OBD2 Code P1476: EVAP Leak Detection Pump Control Circuit Explained

Understanding the P1476 Diagnostic Trouble Code

The OBD-II diagnostic trouble code (DTC) P1476 is a manufacturer-specific code, most commonly associated with Chrysler, Dodge, Jeep, and Ram vehicles, though it can appear in others. It is defined as “EVAP Leak Detection Pump Control Circuit”. This code indicates a malfunction within the electrical control circuit of the vehicle’s Evaporative Emission Control (EVAP) system, specifically the component responsible for actively testing the system for leaks: the Leak Detection Pump (LDP). Unlike codes pointing to a physical leak (like a small or large leak), P1476 focuses on the computer’s ability to command and monitor the pump itself.

Role of the EVAP System and Leak Detection Pump

The EVAP system is a critical emissions component 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 self-diagnostic tool. During specific drive cycles, the Powertrain Control Module (PCM) activates the LDP. The pump pressurizes the EVAP system with air and then monitors the pressure decay to determine if a leak is present. A fault in its control circuit prevents this test from occurring or being interpreted correctly.

How the PCM Triggers Code P1476

The PCM monitors the Leak Detection Pump circuit for expected voltage values and electrical continuity. When it sends a command to activate or deactivate the LDP (via a solenoid inside the pump), it expects to see a corresponding change in the circuit’s state. If the PCM detects an open circuit, short to ground, short to power, or an unexpected voltage reading that does not align with its command, it will log code P1476 and illuminate the Check Engine Light (MIL). The code is set when the fault is detected in two consecutive drive cycles.

Symptoms, Causes, and Diagnosis of P1476

A vehicle with a stored P1476 code may exhibit subtle symptoms or none at all related to drivability, as the issue is primarily electrical and diagnostic. However, the underlying cause will prevent the EVAP system from completing its self-check, which can lead to failed emissions tests.

Common Symptoms of a P1476 Fault

Illuminated Check Engine Light (MIL): This is the most frequent and often the only symptom.
Failed Emissions Inspection: The vehicle will not pass a state emissions test due to an incomplete EVAP monitor.
Other EVAP Codes: Possible presence of secondary codes like P0442 (small leak) if the diagnostic test cannot run.
Rough Idle (Less Common): In some cases, a stuck-open LDP solenoid could potentially affect engine vacuum.

Primary Causes of the P1476 Code

Faulty Leak Detection Pump (LDP): The internal solenoid or pump mechanism has failed. This is a very common cause.
Damaged Wiring or Connectors: Corroded, broken, frayed, or shorted wires in the LDP control circuit harness.
Poor Electrical Connections: A loose or corroded connector at the LDP or PCM.
Blown Fuse: A fuse supplying power to the EVAP system or PCM may be blown.
Defective Powertrain Control Module (PCM): Rare, but a failed PCM driver circuit for the LDP is possible.

Step-by-Step Diagnostic Procedure

Warning: Always consult vehicle-specific service information for wiring diagrams, connector locations, and test values. Safety first: ensure the engine is cool and the vehicle is securely supported.

Step 1: Visual Inspection. Locate the Leak Detection Pump (often near the charcoal canister or fuel tank). Inspect the wiring harness and connector for obvious damage, corrosion, or disconnection.
Step 2: Check the Fuse. Verify the fuse for the EVAP system or PCM (refer to the owner’s manual) is intact.
Step 3: Test the LDP Solenoid. Using a digital multimeter (DMM), check the resistance of the LDP solenoid across its two electrical terminals. Compare the reading to the manufacturer’s specification (often between 10-30 ohms). An open (infinite resistance) or short (near 0 ohms) indicates a bad pump.
Step 4: Circuit Voltage Tests. With the connector disconnected and the ignition ON, check for reference voltage (typically 12V) at the harness side. Check for continuity of the ground and control wires back to the PCM.
Step 5: Actuation Test. Using a bidirectional scan tool, command the LDP ON and OFF. You should hear/feel a distinct click from the pump. No click suggests a faulty pump or a wiring issue preventing the command.

Repair Solutions and Technical Considerations

Once the root cause is identified through methodical diagnosis, the repair can be targeted and effective. Avoid the common mistake of replacing the Leak Detection Pump without first verifying the integrity of the wiring and power supply.

Repairing Wiring and Connector Issues

If the diagnosis points to a wiring fault, repair is mandatory. Solder and heat-shrink tubing are the preferred methods for splicing wires. Never use “twist and tape” connections in automotive environments, as they are prone to corrosion and failure. For corroded connectors, specialized electrical contact cleaner and dielectric grease are essential. Ensure all repairs are sealed from moisture.

Replacing the Leak Detection Pump

If the LDP is confirmed faulty, replacement is straightforward. The pump is usually held by one or two bolts and has a vacuum hose and an electrical connector.

Disconnect the negative battery cable as a safety precaution.
Disconnect the electrical connector and vacuum hose(s).
Unbolt the pump and remove it.
Install the new pump, reconnect the hose and connector, and secure the bolts.
Reconnect the battery.

Important: After any repair for P1476, you must clear the code with an OBD2 scanner. The vehicle will then need to complete a specific “drive cycle” for the EVAP monitor to run and pass. This may involve a mix of city and highway driving under certain fuel level and temperature conditions.

When to Suspect a PCM Issue

PCM failure is a last-resort diagnosis. Only consider it if:

All wiring tests confirm perfect continuity and correct voltage to/from the PCM connectors.
The LDP tests good for resistance and can be actuated with direct 12V power.
All fuses and grounds are confirmed good.
The scan tool cannot communicate with the PCM’s LDP driver circuit during an actuation test.

Reprogramming or replacing a PCM is a complex task often requiring professional equipment and vehicle-specific programming.

Conclusion

Code P1476 is a circuit-specific fault that disables your vehicle’s ability to self-diagnose fuel vapor leaks. While it rarely causes performance problems, it will keep the Check Engine Light on and cause an emissions test failure. Successful repair hinges on a logical diagnostic approach: start with a thorough visual inspection, then proceed to electrical testing of the Leak Detection Pump and its associated wiring before condemning any components. By following the technical steps outlined, DIY mechanics and technicians can efficiently resolve this common EVAP system electrical fault and restore full system functionality.