.
Primary Causes of the P1473 Code
The P1473 code is triggered when the ECM’s expected electrical parameters for the SAI system are not met. The root causes typically fall into these categories:
- Failed Secondary Air Pump: The most common culprit. The electric motor inside the pump can seize, wear out, or suffer internal electrical failure.
- Faulty Secondary Air Pump Relay: This relay provides high-current power to the pump. A stuck open or corroded relay will prevent the pump from receiving voltage.
- Blown Fuse: The SAI pump circuit is protected by a fuse, often in the under-hood fuse box. A blown fuse will immediately disable the circuit.
- Damaged Wiring or Connectors: Corrosion, chafing, or rodent damage to the wiring harness between the ECM, relay, and pump can cause open or short circuits.
- Faulty Combination Valve (Air Injection Valve): While P1473 is primarily electrical, a mechanically seized valve can cause excessive current draw, potentially leading to circuit faults.
- Rare ECM Failure: In uncommon cases, the internal driver circuit within the Engine Control Module itself may fail.
Symptoms and Diagnostic Procedure for P1473
Unlike some codes that cause drivability issues, P1473 symptoms are often subtle but have long-term consequences.
Common Symptoms of a P1473 Fault
- Illuminated Check Engine Light (MIL): The primary and most obvious symptom.
- No Abnormal Engine Performance: The vehicle will typically drive normally; the fault is isolated to the emissions system.
- Possible Failed Emissions Test: Due to higher HC/CO emissions during the cold-start test cycle.
- Audible Clue (if pump fails mechanically): A loud screeching, whining, or rattling noise from the pump (usually located near the front of the engine bay) for a minute after startup.
- No Noise (if electrical failure): Complete silence from the pump area when it should be running.
Step-by-Step Diagnostic Guide
Warning: Always consult vehicle-specific repair information. Safety first: disconnect the battery before probing electrical connections.
Step 1: Preliminary Checks
- Use a professional OBD2 scanner to confirm P1473 is present and clear other codes.
- Perform a visual inspection of the SAI pump, relay, and associated wiring for obvious damage, corrosion, or disconnections.
- Locate and check the SAI pump fuse (refer to owner’s manual or fuse box diagram).
Step 2: Actuating the Secondary Air Pump
Using a capable scan tool, perform an “Output Test” or “Actuator Test” to command the SAI pump on. Listen for the pump to run. If it runs, the issue may be intermittent or related to the valve. If it doesn’t run, proceed to electrical testing.
Step 3: Electrical Circuit Testing
- Power Supply: With the pump commanded on, check for battery voltage (approx. 12V) at the pump’s power supply wire using a multimeter or test light.
- Ground Circuit: Verify the pump’s ground path has continuity and is clean and tight.
- Relay Testing: Swap the SAI relay with an identical one from another circuit (e.g., horn or fan relay) to see if the problem follows the relay.
- Signal from ECM: Using a multimeter or oscilloscope, check for the control signal from the ECM to the relay.
Step 4: Testing the Air Pump and Valve
If power and ground are present at the pump connector but it doesn’t run, the pump is faulty. You can also apply direct battery voltage and ground to the pump terminals (briefly) to confirm. Check the mechanical operation of the combination valve for free movement.
Repair Solutions and Long-Term Considerations
Once the faulty component is identified, repair is generally straightforward. Addressing P1473 is important not just to extinguish the warning light, but to restore your vehicle’s designed emissions performance and prevent potential damage to the catalytic converter from prolonged exposure to unburned fuel.
Common Repairs for P1473
- Replacing the Secondary Air Pump: A common repair. Use OEM or high-quality aftermarket parts. Ensure the new pump includes a new gasket or O-ring.
- Replacing the Relay or Fuse: Always investigate why a fuse blew—it often indicates a short circuit in the pump or wiring.
- Repairing Wiring Harness: Solder and seal any repaired wires; never use twist connectors in the engine bay.
- Replacing the Combination Valve: If seized, it must be replaced. Clean the passages in the cylinder head if clogged with carbon.
Can You Drive with a P1473 Code?
Technically, yes. The vehicle’s drivability and fuel economy are not affected. However, it is not recommended for extended periods for two key reasons:
- Emissions Compliance: Your vehicle will emit pollutants above legal limits, especially during short trips.
- Catalyst Health: The catalytic converter is designed to work in conjunction with a functioning SAI system. Prolonged operation without it can lead to premature catalyst aging or clogging due to excessive carbon deposits.
Preventative Maintenance Tips
While the SAI system is largely non-serviceable, you can minimize issues:
- Address any engine oil leaks promptly, as oil can contaminate and damage the air pump.
- Use high-quality fuel and follow the manufacturer’s maintenance schedule to keep the engine running cleanly.
- During battery replacement or disconnection, ensure the pump’s intake hose is clear of debris before reconnecting power.
In conclusion, the Volkswagen P1473 code is a specific electrical fault within an important cold-start emissions system. While not an emergency, its diagnosis follows a logical path from fuse and relay checks to pump and wiring inspection. Proper repair ensures your VW meets its environmental design standards and maintains the long-term health of its exhaust after-treatment system.