Trouble code P1406 generally indicates a problem with the EGR (Exhaust Gas Recirculation) position sensor circuit. When the sensor signal is out of range or cannot be interpreted correctly, the ECU sets this fault and may activate limp mode.
If you're also researching related codes, you can check our P1400 diagnostic guide for comparison.
1. What P1406 Really Means
P1406 is triggered when the EGR valve position does not match the commanded value. This can be caused by carbon buildup, wiring resistance, or internal valve failure.
For technical reference, you can see EPA’s overview of EGR function: EPA Official Resource.
2. Common Symptoms
- Rough idle or unstable RPM
- Reduced engine power
- Check Engine Light (CEL) always ON
- Sluggish acceleration
- Possible increased fuel consumption
3. Most Likely Causes
- Carbon-clogged EGR valve
- Faulty EGR position sensor
- Open or shorted wiring harness
- Poor ground or corroded connector pins
- ECU software or signal interpretation issue (rare)
4. How to Diagnose P1406 (Technician-Level Steps)
Below is a practical step-by-step workflow commonly used in professional repair shops:
Step 1 — Scan with a Professional Diagnostic Tool
A bidirectional scanner such as the iCarsoft CR Ultra P allows you to check:
- EGR commanded vs actual position
- Live data deviations
- Wiring continuity values
- Whether other linked codes are also present
Step 2 — Check Wiring & Connectors
- Inspect the EGR connector for corrosion
- Check for damaged or hardened insulation
- Measure voltage supply and ground integrity
Step 3 — Inspect & Clean the EGR Valve
Carbon buildup is the most common reason. Remove the valve, clean deposits, and verify smooth actuator movement.
Step 4 — Test or Replace EGR Position Sensor
If the signal voltage is unstable or stuck, the sensor may need replacement.
Step 5 — Verify Repair & Clear the Code
Use the CR Ultra P to clear codes and confirm that the position tracks normally during a road test.
5. Recommended Tool — iCarsoft CR Ultra P
For P1406 and other EGR-related codes, the CR Ultra P offers:
- Full-system diagnostics
- Bidirectional control of the EGR actuator
- OE-level live data graphing
- WiFi updates (lifetime free)
- Support for a wide range of vehicle brands
- Available for U.S. & UK delivery
If you need help choosing the right scanner, you can reach us anytime through the chat box or email: service@icarsoft-us.com.
6. FAQ — Common P1406 Questions
Q1. Can I drive with a P1406 code?
You can, but it is not recommended. The engine may misfire or run poorly, and prolonged carbon buildup can damage the EGR system.
Q2. Does cleaning the EGR always fix P1406?
Cleaning solves the problem in many cases, but wiring faults and faulty sensors must not be ignored.
Q3. Why does P1406 return after clearing?
If the EGR position feedback signal is still incorrect, the ECU will reset the code within one or two drive cycles.
Q4. Which scanner can control the EGR valve for testing?
The iCarsoft CR Ultra P supports EGR actuator tests on most makes, including the full 4.0 series coverage plus two additional brands.
Q5. Is the CR Ultra P updated free for life?
Yes — WiFi updates are free and automatic.
7. Summary
P1406 is typically caused by a restricted EGR valve, faulty position sensor, or wiring issue. A proper scan and actuator test using the CR Ultra P helps confirm the failure quickly and avoid unnecessary part replacements.
