Understanding and Fixing OBD2 Code P1499 on Chrysler Vehicles

Decoding the P1499 Chrysler Fault Code

When your Chrysler, Dodge, or Jeep’s check engine light illuminates and an OBD2 scanner retrieves code P1499, you are dealing with a specific fault within the vehicle’s Evaporative Emission Control (EVAP) system. Formally defined as “Leak Detection Pump Switch or Mechanical Fault,” this diagnostic trouble code (DTC) is common in many Chrysler Group vehicles from the late 1990s through the 2000s. The EVAP system is crucial for preventing fuel vapors from escaping into the atmosphere, and the Leak Detection Pump (LDP) is its self-diagnostic heart. A P1499 code indicates the Powertrain Control Module (PCM) has detected an irregularity in the LDP’s operation, either in its internal vacuum switch or its mechanical ability to pump air.

Core Function of the Leak Detection Pump (LDP)

Unlike a simple fuel vapor canister purge valve, the LDP is an active diagnostic component. Its primary jobs are:

• System Pressurization: The LDP uses engine vacuum and a solenoid to pump air into the sealed EVAP system (fuel tank and lines).
• Leak Monitoring: It contains a pressure switch that tells the PCM when a target pressure is reached.
• Fault Detection: By timing how long it takes to pressurize the system or how well it holds pressure, the PCM can infer if there is a large leak, a small leak, or a fault in the LDP itself.

Code P1499 is set when the PCM’s expected electrical signal from the LDP’s internal switch does not match the actual mechanical state of the pump during a test cycle.

Symptoms and Common Causes of P1499

While sometimes the P1499 code may set with no noticeable drivability issues, it often presents with specific symptoms. Ignoring it can lead to a failed emissions test and potentially mask other EVAP leaks.

Primary Symptoms of a P1499 Fault

• Illuminated Check Engine Light (MIL): The most common and often the only initial symptom.
• Failed Emissions Inspection: The vehicle will not pass a state-mandated OBD2 emissions test with an active EVAP code.
• Possible Fuel Odor: If the LDP is stuck open or the EVAP system is compromised, you may smell gasoline vapors, especially near the fuel tank or after refueling.
• Other EVAP Codes: P1499 may appear alongside codes like P0442 (small leak) or P0455 (large leak) if the faulty LDP is preventing accurate leak detection.

Root Causes of Chrysler P1499 Code

Diagnosis should follow a logical path from simplest to most complex. The main culprits are:

• Faulty Leak Detection Pump (LDP): The most common cause. The internal diaphragm can tear, the solenoid can fail, or the pressure switch can become inoperative.
• Blocked, Pinched, or Cracked EVAP Hoses: Vacuum lines to and from the LDP or the main EVAP canister hose can collapse, leak, or become clogged with debris.
• Electrical Issues: Corroded connectors, damaged wiring, or poor electrical grounds at the LDP connector or PCM can cause erroneous signals.
• Faulty PCM: Rare, but a possibility if all other components and wiring check out perfectly. This is a diagnosis of last resort.

Step-by-Step Diagnostic and Repair Procedure

A methodical approach is key to correctly fixing P1499. You will need a quality OBD2 scanner capable of viewing live data and, ideally, activating components (bi-directional control). A digital multimeter (DMM) and a hand-held vacuum pump/gauge are also essential tools.

Step 1: Preliminary Inspection and Visual Check

Begin with the basics. Locate the Leak Detection Pump (typically found near the fuel tank or in the rear wheel well). Carefully inspect:

• All EVAP hoses for cracks, dryness, rot, or disconnections.
• The LDP electrical connector for corrosion, bent pins, or moisture.
• The integrity of the vacuum lines connected to the LDP and the check valve.
• The physical condition of the LDP itself for damage.

Step 2: Functional Testing of the Leak Detection Pump

Use your bi-directional scanner to command the LDP solenoid “ON” and “OFF.” You should hear a distinct click from the pump with each command. If no click is heard, test further:

• Circuit Test: With the connector disconnected, use the DMM to check for battery voltage (typically 12V) on the power wire with the ignition ON. Check the ground circuit for continuity.
• Solenoid Test: Measure the resistance of the LDP solenoid across its two pins. Compare to manufacturer specifications (often between 10-30 ohms). An open (infinite) or short (0 ohms) reading indicates a bad LDP.
• Mechanical/Vacuum Test: Disconnect the vacuum hoses. Using a hand vacuum pump, apply vacuum to the pump’s diaphragm port. It should hold vacuum steadily. A leak indicates a torn diaphragm.

Step 3: Checking the LDP Switch Signal

This tests the internal pressure switch. With the scanner viewing live data, look for the “LDP Switch” or “Leak Pump Sense” parameter. It typically reads OPEN or CLOSED. While manually applying vacuum to the LDP diaphragm port (simulating a pump stroke), the switch state in the scanner should change. If it doesn’t, the internal switch is faulty, confirming the need for LDP replacement.

Step 4: Replacement and Final Verification

Once a faulty LDP is confirmed, replacement is straightforward:

• Disconnect the negative battery cable.
• Disconnect the electrical connector and vacuum hoses, noting their positions.
• Remove the mounting bolts and the old LDP.
• Install the new unit, reconnect all hoses and the electrical connector.
• Reconnect the battery.

Clear the P1499 code with your scanner. The monitor will need to complete a full drive cycle. Perform a final scan to confirm the code does not return and that the EVAP monitor runs and completes successfully.

Conclusion: Ensuring a Lasting Repair

Code P1499 on Chrysler vehicles is a direct communication from the PCM that the self-check capability of the EVAP system is compromised. While the Leak Detection Pump itself is the frequent failure point, a thorough diagnosis that includes inspecting related vacuum lines and electrical circuits is critical to avoid comebacks. By following the structured diagnostic steps outlined above, you can accurately identify the root cause—whether a mechanical pump failure, a blocked hose, or an electrical fault—and restore the vehicle’s emission control system to proper working order. Addressing P1499 promptly not only extinguishes the check engine light but also ensures your vehicle operates efficiently and remains environmentally compliant.