Understanding the P1479 OBD2 Code in Chevrolet Vehicles
The OBD2 diagnostic trouble code P1479 is a manufacturer-specific code primarily associated with General Motors (GM) vehicles, including Chevrolet models like the Silverado, Tahoe, Suburban, and many others. This code directly points to an electrical fault within the Evaporative Emission Control (EVAP) system, specifically the circuit controlling the Leak Detection Pump (LDP) or, in some models, the Evaporative Emission (EVAP) Canister Vent Solenoid. The EVAP system is crucial for capturing fuel vapors from the fuel tank and preventing them from escaping into the atmosphere. A P1479 code indicates that the vehicle’s Powertrain Control Module (PCM) has detected an irregularity—such as an open, short to ground, or short to power—in the electrical control circuit for this component.
Common Symptoms and Causes of P1479
When the PCM logs a P1479 code, it will also illuminate the Check Engine Light (CEL) on your dashboard. Unlike some drivability codes, P1479 may not cause immediate, noticeable performance issues, but it signifies a failure in the emission control system that needs attention.
Primary Symptoms of Code P1479
- Illuminated Check Engine Light (MIL): The most consistent and immediate symptom.
- Failed Emissions Test: The vehicle will not pass a state or local emissions inspection.
- Possible Fuel Odor: In some cases, a faint smell of gasoline may be detected if the EVAP system is not sealing properly.
- No Drivability Issues: The engine typically runs normally, with no loss of power or rough idle directly attributable to this code.
Root Causes of a P1479 Diagnostic Trouble Code
- Faulty Leak Detection Pump (LDP) or Vent Solenoid: The internal coil of the pump or solenoid can fail open or shorted.
- Damaged Wiring or Connectors: Corroded, broken, or frayed wires in the control circuit between the PCM and the LDP.
- Poor Electrical Connections: A loose or corroded connector at the LDP or the PCM.
- Blown Fuse: A fuse supplying power to the EVAP system components may be blown.
- Faulty Powertrain Control Module (PCM): While rare, a malfunction within the PCM itself can cause this code.
Step-by-Step Diagnostic Procedure for P1479
Diagnosing a P1479 code requires a systematic approach, a digital multimeter (DMM), and a reliable OBD2 scanner. Always begin by verifying the code and checking for technical service bulletins (TSBs) for your specific Chevrolet model and year.
Step 1: Preliminary Inspection and Code Verification
Use your OBD2 scanner to confirm the presence of P1479. Clear the code and perform a test drive to see if it returns. This confirms an active fault. Simultaneously, perform a thorough visual inspection of the EVAP system. Locate the Leak Detection Pump (typically near the fuel tank or canister). Check for obvious damage, disconnected hoses, and inspect the wiring harness and electrical connector for corrosion, bent pins, or physical damage.
Step 2: Electrical Circuit Testing
With the vehicle’s ignition OFF, disconnect the electrical connector from the LDP. Using a wiring diagram for your specific model is highly recommended. Set your multimeter to measure resistance (Ohms). Test the resistance across the two terminals of the LDP solenoid. You should typically get a reading between 10 and 30 ohms. A reading of infinite resistance (OL) indicates an open coil, and a reading near zero indicates a shorted coil—both require pump replacement.
Step 3: Power and Ground Circuit Check
Reconnect the connector to the LDP. Back-probe the wires with your multimeter probes (use care to avoid damage). With the ignition ON (engine OFF), one wire should show battery voltage (approx. 12V). This is the power feed, often controlled by a fuse. The other wire is the control wire from the PCM. Using a scan tool with bidirectional controls, command the LDP ON and OFF. You should see the voltage on the control wire change accordingly (e.g., from 12V to near 0V when commanded ON). If there is no change, the issue is in the control circuit or PCM.
Step 4: Continuity and Short Testing
With the ignition OFF and the LDP connector disconnected, test for continuity between the PCM control pin and the corresponding pin at the LDP connector. There should be continuity (low resistance). Also, check for a short to ground or power on this control wire by testing between the control wire and chassis ground (should be no continuity) and between the control wire and the battery positive wire (should be no continuity when disconnected).
Repair Solutions and Prevention
Once the faulty component is identified, the repair is generally straightforward. The complexity often lies in accessing the component, which may require raising the vehicle.
Common Repair Procedures
- Replacing the Leak Detection Pump/Vent Solenoid: This is the most common fix. Ensure you get the correct OEM or high-quality aftermarket part for your specific model. After replacement, clear codes and perform an EVAP system monitor drive cycle to confirm repair.
- Repairing Wiring Harness: For damaged wires, solder and seal the connection properly. Use heat-shrink tubing for a professional, weatherproof repair. Never use twist-on connectors in automotive environments.
- Cleaning Connectors:
Use electrical contact cleaner and a small brush to remove corrosion from connector pins. Apply a dielectric grease to prevent future corrosion.
- Replacing Fuses: If a fuse is blown, replace it with one of the identical amperage rating. Investigate why it blew to prevent recurrence.
Preventive Maintenance Tips
While electrical failures can be unpredictable, you can minimize risks. Periodically inspect underbody components for damage, especially if you drive on rough roads. Keep the EVAP system components and their connectors clean from road grime and salt. Address any other EVAP-related codes (like small or large leak codes) promptly, as system pressure issues can sometimes stress electrical components.
Conclusion: Is P1479 a Serious Code?
Code P1479 is not typically an emergency that will strand you on the side of the road, as it does not directly affect engine combustion. However, it is a serious emissions-related fault. Ignoring it will cause your Chevrolet to fail its next emissions test and keeps the Check Engine Light on, which can prevent you from noticing other, more critical codes. Furthermore, a malfunctioning EVAP system can allow fuel vapors to escape, which is harmful to the environment and can, in rare cases, lead to a gasoline odor. Following the structured diagnostic approach outlined above will allow you or your technician to accurately pinpoint and resolve the electrical fault in the EVAP leak detection pump control circuit, restoring your vehicle’s emission system to proper function.