Understanding the BMW P1470 Fault Code
The OBD2 diagnostic trouble code P1470 is a manufacturer-specific code for BMW vehicles, indicating a fault within the Secondary Air Injection (SAI) system. In generic terms, it translates to “Secondary Air Injection System Flow Fault.” This system is a critical component of your BMW’s emissions control strategy, specifically during a cold engine start. Its primary function is to reduce harmful exhaust emissions (hydrocarbons and carbon monoxide) by injecting fresh air into the exhaust manifold immediately after starting the engine. This extra oxygen helps the hot exhaust gases ignite unburned fuel, rapidly increasing the temperature of the catalytic converter to its optimal operating efficiency. A P1470 code signals that the Engine Control Module (DME) has detected an insufficient or non-existent airflow from this system.
How the Secondary Air Injection System Works
The system operates for a very short period, typically 30 to 90 seconds after a cold start (engine coolant temperature below a specific threshold, often 40-50°C). The DME activates the system by:
- Engaging the Secondary Air Pump (SAP) Relay: This provides power to the electric air pump, which begins to draw in fresh air.
- Opening the Secondary Air Injection Valve: This valve, often vacuum-operated, opens a pathway from the pump to the exhaust ports or manifold.
The DME monitors the system’s operation indirectly, usually by observing the signal from the pre-catalytic converter oxygen sensors. A properly functioning SAI system will cause the oxygen sensor readings to go lean (high oxygen content) for a brief period after startup. If the DME does not see this expected change, it will log code P1470.
Common Symptoms and Causes of P1470 in BMW
While the Check Engine Light (CEL) or Service Engine Soon light is the most universal symptom, a P1470 code can manifest in several ways. It’s important to note that drivability is often unaffected, as the system only works for a short time after a cold start.
Primary Symptoms
- Illuminated Check Engine Light (MIL).
- Possible “increased emissions” warning on the instrument cluster.
- Rough idle or slight hesitation only during the first minute after a cold start.
- Abnormally loud whirring or grinding noise from the engine bay (if the air pump is failing mechanically).
- No unusual symptoms at all – the code may be stored without noticeable drivability issues.
Root Causes of the Fault
The P1470 code points to a lack of airflow, which can be caused by failures in several components:
- Failed Secondary Air Pump: The most common culprit. The electric motor can burn out, the impeller can break, or the pump can become clogged with debris.
- Faulty Secondary Air Injection Valve: This valve can stick shut, fail to open due to a damaged diaphragm, or become clogged with carbon deposits.
- Vacuum Supply Issues: The valve is typically vacuum-actuated. Cracked, brittle, or disconnected vacuum lines will prevent the valve from opening.
- Electrical Problems: A blown fuse, faulty relay, corroded wiring, or bad connector to the air pump or valve.
- Blocked or Cracked Hoses: The air hose from the pump to the valve, or from the valve to the exhaust, can crack, leak, or become internally obstructed.
- Exhaust Leaks Upstream: A significant leak before the oxygen sensor can skew readings and trick the DME.
Step-by-Step Diagnostic Procedure for P1470
A systematic approach is key to correctly diagnosing a P1470 code. Avoid the temptation to just replace the air pump immediately; testing the components first can save time and money.
Initial Checks and Visual Inspection
Begin with a thorough visual examination. With the engine cold, inspect the entire secondary air system pathway:
- Locate the secondary air pump (usually near the front bumper, firewall, or in the wheel well). Listen carefully for any unusual noises when a helper starts the cold engine.
- Trace all associated rubber hoses and vacuum lines for cracks, disconnections, or soft, spongy spots.
- Check the electrical connector at the pump and valve for corrosion or damage.
- Inspect the pump’s intake filter (if equipped) for blockage.
- Verify the relevant fuses (check your owner’s manual for location).
Testing the Secondary Air Pump
You can test the pump’s operation directly. Using a scan tool with bi-directional controls, command the secondary air pump ON. You should hear it run loudly. If it doesn’t:
- Check for battery voltage (typically 12V) at the pump’s electrical connector with the pump commanded ON.
- If voltage is present but the pump doesn’t run, the pump motor is faulty.
- If no voltage is present, diagnose the circuit back through the relay, fuse, and DME control signal.
Testing the Vacuum System and Valve
The valve must open to allow airflow. With the pump commanded ON:
- Feel the valve – you should feel it click open.
- Disconnect the vacuum hose from the valve and check for strong vacuum with a vacuum gauge when the system is activated.
- Apply external vacuum (using a hand pump) to the valve’s vacuum port. It should hold vacuum and open. If it doesn’t, the diaphragm is ruptured.
- With the valve removed, check for carbon blockage in the ports.
Repair Solutions and Important Considerations
Once the faulty component is identified, repair is generally straightforward. However, there are critical factors to consider for a lasting fix.
Component Replacement and Final Verification
Replace the identified faulty part with a quality OEM or reputable aftermarket component. When reinstalling:
- Replace any brittle or questionable vacuum lines and air hoses.
- Ensure all connections are tight and secure.
- Clear the fault code with your OBD2 scanner.
- Perform a cold start test cycle. The engine must be completely cold (ideally left overnight). Start the engine and observe if the code returns. This is the only way to verify the repair, as the system only operates under these specific conditions.
The Risks of Ignoring Code P1470
While your BMW may drive normally, ignoring a P1470 code has consequences:
- Failed Emissions Test: Your vehicle will almost certainly fail a state or local emissions inspection.
- Increased Emissions: The vehicle will emit higher levels of HC and CO during cold starts.
- Potential Catalytic Converter Damage: While rare, consistently poor warm-up can lead to premature catalyst aging or clogging over a very long period.
- Masking Other Problems: A persistent check engine light may prevent you from noticing new, more serious fault codes.
Diagnosing and repairing a BMW P1470 code requires a methodical approach focused on the vacuum and electrical controls of the Secondary Air Injection system. By following this technical guide, you can accurately identify whether the issue lies with the pump, the valve, the vacuum supply, or the wiring, leading to an efficient and correct repair.