Understanding the BMW P1475 Fault Code
The OBD2 diagnostic trouble code (DTC) P1475 is a manufacturer-specific code for BMW vehicles, indicating a problem within the Secondary Air Injection (SAI) system. Specifically, it points to a malfunction in the electrical circuit controlling the SAI pump’s relay. This system is a critical part of your BMW’s emissions control strategy during a cold start. When the P1475 code is stored, the vehicle’s Engine Control Module (ECM or DME) has detected an unexpected voltage, resistance, or signal in the relay circuit for the secondary air pump. Ignoring this code can lead to failed emissions tests, reduced engine performance in certain conditions, and potential damage to other components like the catalytic converter.
What is the Secondary Air Injection (SAI) System?
The Secondary Air Injection system, often called the air pump system, is an emissions control device. Its sole purpose is to reduce hydrocarbon (HC) and carbon monoxide (CO) emissions during the first 30-90 seconds after a cold engine start. It does this by injecting fresh air from an electric pump into the exhaust manifold or cylinder head exhaust ports. This extra oxygen helps “burn off” unburned fuel in the exhaust, rapidly heating up the catalytic converter to its efficient operating temperature. Once the engine is warm, the system shuts off.
The Role of the Air Pump Relay
The air pump relay is the high-current switch commanded by the DME. The electric air pump draws significant amperage (often 20-40 amps), which is too much for the DME to handle directly. The relay acts as an intermediary: a low-current signal from the DME energizes the relay’s coil, which then closes a high-current circuit to power the air pump. A fault in this relay or its wiring—open circuits, short circuits, or excessive resistance—triggers code P1475.
Symptoms of a BMW P1475 Code
You may notice one or more of the following symptoms when code P1475 is active in your BMW. The most common is the illumination of the Check Engine Light (MIL).
- Check Engine Light (MIL) Illuminated: This is the primary and most frequent indicator.
- Rough Idle on Cold Start: The engine may idle roughly for the first minute as the emissions are not being optimally managed.
- Failed Emissions Test: Elevated HC and CO levels during the idle test are a direct consequence of a non-functional SAI system.
- Audible Clicking or No Sound from Pump: On a cold start, you should hear the distinct sound of the air pump running near the front of the engine bay for about a minute. Silence or a rapid clicking (relay chattering) indicates a problem.
- Other Related Codes: You may also find codes like P0410 (Secondary Air Injection System Malfunction) or P0411 (Incorrect Flow Detected).
Diagnosing and Fixing the P1475 Code on Your BMW
Diagnosis requires a systematic approach, starting with the simplest and most common causes. You will need a basic set of tools and a diagnostic scan tool or a quality OBD2 code reader.
Step 1: Preliminary Visual and Auditory Inspection
Start with the engine cold. Have an assistant start the engine while you listen in the engine bay. You should immediately hear the secondary air pump run loudly for 60-90 seconds. If it’s silent, the pump, relay, or wiring is faulty. Visually inspect the pump (usually near the front bumper or strut tower), its hoses for cracks/disconnections, and the wiring harness for obvious damage or corrosion.
Step 2: Testing the Secondary Air Pump Relay
The relay is typically located in the main power distribution box (fuse/relay box) in the engine bay. Consult your owner’s manual or a repair database for its exact location (e.g., Relay K6302).
- Swap Test: The easiest test is to swap the air pump relay with an identical relay from another circuit (like the horn or fog light relay). Clear the code, perform a cold start, and see if the code returns or if the pump now runs. If the problem moves, the relay is bad.
- Bench Test: Using a multimeter, test the relay’s coil resistance (typically 70-90 ohms) and check for continuity across the switched contacts when the coil is energized with 12V.
Step 3: Checking Power and Ground at the Pump
If the relay is good, the problem lies in the wiring or the pump itself. With the relay removed, check for constant battery voltage (12V) at one of the relay socket terminals that feeds the pump. Check for a good ground at the pump’s connector. Finally, with the relay installed and the engine started cold, use a multimeter or a test light to verify that the pump is receiving the commanded 12V+ signal.
Step 4: Inspecting the Air Pump and Related Components
A faulty pump itself can cause a circuit malfunction by drawing excessive current (creating a short) or having an open internal circuit.
- Direct Power Test: Apply 12 volts directly to the pump terminals (observing polarity). A functioning pump will run loudly. If it doesn’t run or runs weakly, the pump is defective.
- Check Valve: A failed one-way check valve in the air hose can allow hot exhaust gases or moisture back into the pump, causing it to seize or corrode. Inspect and replace if faulty.
- Hoses and Connections: Cracked, melted, or disconnected hoses will cause the system to fail flow tests but may not directly cause P1475 unless debris has damaged the pump.
Common Repairs and Associated Costs
Repair costs can vary widely based on the specific BMW model and whether you use OEM, aftermarket, or used parts.
Replacing the Air Pump Relay
This is the most cost-effective repair. An aftermarket relay typically costs $15 – $40. It’s a simple DIY job requiring no special tools beyond possibly a plastic trim removal tool to access the relay box.
Replacing the Secondary Air Pump
This is the most common mechanical repair. Aftermarket pumps range from $100 to $300, while genuine BMW pumps can cost $400 to $700+. Labor adds 1-2 hours ($100-$300). The pump is usually accessible but may require removal of the front bumper or wheel liner on some models (e.g., E60, E90).
Repairing Wiring Harness or Connectors
If the issue is a broken wire, corroded connector, or damaged fuse, the cost is minimal for parts ($5 – $50) but requires skilled diagnostic time to locate the fault. Proper solder and heat-shrink repairs are essential.
Professional Diagnosis and Repair
If DIY diagnosis is inconclusive, a professional BMW specialist will perform the above steps systematically, potentially using a scope to monitor relay control signals. Expect 1 hour of diagnostic time ($100-$200) plus the cost of the required part and installation labor. A full pump and relay replacement at a dealer or independent shop can range from $500 to over $1,200.
Conclusion: Code P1475 on your BMW is a specific electrical fault in the secondary air injection system’s control circuit. While it doesn’t usually cause immediate drivability issues, it is an important emissions-related fault that should be addressed. Starting with the simple relay swap test often leads to a quick and inexpensive fix. A methodical diagnostic approach—checking the relay, power, ground, and finally the pump itself—will reliably identify the root cause, whether it’s a $20 relay or a more expensive air pump assembly.