Understanding OBD2 Code P1473 in Mercury Vehicles
OBD2 diagnostic trouble code (DTC) P1473 is a manufacturer-specific code primarily associated with Ford Motor Company vehicles, including the Mercury brand. This code indicates a fault within the Evaporative Emission Control (EVAP) system, specifically related to the Leak Detection Pump (LDP) or its control circuit. The EVAP system is crucial for preventing fuel vapors from escaping into the atmosphere by capturing and storing them in the charcoal canister before purging them into the engine to be burned. Code P1473 is defined as “EVAP Leak Detection Pump Switch or Mechanical Fault”. When this code is set, the vehicle’s Powertrain Control Module (PCM) has detected an irregularity in the operation or feedback signal from the LDP, which is responsible for pressurizing the EVAP system to check for leaks.
Role of the Leak Detection Pump (LDP) in the EVAP System
The Leak Detection Pump is a critical component for modern onboard EVAP system monitoring (often referred to as the “EVAP monitor” or “leak test”). Unlike traditional systems that used engine vacuum, the LDP is an electrically operated pump that creates a controlled vacuum or pressure within the fuel tank and EVAP lines. During a diagnostic cycle (typically after a cold start under specific driving conditions), the PCM activates the LDP. It then monitors the pump’s operation and the pressure/vacuum signature to determine if the system is sealed. A mechanical failure, electrical fault, or a significant leak will cause the test to fail, triggering code P1473.
Common Symptoms and Causes of P1473
While P1473 may not always cause immediate drivability issues, it is a persistent fault that will illuminate the Check Engine Light (CEL) and cause the vehicle to fail an emissions inspection. Ignoring it can lead to increased hydrocarbon emissions and, in some cases, related performance problems.
Primary Symptoms of Code P1473
- Illuminated Check Engine Light (MIL): The most common and often the only initial symptom.
- Failed Emissions Test: The vehicle will not pass state or local emissions inspections with an active EVAP code.
- Possible Fuel Odor: If the fault is related to a physical leak or a stuck-open LDP valve, a smell of gasoline may be noticeable, especially near the fuel tank or under the hood.
- Other EVAP Codes: P1473 may be stored alongside other codes like P0442 (small leak) or P0455 (large leak) if the LDP failure prevents proper leak testing.
Root Causes of P1473 Mercury Code
The causes for P1473 can be categorized into electrical, mechanical, and systemic issues. A methodical diagnosis is required to pinpoint the exact fault.
- Faulty Leak Detection Pump (LDP): The most common cause. The pump’s internal motor can fail, its diaphragm can rupture, or internal valves can stick open or closed.
- Electrical Issues in the LDP Circuit: This includes damaged wiring, corroded connectors, poor grounds, or a blown fuse supplying power to the LDP.
- Failed LDP Pressure Switch/Sensor: Many LDP units contain an internal pressure switch that provides feedback to the PCM. A failed switch will cause this code.
- Blocked or Pinched EVAP Hoses: Hoses leading to or from the LDP, charcoal canister, or fuel tank can become kinked, clogged, or disconnected.
- Faulty Charcoal Canister: A saturated or damaged canister can restrict flow and affect LDP operation.
- Defective PCM (Rare): While uncommon, a malfunctioning PCM that cannot properly control the LDP circuit can be the source.
Step-by-Step Diagnostic and Repair Procedure
Diagnosing P1473 requires a systematic approach, starting with the simplest checks and progressing to component testing. You will need a quality OBD2 scanner, a digital multimeter (DMM), and a hand vacuum pump/gauge.
Step 1: Preliminary Inspection and Code Verification
Begin with a thorough visual inspection. Check for obvious damage to the EVAP system components, which are often located near the fuel tank or in the engine bay. Look for cracked, brittle, or disconnected hoses. Inspect the wiring harness and connector at the LDP (usually mounted near the fuel tank or rear axle) for corrosion, bent pins, or chafing. Clear the code with your scanner and perform a drive cycle to see if it returns immediately or only after the EVAP monitor runs. An immediate return suggests a hard electrical fault.
Step 2: Electrical Circuit Testing
Consult a vehicle-specific wiring diagram. With the key in the ON position (engine off), use your DMM to check for battery voltage at the LDP power supply wire. Check for continuity on the ground circuit. Next, back-probe the signal/control wire from the PCM. You may need a scanner with bidirectional controls to command the LDP on and off while monitoring the voltage change on this wire, or use the multimeter to see if a control signal is present during an active test.
Step 3: Testing the Leak Detection Pump Itself
If the electrical circuit is sound, the LDP itself is suspect. Disconnect the EVAP hoses from the pump. You can perform a functional test by applying battery voltage and ground directly to the pump terminals (briefly); you should hear and feel it click or operate. A hand vacuum pump can be used on certain ports of the LDP to check for internal diaphragm integrity and valve operation (refer to a service manual for specific testing procedures for your model, as LDP designs vary). Often, if electrical power is confirmed and the pump does not respond, it is faulty.
Step 4: Checking for Systemic Blockages and Leaks
Before replacing the LDP, ensure the rest of the system is clear. Use your hand vacuum pump to apply a slight vacuum to the EVAP line that runs to the engine. It should hold vacuum. Check for blockages by attempting to blow air through hoses (disconnected from components). Inspect the gas cap for a damaged or missing seal, as this is a common source of leaks that can interfere with the LDP test.
Step 5: Clearing the Code and Performing a Monitor Test
After repairs (e.g., replacing the LDP, repairing a wire, clearing a blocked hose), clear the DTCs with your scanner. To confirm the repair, the vehicle’s EVAP monitor must complete a full diagnostic cycle. This usually requires a specific drive cycle (often a mix of city and highway driving over 30-50 minutes). Use your scanner to check the “monitor status” to confirm the EVAP system shows “Ready” or “Complete,” indicating the test passed with no codes reset.
Vehicle-Specific Notes and Conclusion
Code P1473 is commonly found on Mercury vehicles that share platforms with Ford models, such as the Mercury Grand Marquis, Mountaineer, Sable, and Monterey. The diagnostic process is largely consistent across these models, though the physical location of the LDP may vary. Always prioritize a thorough visual and electrical inspection before condemning the pump, as wiring issues are frequent, especially in areas prone to corrosion.
Importance of Timely Repair
Addressing a P1473 code is essential not only for emissions compliance but also for ensuring the overall integrity of your vehicle’s fuel system. A malfunctioning LDP can mask larger EVAP leaks, potentially leading to fuel vapor loss, a noticeable gasoline odor, and in extreme cases, could affect engine performance during purge events. While the repair might involve a moderate level of DIY skill, particularly for electrical testing, a precise diagnosis will save time and money over simply throwing parts at the problem.