What is OBD2 Code P146D on a Buick?
OBD2 diagnostic trouble code (DTC) P146D is a manufacturer-specific code primarily associated with General Motors (GM) vehicles, including various Buick models. The official definition is “Fuel Tank Pressure Sensor Circuit Low Voltage.” This code is part of the vehicle’s sophisticated Evaporative Emission Control (EVAP) system, which is designed to prevent fuel vapors from escaping into the atmosphere. When the powertrain control module (PCM) detects that the voltage signal from the fuel tank pressure (FTP) sensor is consistently lower than the expected range for a specified period, it logs code P146D and illuminates the check engine light (CEL).
The Role of the Fuel Tank Pressure Sensor
The FTP sensor is a critical component located on or near the fuel tank. Its primary function is to monitor pressure and vacuum levels within the sealed fuel system. This data is essential for the PCM to:
- Detect leaks in the EVAP system (a key part of emissions compliance).
- Control the purge valve to allow stored fuel vapors to be drawn into the engine and burned.
- Monitor the integrity of the fuel tank and its related components during self-tests.
A “circuit low voltage” reading indicates the signal wire is reporting a voltage near zero volts, suggesting a short to ground, an open circuit, or a faulty sensor.
Common Symptoms of Buick P146D Code
Unlike some engine codes that cause drivability issues, P146D is primarily an emissions-related fault. Drivers may notice subtle signs or none at all. However, the following symptoms are commonly associated with this code:
- Illuminated Check Engine Light (MIL): This is the most universal and often the only symptom.
- Failed Emissions Test: The vehicle will not pass a state or local emissions inspection with an active EVAP system code.
- Slight Fuel Odor: In some cases, a small leak in the EVAP system may allow fuel vapors to escape, which might be noticeable near the fuel tank or filler neck.
- Reduced Fuel Efficiency: While not always pronounced, a malfunctioning EVAP system can sometimes lead to a minor decrease in miles per gallon (MPG).
- No Observable Symptoms: Often, the car will drive completely normally, with the check engine light being the sole indicator of a problem.
Buick Models Commonly Affected
Code P146D has been documented in various Buick models that share GM’s global vehicle platforms and EVAP system architecture. Common models include:
- Buick Enclave
- Buick LaCrosse
- Buick Regal
- Buick Encore
- Buick Verano
Diagnosing the Cause of P146D: A Step-by-Step Guide
Accurate diagnosis is key to an effective repair. A systematic approach using a professional-grade OBD2 scanner and a digital multimeter (DMM) is required. Warning: Always ensure the work area is well-ventilated and follow safety procedures when working around the fuel system.
Step 1: Preliminary Checks and Code Verification
Begin by using your scan tool to confirm the presence of P146D. Clear the code and perform a test drive to see if it returns immediately or only under certain conditions (like a specific fuel level). Check the vehicle’s service bulletins (TSBs) for any known issues related to the FTP sensor on your specific Buick model and year.
Step 2: Visual Inspection of Wiring and Connectors
Carefully inspect the wiring harness connected to the FTP sensor, typically located on top of the fuel tank or along the fuel filler neck. Look for:
- Chafed, pinched, or burnt wires.
- Corroded or loose electrical connectors.
- Physical damage to the sensor itself.
Address any obvious physical damage before proceeding to electrical tests.
Step 3: Electrical Testing of the FTP Sensor Circuit
With the ignition OFF, disconnect the electrical connector from the FTP sensor. Using a wiring diagram for your specific vehicle is highly recommended. Key tests include:
- Reference Voltage (5V): With the ignition ON, probe the reference voltage wire (often 5V). A reading significantly lower than 5V indicates a problem in the supply circuit from the PCM.
- Signal Circuit: Check the signal wire for a short to ground. With the connector still disconnected, measure resistance between the signal pin and chassis ground. It should be open (infinite resistance). A low resistance confirms a short.
- Ground Circuit: Check the ground wire for continuity to a good chassis ground. A high resistance indicates a bad ground connection.
Step 4: Testing the Fuel Tank Pressure Sensor Itself
If the wiring checks out, the sensor itself is likely faulty. You can perform a basic bench test. Using the DMM in resistance or voltage mode, apply a gentle vacuum (with a hand pump) to the sensor’s reference port while monitoring the signal output. The resistance or voltage should change smoothly. A dead, sticky, or erratic sensor needs replacement.
Repair Solutions for Buick P146D Code
Once the root cause is identified, the repair is typically straightforward. The most common fixes are listed below.
Repair 1: Fixing Damaged Wiring or Connectors
If the inspection reveals damaged wiring, repair it by splicing in new wire using solder and heat-shrink tubing—never use twist-on connectors in automotive environments. Clean any corroded connector terminals with electrical contact cleaner.
Repair 2: Replacing the Faulty Fuel Tank Pressure Sensor
This is the most common repair for a confirmed P146D. The FTP sensor is usually held in place by a locking ring or bolts. Important: The fuel tank pressure must be equalized to atmospheric pressure before removal. This often involves loosening the gas cap and waiting. Follow the specific service procedure for your Buick to safely depressurize the system and replace the sensor.
Repair 3: Addressing PCM Issues (Rare)
In very rare instances, a faulty PCM that fails to supply the proper 5-volt reference could be the cause. This should only be considered after all wiring and the sensor itself have been definitively ruled out. Professional reprogramming or replacement may be necessary.
Post-Repair Procedure and Code Clearing
After completing the repair, clear the P146D code with your scan tool. The PCM will need to run a complete EVAP system monitor test to verify the fix. This drive cycle is often specific and may require a mix of highway and city driving over several trips. Use your scanner to check the “monitor status” to confirm all emissions tests, especially the EVAP test, have been completed successfully. Once the monitor runs and passes, the check engine light should remain off, indicating a successful repair.