What is Mitsubishi OBD2 Code P1493?
When your Mitsubishi’s check engine light illuminates and a scan tool reveals the diagnostic trouble code (DTC) P1493, it indicates a specific fault within the Exhaust Gas Recirculation (EGR) system. This is a manufacturer-specific code, primarily for Mitsubishi vehicles, that points to a malfunction in the EGR valve’s feedback circuit or its position sensor. The EGR system is a critical emissions control component designed to reduce nitrogen oxide (NOx) emissions by recirculating a small, metered amount of exhaust gas back into the engine’s intake manifold. Code P1493 signals that the Powertrain Control Module (PCM) has detected an electrical or mechanical issue that prevents the EGR valve from operating within its expected parameters, potentially leading to increased emissions, reduced fuel economy, and drivability concerns.
Common Symptoms and Causes of P1493
Recognizing the symptoms associated with code P1493 is the first step in confirming the diagnosis. This code rarely appears in isolation and is often accompanied by noticeable performance issues.
Primary Symptoms of a P1493 Fault
- Illuminated Check Engine Light (MIL): The most immediate and obvious sign.
- Rough Idle or Stalling: Incorrect EGR flow can disrupt the air-fuel mixture at low engine speeds.
- Poor Engine Performance: Hesitation, lack of power, or sluggish acceleration, especially under load.
- Increased Fuel Consumption: The engine control unit may adjust fueling to compensate for the perceived fault.
- Failed Emissions Test: A malfunctioning EGR system will typically cause tailpipe emissions to exceed legal limits.
Root Causes of Mitsubishi Code P1493
The code P1493 is set when the PCM sees a discrepancy between the commanded position of the EGR valve and the actual position reported by its integrated sensor. The underlying causes typically fall into these categories:
- Faulty EGR Valve Position Sensor: The internal potentiometer or Hall-effect sensor within the valve assembly fails, providing an out-of-range, intermittent, or incorrect signal to the PCM.
- Clogged or Sticky EGR Valve: Carbon deposits from exhaust gas can build up on the valve pintle and seat, causing it to stick open, stick closed, or move sluggishly.
- Electrical Circuit Problems: This includes damaged, corroded, or shorted wiring harnesses and connectors for the EGR valve’s power, ground, or signal wires.
- Vacuum Supply Issues (on vacuum-operated valves): For older Mitsubishi models using vacuum-actuated EGR valves, a cracked vacuum hose, faulty vacuum solenoid, or a leak in the vacuum reservoir can prevent proper valve operation.
- Defective EGR Valve Solenoid: The electronic solenoid that controls vacuum or direct electric actuation of the valve may have failed.
- Rare PCM Failure: While uncommon, a malfunction within the engine control module itself cannot be entirely ruled out.
Step-by-Step Diagnostic Procedure for P1493
A systematic approach is essential to correctly diagnose and resolve a P1493 code. Avoid the temptation to simply replace the EGR valve without proper testing, as the root cause may be elsewhere in the circuit.
Step 1: Preliminary Inspection and Code Verification
Begin with a visual inspection. Check all wiring harnesses and connectors leading to the EGR valve for obvious damage, corrosion, or disconnection. Listen for vacuum leaks (hissing sounds) near the EGR valve and associated hoses. Use your OBD2 scanner to confirm the presence of P1493, clear the code, and perform a test drive to see if it returns immediately or under specific conditions (e.g., at operating temperature, under light acceleration).
Step 2: Testing the EGR Valve and Position Sensor
Consult your Mitsubishi service manual for the specific test procedure and pinout for your model’s EGR valve. Typically, you will need a digital multimeter (DMM).
- Resistance Check: Disconnect the valve’s electrical connector. Measure the resistance across the position sensor terminals. Compare the reading to the manufacturer’s specification (often a range, e.g., 1-5 kOhms). Move the valve pintle manually (if possible) and observe if the resistance changes smoothly without open circuits.
- Voltage Check: With the connector plugged back in and the ignition ON (engine off), back-probe the signal wire. You should see a reference voltage (often 5V) and a signal voltage that changes when the valve is commanded open via a scan tool.
Step 3: Checking the Control Circuit and Actuation
Using a scan tool with bidirectional controls, command the EGR valve to open and close at various percentages. Listen for a distinct clicking or humming sound from the valve, indicating it is receiving the command and attempting to move. If the valve is vacuum-operated, use a vacuum gauge to check for proper vacuum supply at the valve when commanded. A lack of sound or vacuum points to a circuit or solenoid issue.
Step 4: Physical Inspection and Cleaning
If electrical tests are inconclusive, remove the EGR valve from the intake manifold. Inspect the valve pintle and the passage in the intake for heavy carbon buildup. A valve that is physically stuck will confirm the fault. Often, careful cleaning with a specialized EGR/carburetor cleaner and a soft brush can restore proper function, provided the internal sensor is still operational.
Repair Solutions and Prevention
Once the root cause is identified, the repair path becomes clear. Following the correct procedure is vital for a lasting fix.
Common Repair Procedures
- Cleaning the EGR Valve and Passages: This is a cost-effective first step if carbon buildup is the sole issue. Ensure all carbon is removed and the valve moves freely before reinstalling with a new gasket.
- Replacing the EGR Valve Assembly: If the internal position sensor is faulty or the valve is severely corroded, replacement of the entire valve assembly is the standard repair. Always use a high-quality OEM or reputable aftermarket part.
- Repairing Wiring Harnesses: Repair any damaged wires with solder and heat-shrink tubing. Replace corroded connectors. Ensure all connections are secure and waterproof.
- Replacing Vacuum Components: For vacuum-operated systems, replace any cracked, brittle, or leaking hoses and test/replace the vacuum control solenoid.
Preventing a Recurrence of P1493
To minimize the chance of this code returning, adhere to a regular maintenance schedule. Using high-quality fuel and completing regular highway driving cycles can help keep the EGR system cleaner by burning off deposits. If you frequently drive short distances, occasional longer, higher-speed drives can be beneficial for the entire emissions system. After any repair, always clear all codes with your scan tool and perform a complete drive cycle to ensure the monitor runs and the code does not reset.
Conclusion
Mitsubishi OBD2 code P1493 is a specific and actionable diagnostic trouble code related to the EGR system’s feedback circuit. While it can cause noticeable drivability problems, it is typically repairable with a logical diagnostic approach. Starting with a visual inspection, progressing through electrical tests of the valve and its circuit, and finishing with a physical inspection will lead you to the root cause—whether it’s a simple carbon clog, a failed sensor, or an electrical fault. Addressing a P1493 code promptly not only restores your Mitsubishi’s performance and fuel efficiency but also ensures it remains compliant with emissions regulations.