Understanding the P1490 Chrysler Diagnostic Trouble Code
The OBD2 diagnostic trouble code P1490 is a manufacturer-specific code primarily associated with Chrysler, Dodge, Jeep, and Ram vehicles. This code indicates a fault within the Leak Detection Pump (LDP) circuit. The Leak Detection Pump is a critical component of the vehicle’s Evaporative Emission Control (EVAP) system. Its primary function is to pressurize the fuel tank and fuel vapor lines to check for leaks that could allow harmful hydrocarbons to escape into the atmosphere. When the Powertrain Control Module (PCM) detects an electrical fault—such as an open, short, or performance issue—in the LDP’s control circuit, it will log code P1490 and illuminate the check engine light.
Role of the EVAP System and Leak Detection Pump
The EVAP system is designed to capture and store fuel vapors from the fuel tank, preventing them from being released into the environment. The Leak Detection Pump is the system’s self-diagnostic tool. During specific drive cycles, the PCM activates the LDP. The pump draws in clean air from the atmosphere, uses it to pressurize the EVAP system, and then monitors the pressure decay. If the pressure drops too quickly, it indicates a leak, triggering a different code (like a P0442 small leak). Code P1490, however, signifies that the computer cannot properly command or monitor the LDP itself due to an electrical problem.
Common Symptoms and Causes of Code P1490
Unlike codes that cause drivability issues, P1490 is often a “silent” code with no direct impact on engine performance or fuel economy. However, it is a critical failure that prevents the vehicle from completing its EVAP self-check, which can lead to a failed emissions test.
Primary Symptoms of a P1490 Fault
- Illuminated Check Engine Light (MIL): The most common and often only noticeable symptom.
- Failed Emissions Inspection: The vehicle will not pass a state emissions test due to an incomplete EVAP monitor.
- Other EVAP Codes: P1490 may be stored alongside other EVAP-related codes like P0442 or P0455.
- Possible Fuel Odor: In rare cases if combined with a physical leak, a gasoline smell may be present.
Root Causes of Chrysler P1490 Code
- Faulty Leak Detection Pump (LDP): The internal motor or solenoid within the pump has failed.
- Open or Shorted Wiring: Damaged, corroded, or broken wires in the LDP control circuit between the PCM and the pump.
- Bad LDP Relay: Many Chrysler vehicles use a dedicated relay to power the Leak Detection Pump. A failed relay is a very common cause.
- Poor Electrical Connections: Corrosion or looseness at the LDP connector or PCM connector.
- Defective Powertrain Control Module (PCM): Although less common, a failed driver circuit within the PCM itself can cause this code.
Step-by-Step Diagnostic Procedure for P1490
A systematic approach is essential to correctly diagnose a P1490 code. You will need a quality digital multimeter (DMM) and a wiring diagram for your specific vehicle.
Step 1: Preliminary Checks and Visual Inspection
Begin with a thorough visual inspection. Locate the Leak Detection Pump (typically found in the rear of the vehicle near the fuel tank or behind a rear wheel well liner). Check the wiring harness and connector for obvious damage, chafing, or corrosion. Inspect the LDP relay, often found in the Power Distribution Center (PDC) under the hood. Consult your owner’s manual for its location. Swap the LDP relay with an identical, known-good relay (like the horn or fog light relay) to see if the code clears.
Step 2: Electrical Testing of the Leak Detection Pump
Disconnect the electrical connector from the LDP. With the key in the ON position (engine off), use your multimeter to check for power and ground at the connector.
- Power Circuit: One pin should show battery voltage (typically 12V). This is supplied through the LDP relay.
- Control Circuit: The other pin is the control circuit from the PCM. With the key on, it may show a reference voltage (often 5V or 12V). When the PCM activates the pump, it grounds this circuit.
- Pump Resistance: Measure the resistance across the two terminals of the LDP motor itself. A reading of infinity (open) or zero (short) indicates a failed pump. A typical good LDP will show a specific resistance, often between 10-30 ohms (consult service data).
Step 3: Circuit Integrity and PCM Verification
If power and ground are present but the pump doesn’t run when commanded (using a bidirectional scan tool), the pump is likely faulty. If power is missing, trace the circuit back to the relay and fuse. If the control signal from the PCM is missing, check for continuity in the wire from the LDP connector back to the PCM connector. Also check for a short to power or ground in this control wire. If all wiring checks out, the issue may be a faulty driver inside the PCM.
Repair Solutions and Professional Recommendations
Once the faulty component is identified, the repair is typically straightforward. Always clear the code after repairs and perform a drive cycle to ensure the EVAP monitor runs and the code does not return.
Common Repair Procedures
- Replacing the LDP Relay: The simplest and most cost-effective fix if the relay is the culprit. Use an OEM or high-quality equivalent part.
- Replacing the Leak Detection Pump: Requires removing the old pump, transferring any necessary fittings or hoses, and installing the new unit. Ensure the connector is clean and secure.
- Repairing Wiring Harness: Solder and seal any repaired wires. Use heat-shrink tubing for a professional, durable repair. Never use twist-on connectors in automotive environments.
- PCM Replacement/Reprogramming: This is a last-resort option. A specialist should verify the PCM is defective. Replacement units often require VIN-specific programming.
Why You Should Not Ignore Code P1490
While your vehicle may run fine, ignoring a P1490 code has consequences. Primarily, it will cause your vehicle to fail any OBD2-based emissions test, as the EVAP monitor will remain in an “incomplete” state. Furthermore, it means a part of your vehicle’s emissions system is non-functional, allowing for potential, undetected fuel vapor leaks. Diagnosing and repairing P1490 restores the integrity of your EVAP system, ensures compliance with emissions regulations, and turns off the check engine light.