Understanding the GMC P146E Diagnostic Trouble Code
The OBD2 code P146E is a manufacturer-specific diagnostic trouble code (DTC) for General Motors (GM) vehicles, including GMC trucks and SUVs. It is defined as **”Evaporative Emission System Leak Detection Pump Control Circuit High.”** This code indicates a fault within the electrical control circuit for the Leak Detection Pump (LDP), a critical component of the vehicle’s Evaporative Emission Control (EVAP) system. The Powertrain Control Module (PCM) has detected a voltage signal on the LDP control circuit that is higher than expected when the pump is commanded off, signaling a potential short to power or an internal pump failure. A persistent P146E will illuminate the Check Engine Light and can prevent the vehicle from completing crucial EVAP system self-tests.
The Role of the EVAP System and 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 is the system’s “lungs.” It pressurizes the sealed fuel system with air to check for leaks. The PCM controls the LDP by sending a Pulse Width Modulated (PWM) signal on a specific control wire. A “circuit high” fault means the PCM sees voltage on this control line when it should be at or near zero volts, indicating an electrical problem.
Common Symptoms and Causes of P146E in GMC Vehicles
While the EVAP system is primarily an emissions control system, a P146E code can sometimes have subtle or noticeable effects. The most common symptom is an illuminated Malfunction Indicator Lamp (MIL), or Check Engine Light. In some cases, you may notice a slight fuel odor, but often there are no direct drivability issues like stalling or poor performance. However, because the PCM cannot run EVAP monitor tests, the vehicle may fail an emissions inspection.
Primary Causes of a P146E Code
- Shorted Leak Detection Pump Control Circuit: The most frequent cause. The wire controlling the LDP may be shorted to a 12-volt power source (e.g., chafing against a sharp edge or a damaged harness).
- Failed Leak Detection Pump (Internal Short): The LDP itself can fail internally, causing a short circuit that sends voltage back to the PCM.
- Faulty Powertrain Control Module (PCM): Although less common, a malfunction within the PCM’s driver circuit for the LDP can trigger this code. This should be diagnosed only after all wiring and component checks.
- Damaged or Corroded Wiring/Connectors: Corrosion at the LDP connector, PCM connector, or anywhere along the control circuit can create a high-resistance short or faulty signal.
Vehicles Commonly Affected by P146E
This code is prevalent in many GM platforms. Common GMC models include:
- GMC Sierra (1500, 2500, 3500)
- GMC Yukon / Yukon XL
- GMC Canyon
- GMC Acadia
- GMC Terrain
The diagnostic approach is similar across these models, though the physical location of the LDP may vary (often found near the fuel tank or in the engine bay).
Step-by-Step Diagnostic and Repair Procedure for P146E
Diagnosing a P146E requires a systematic approach, starting with the simplest checks and moving toward more complex ones. You will need a quality digital multimeter (DMM) and a reliable OBD2 scanner capable of reading live data and performing actuator tests.
Step 1: Preliminary Inspection and Code Verification
Begin by recording all stored and pending codes. Clear the code and perform a test drive to see if it returns immediately (indicating a hard fault) or after a few drive cycles. Visually inspect the Leak Detection Pump, its electrical connector, and the associated wiring harness for obvious damage, corrosion, or disconnection. Look for signs of rodent damage or wires rubbing against the chassis.
Step 2: Electrical Circuit Testing
This is the core of the diagnosis. With the vehicle’s ignition OFF, disconnect the electrical connector from the Leak Detection Pump.
- Check for Short to Power: Set your multimeter to DC Volts. Probe the LDP control circuit pin in the vehicle harness connector (refer to a service manual for the exact pin). With the ignition ON (engine OFF), there should be less than 1 volt. If you read full battery voltage (approx. 12V), the control circuit is shorted to power somewhere between the PCM and the connector.
- Check Circuit Integrity: Use the multimeter’s resistance (ohms) function to check for continuity between the LDP control circuit pin at the harness and the corresponding pin at the PCM connector. Also, check for a short to ground on the same control wire.
Step 3: Component Testing (Leak Detection Pump)
If the wiring checks out, the pump itself is likely faulty. You can perform a bench test:
- Using the multimeter in ohms mode, measure the resistance between the two terminals of the LDP motor. You should typically get a low resistance reading (a few ohms). An open circuit (infinite resistance) or a direct short (0 ohms) indicates a failed pump.
- Some advanced scanners can command the LDP ON and OFF. Listen for a clicking or humming sound from the pump. No sound, combined with a confirmed good signal from the PCM, points to a dead pump.
Replacing the LDP is often the solution if the wiring is intact and voltage is present at the connector when it shouldn’t be.
Step 4: Final Verification and Clearance
After repairing the fault—whether it’s repairing a damaged wire, cleaning a corroded connector, or replacing the LDP—clear the P146E code with your scanner. Perform a complete drive cycle to allow the PCM to run all its monitors, including the EVAP leak test. Verify that the Check Engine Light remains off and that the code does not return as a pending or confirmed fault.
Professional Tips and Important Considerations
Diagnosing electrical codes like P146E can be challenging. Always consult the specific vehicle’s wiring diagram for pinouts and wire colors. Intermittent faults may require wiggling the harness while monitoring live data or using a graphing multimeter to catch a fleeting voltage spike. Remember, never replace the PCM without absolute confirmation from thorough electrical testing, as it is the most expensive and least likely component to fail in this scenario.
Preventative Maintenance and Related Codes
To avoid EVAP system issues, ensure your gas cap is tightened securely after refueling. Codes related to P146E that may appear simultaneously or separately include:
- P0496: Evaporative Emission System High Purge Flow – Often related to purge valve issues.
- P0442 / P0455: Small/Large EVAP System Leak – The LDP’s primary job is to find these leaks.
- P146D: Leak Detection Pump Sense Circuit – A different electrical fault in the LDP’s feedback circuit.
Addressing a P146E promptly ensures your GMC remains emissions-compliant and prevents minor electrical issues from escalating into more significant problems.