Understanding the Chrysler P1479 OBD2 Diagnostic Trouble Code
The P1479 diagnostic trouble code (DTC) is a manufacturer-specific code primarily associated with Chrysler, Dodge, and Jeep vehicles. It is directly related to the vehicle’s Evaporative Emission Control (EVAP) system. In simple terms, this code indicates a fault in the circuit of the Leak Detection Pump (LDP) switch. The EVAP system’s primary function is to capture and store fuel vapors from the fuel tank, preventing them from escaping into the atmosphere, and then purging them into the engine to be burned during normal combustion. The Leak Detection Pump is a critical self-test component within this system.
What is the Leak Detection Pump (LDP)?
The Leak Detection Pump is not a traditional fuel pump. It is an electrically operated pump used by the Powertrain Control Module (PCM) to perform a self-test on the integrity of the EVAP system. During a specific drive cycle, the PCM activates the LDP to pressurize the EVAP system slightly. The LDP contains an internal diaphragm and a switch. The PCM monitors the state of this internal switch to determine if the pump is operating correctly and if the system can hold pressure, indicating no significant leaks.
The Role of the LDP Switch Circuit
The “switch circuit” referenced in code P1479 is the electrical feedback path from the LDP to the PCM. The switch inside the LDP changes state (open/closed) as the pump diaphragm moves. The PCM expects to see this specific change in voltage or resistance on the signal wire when it commands the pump on. Code P1479 is set when the PCM does not see the expected electrical response from the LDP switch during the self-test, signaling a circuit problem.
Common Symptoms and Causes of P1479
A vehicle with a stored P1479 code may exhibit a range of symptoms, or in some cases, no noticeable drivability issues at all. However, a malfunctioning EVAP system can affect fuel efficiency and will cause the vehicle to fail an emissions inspection.
Symptoms of a P1479 Fault
- Illuminated Check Engine Light (MIL): This is the most common and often the only symptom.
- Failed Emissions Test: The vehicle will not pass a state or local emissions inspection due to an active EVAP system fault.
- Possible Fuel Odor: While less common with this specific circuit code, a compromised EVAP system can sometimes lead to a smell of gasoline.
- Other EVAP Codes: P1479 may appear alongside other EVAP codes like P0442 (small leak) or P0455 (large leak) if the faulty LDP prevents a proper test.
Primary Causes of Code P1479
- Faulty Leak Detection Pump (LDP): The internal switch mechanism has failed. This is a very common cause.
- Open or Shorted Wiring: Damaged, corroded, or broken wires in the harness connecting the LDP to the PCM.
- Poor Electrical Connections: Corrosion or looseness at the LDP electrical connector or PCM connector.
- Blown Fuse: A fuse supplying power to the LDP or the PCM circuit may be blown.
- Faulty Powertrain Control Module (PCM): This is rare, but a malfunction within the PCM itself cannot be completely ruled out after all other causes are eliminated.
Step-by-Step Diagnostic and Repair Guide for P1479
Diagnosing P1479 requires a systematic approach, starting with the simplest checks. A professional-grade OBD2 scanner and a digital multimeter (DMM) are essential tools for this job.
Step 1: Preliminary Inspection and Code Verification
Begin by performing a thorough visual inspection. Look for obvious damage to the Leak Detection Pump, which is typically located near the fuel tank or in the rear wheel well. Check the wiring harness for chafing, cuts, or burn marks. Inspect the electrical connector for corrosion, bent pins, or looseness. Clear the code with your scanner, perform a drive cycle, and see if P1479 returns. If it returns immediately, it indicates a hard fault.
Step 2: Electrical Circuit Testing
Consult a vehicle-specific wiring diagram to identify the pinouts for the LDP connector. Typically, you will find pins for power, ground, and the switch signal. Using your multimeter:
- Check for battery voltage at the power supply wire with the ignition ON.
- Check the ground circuit for continuity to a known good ground.
- Test the switch signal wire for continuity to the PCM and check for shorts to power or ground.
Any deviation from specifications indicates a wiring or connector issue that must be repaired.
Step 3: Testing the Leak Detection Pump Itself
If the wiring checks out, the LDP itself is likely faulty. You can perform a bench test. Apply battery voltage and ground to the pump motor terminals; you should hear and feel it run. The internal switch can be tested for continuity/resistance change across its terminals while manually operating the pump diaphragm (if accessible). A pump that doesn’t run or shows no change in switch state is defective.
Step 4: Repair and Clear Codes
Based on your findings:
- Repair Wiring: Solder and seal any damaged wires. Replace corroded connectors.
- Replace the LDP: This is the most common fix. Ensure the replacement part is correct for your specific model year.
- Address Other Issues: Replace any blown fuses.
After repair, clear all codes with your scanner. The PCM will need to complete a full EVAP monitor drive cycle to confirm the fix. A successful test will result in the “EVAP Monitor” showing as “Ready” or “Complete” on your scanner, with no return of the P1479 code.
Importance of Addressing P1479 for Vehicle Health
While a P1479 code may not strand you on the side of the road, it signifies a failure in a critical emissions control system. Ignoring it has consequences beyond just an annoying warning light.
Emissions Compliance and Environmental Impact
The EVAP system is mandated by law to reduce hydrocarbon emissions. A faulty system allows unburned fuel vapors to escape, contributing to air pollution and smog. Your vehicle will be unable to pass mandatory emissions testing, which can lead to registration suspension in many regions.
Preventing Secondary Issues
A malfunctioning Leak Detection Pump can prevent the PCM from accurately testing the rest of the EVAP system. This means a potentially serious fuel vapor leak from a cracked hose or faulty gas cap could go undetected, posing a minor safety risk and negatively impacting fuel economy over time. Diagnosing and repairing P1479 restores the vehicle’s full self-diagnostic capability for the entire EVAP system.