Understanding OBD2 Code P1475: The EVAP Leak Detection Pump Circuit
When your vehicle’s check engine light illuminates and an OBD2 scanner retrieves the diagnostic trouble code (DTC) P1475, it indicates a specific fault within the Evaporative Emission Control (EVAP) system. This code is formally defined as “Evaporative Emission Control System Leak Detection Pump Circuit”. Unlike generic EVAP leak codes (like P0442), P1475 is a manufacturer-specific code, most commonly associated with Chrysler, Dodge, Jeep, and Volkswagen/Audi vehicles. It points directly to an electrical or functional problem with the Leak Detection Pump (LDP) itself or its control circuit, which is a critical component for the vehicle’s self-test of the fuel vapor containment system.
What is the EVAP System and the Leak Detection Pump?
The EVAP system is designed to prevent fuel vapors from the gas tank from escaping into the atmosphere. It captures these vapors in a charcoal canister and later purges them into the engine to be burned. The Leak Detection Pump (LDP) is a smart component used in many modern vehicles to actively test the integrity of this sealed system. During a self-test (usually performed after a cold start under specific driving conditions), the LDP pressurizes the EVAP system with air. The vehicle’s Powertrain Control Module (PCM) then monitors pressure decay to determine if a leak is present. Code P1475 is set when the PCM detects an unexpected voltage, resistance, or operational fault in the LDP’s electrical circuit.
Common Symptoms and Causes of a P1475 Code
While a P1475 code may not always cause drivability issues, it will prevent the EVAP system from completing its self-diagnosis, potentially masking a larger fuel vapor leak. Recognizing the symptoms and understanding the root causes is the first step in effective troubleshooting.
Primary Symptoms of Code P1475
- Illuminated Check Engine Light (MIL): This is the most common and often the only noticeable symptom.
- Failed Emissions Test: The vehicle will not pass a state or local emissions inspection with an active EVAP system code.
- Possible Fuel Odor: If the LDP fault is related to a mechanical failure, it may not seal properly, allowing fuel vapors to escape.
- Other EVAP Codes: You may also find related codes like P0442 (small leak) or P0455 (large leak) if the LDP failure prevents proper leak testing.
Root Causes of the P1475 Diagnostic Trouble Code
- Faulty Leak Detection Pump (LDP): The pump motor can fail, or internal valves can stick, rendering the unit inoperative.
- Damaged Wiring or Connectors: Corrosion, chafing, or rodent damage to the wiring harness connecting the LDP to the PCM.
- Poor Electrical Connections: Loose, corroded, or oxidized pins in the LDP or PCM connectors.
- Blown Fuse or Fusible Link: A dedicated fuse supplying power to the LDP circuit may be blown.
- Defective PCM (Rare): While uncommon, a failure in the PCM’s driver circuit that controls the LDP can trigger this code.
Step-by-Step Diagnosis and Repair for P1475
Diagnosing a P1475 code requires a methodical approach, combining visual inspection, electrical testing, and functional checks. Always consult your vehicle’s specific service manual for wiring diagrams and specifications.
Step 1: Preliminary Visual Inspection
Begin with a thorough visual check. Locate the Leak Detection Pump (common locations include near the charcoal canister, behind a rear wheel well, or under the vehicle). Inspect the pump for physical damage, cracks, or disconnected hoses. Examine the electrical connector for corrosion, bent pins, or moisture. Trace the wiring harness back towards the PCM, looking for any obvious damage.
Step 2: Electrical Circuit Testing
Using a digital multimeter (DMM), perform key electrical tests with the connector disconnected:
- Power Supply: Check for battery voltage (typically 12V) at the power wire with the ignition ON.
- Ground Circuit: Verify continuity between the ground pin and a known good chassis ground. Resistance should be very low (less than 5 ohms).
- Signal/Control Circuit: Test for continuity on the control wire from the LDP connector back to the PCM pin. Check for shorts to power or ground.
Step 3: Testing the Leak Detection Pump Itself
If the circuit tests good, the pump itself is suspect. You can perform a bench test. Apply direct battery voltage and ground to the pump terminals (observe polarity). A functioning LDP should activate audibly. You can also check its internal filter for clogging, which is a common issue on some Chrysler models. Use an advanced scan tool to command the LDP ON and OFF while monitoring its current draw; an abnormal reading indicates a failing pump.
Step 4: Clearing the Code and Verification
After repairs (replacing the LDP, repairing wiring, cleaning connectors), clear the P1475 code with your scan tool. The vehicle will need to go through a complete drive cycle to run the EVAP monitor self-test. Use your scanner to confirm that all monitors, especially the EVAP monitor, complete successfully and that the code does not return.
Technical Considerations and Professional Advice
Code P1475 is a circuit code, not a leak code. It’s crucial to diagnose the circuit fault before assuming there’s a physical vapor leak. Misdiagnosis can lead to unnecessary parts replacement, such as gas caps or canisters.
When to Seek Professional Help
If you lack advanced diagnostic tools (like a bi-directional scan tool) or are uncomfortable with electrical testing, seeking a professional mechanic is wise. They have access to manufacturer-specific technical service bulletins (TSBs) that may identify known issues and updated repair procedures for your specific make and model.
Importance of a Proper Repair
Ignoring a P1475 code is not advisable. A malfunctioning EVAP system can increase hydrocarbon emissions, potentially cause a fuel smell, and will cause your vehicle to fail mandatory emissions testing. Proper diagnosis and repair ensure your vehicle runs cleanly and efficiently while keeping you compliant with environmental regulations.
By following this structured diagnostic approach, you can effectively address the underlying cause of OBD2 code P1475, restore your EVAP system to full functionality, and extinguish that check engine light for good.