Understanding OBD2 Code P1473 in Your MINI
When your MINI’s check engine light illuminates and a scan tool reveals the Diagnostic Trouble Code (DTC) P1473, it points directly to a fault within the Secondary Air Injection System (SAIS). This system is a critical component of your vehicle’s emission control strategy, specifically during a cold start. Code P1473 is defined as “Secondary Air Injection System Pump Relay Circuit Malfunction.” In simpler terms, the vehicle’s Engine Control Module (ECM) has detected an electrical issue with the circuit controlling the secondary air pump’s power relay. This prevents the system from activating, leading to increased emissions and potential long-term engine component damage.
What is the Secondary Air Injection System (SAIS)?
The SAIS is an emissions control device designed to reduce hydrocarbon (HC) and carbon monoxide (CO) emissions during the first 30-90 seconds after a cold engine start. When the engine and catalytic converter are cold, their efficiency is low. The system works by injecting fresh air from an electric air pump directly into the exhaust ports or exhaust manifold. This extra oxygen helps “burn off” unburned fuel in the exhaust, raising the temperature of the exhaust gases and allowing the catalytic converter to reach its optimal operating temperature much faster.
How the SAIS Circuit Works and Triggers P1473
The system’s operation is managed by the ECM. Upon a cold start, the ECM checks various parameters (coolant temperature, engine load, etc.). If conditions are met, it activates a vacuum solenoid that opens a combination valve. Simultaneously, it sends a signal to the SAIS pump relay, which provides high-current power to the electric air pump. Code P1473 is set when the ECM detects an unexpected voltage level or an open/short circuit in the control side of this relay circuit. It does not necessarily mean the pump itself is dead, but that the command to turn it on cannot be properly executed.
Symptoms and Causes of a P1473 Fault Code
Ignoring a P1473 code can lead to failed emissions tests and accelerated wear on your catalytic converter. Recognizing the symptoms is the first step toward a repair.
Common Symptoms of P1473
- Illuminated Check Engine Light (MIL): The primary and most common indicator.
- Rough Idle on Cold Start: The engine may stumble for a few seconds after starting.
- Increased Exhaust Emissions: You may notice a stronger fuel smell from the exhaust on cold mornings.
- Lack of Performance Symptoms: Usually, there is no direct drivability issue, but the ECM may run a slightly richer fuel mix.
- Possible Other Codes: Codes like P0410 (Secondary Air Injection System Malfunction) or P0411 (Incorrect Flow Detected) may also be present.
Root Causes of DTC P1473
- Failed Secondary Air Pump Relay: The relay itself is a common point of failure, with internal contacts burning out.
- Faulty Secondary Air Pump: The electric motor inside the pump can seize or fail, often drawing excessive current that damages the relay.
- Open or Shorted Wiring: Damaged, corroded, or broken wires in the pump or relay control circuit.
- Blown Fuse: The SAIS circuit is protected by a specific fuse, which may blow due to a pump seizure or short circuit.
- Poor Electrical Connections: Corrosion at the relay socket, pump connector, or ground points.
- Faulty Vacuum Solenoid or Combination Valve: While these more commonly cause flow-related codes, a severe vacuum leak could affect system monitoring.
Diagnostic and Repair Procedure for MINI P1473
A systematic approach is key to correctly diagnosing and fixing a P1473 code. Always begin with the simplest and most cost-effective checks.
Step 1: Preliminary Checks and Visual Inspection
Start by locating the main components. In most MINI models (R50, R53, R56), the secondary air pump is typically mounted low in the engine bay, often behind the front bumper or near the wheel well. The relay and fuse are usually in the engine bay electronic box (E-box).
- Locate and inspect the SAIS fuse. Replace if blown. Caution: If the new fuse blows immediately, a short circuit is present.
- Visually inspect all wiring harnesses connected to the pump, relay, and solenoid for chafing, burns, or corrosion.
- Check the pump’s intake hose for blockages (leaves, debris) which can cause the pump to overwork and fail.
Step 2: Testing the Secondary Air Pump and Relay
With a multimeter, you can perform basic tests:
- Relay Test: Swap the SAIS relay with an identical, known-good relay from another slot (e.g., horn or fan relay). Clear the code and perform a cold start. If the code doesn’t return, the original relay is faulty.
- Pump Test (Direct Power): Disconnect the electrical connector from the air pump. Apply direct 12-volt power and ground from the battery to the pump terminals. A functioning pump will run loudly. If it doesn’t run or sounds labored, the pump is faulty. Never run the pump dry for more than a few seconds.
- Circuit Test: Check for battery voltage at the pump’s power supply wire (with ignition on) and for a proper ground.
Step 3: Advanced Diagnostics and Final Repair
If components test good, deeper electrical diagnosis is needed.
- Use a scan tool with bi-directional controls to command the SAIS relay “ON.” Listen for an audible click from the relay.
- With a 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) when the system is commanded on during a cold start.
- Check the resistance of the vacuum solenoid and the operation of the combination valve. A stuck-closed valve can cause backpressure that strains the pump.
The most common repair is replacing the secondary air pump and its relay as an assembly, as a failing pump often takes the relay with it. Always use quality OEM or reputable aftermarket parts.
Cost, Prevention, and Long-Term Implications
Addressing P1473 promptly protects your investment and keeps your MINI running cleanly.
Estimated Repair Costs
Costs vary widely based on model year and labor rates:
- DIY Repair (Pump & Relay): $150 – $400 for parts.
- Independent Shop: $350 – $700+ (parts and labor).
- MINI/BMW Dealer: $600 – $1,200+.
The pump itself is the most expensive component. Labor can be moderate to high if the pump is difficult to access.
Why You Should Not Ignore Code P1473
While the car may seem to run fine, a disabled SAIS has direct consequences:
- Catalytic Converter Damage: The primary catalyst works harder to clean emissions when cold, leading to premature clogging or meltdown. Cat replacement costs are exponentially higher than fixing the SAIS.
- Failed Emissions Testing: Your vehicle will not pass a tailpipe or OBD2 emissions test with this active code.
- Reduced Environmental Efficiency: Your MINI will emit significantly higher levels of pollutants during cold-start phases.
By understanding and addressing OBD2 code P1473 with a structured diagnostic approach, you can restore your MINI’s emission system health, ensure it passes inspection, and prevent costly damage to the catalytic converter.