OBD II fault codes

DTC P0406

02.11.2025
Author:Ihor Koziar. Reviewed by:Inna Semenko
eye4704
clock6 minutes of reading
Enter the error code and car brand
Brand
logo
P0406
Vehicle engine and/or automatic transmission
Code: P0406 - The Exhaust Gas Recirculation (EGR) valve position sensor A is showing a signal that is too high, which may affect emissions and engine performance.

Whenever I come across the p0406 code in the shop, I know the PCM-the car’s main computer-is picking up a voltage from the EGR position sensor that’s way higher than it should be. Here’s the deal: the EGR system recirculates some exhaust back into the engine to keep emissions low and help the motor run smoother. The position sensor is the eyes and ears for the PCM, constantly reporting how far open or shut the EGR valve is. If the signal jumps way above normal, the PCM throws the P0406 code and flips that check engine light. In other words, your car’s trying to tell you, “Something’s off with the EGR system-let’s take a look.”

Common Causes for P0406 code

From my time under the hood, I can tell you-most p0406 issues boil down to a handful of usual suspects. Here’s what I run into most often:

  • The EGR valve position sensor gives up the ghost, sending bad info to the computer.
  • The EGR valve itself sticks open or fails inside, which throws everything out of whack.
  • Wiring problems-cracked insulation, corroded pins, or a connector that just isn’t seated right. That can send the PCM on a wild goose chase.
  • On rare occasions, the PCM itself could have outdated software or an internal problem.

In my experience, it’s almost always the sensor or the wiring. Still, I always double-check everything-especially with Chrysler dtc p0406, Dodge dtc p0406, or Jeep dtc p0406-since these brands can all see this error pop up.

Warning Signs and dtc P0406

When dtc p0406 shows up, most folks notice their car doesn’t drive quite right. Here’s what you’re likely to see:

  • The check engine light-always your first warning.
  • If you take your car for an emissions test, expect it to fail; the EGR system isn’t doing its job and NOx numbers go up.
  • Listen for pinging or knocking, especially when you’re climbing a hill or accelerating.
  • Fuel economy drops, and you’re visiting the gas station more than usual.
  • Occasionally, the engine will stall or hesitate, especially when you’re idling at a light.

Sometimes, it’s only the check engine light. But trust me-ignore it, and things can spiral fast.

logo

Steps for Diagnosing P0406

Here’s how I tackle a P0406 code in the shop, and you can follow these steps if you’re comfortable with DIY diagnostics:

  • First off, make sure your battery’s topped up and the workspace is safe. You don’t want surprises while poking around under the hood.
  • Take a good look at the EGR valve and its wiring. Check for busted insulation, loose connections, and corrosion. A classic mistake I see? People skip checking the connector-sometimes it’s just not clicked in all the way.
  • Grab a scan tool and watch the live data from the EGR position sensor. If you see the voltage stuck high (over 4.5 volts), that’s a smoking gun.
  • Using a multimeter, back-probe the sensor’s signal wire and compare your reading to the manual’s spec. If it’s too high, unplug the sensor and see if it drops. If it does, you’ve probably found the culprit.
  • Trace the wires back to the PCM. Look for shorts to power or ground, and gently move the harness while watching the scan tool-sometimes a wiggle is all it takes to uncover an intermittent fault.
  • If the sensor and wiring pass your tests, pull the EGR valve and inspect for sticking or internal failure.
  • Only suspect the PCM if you’ve ruled everything else out-it’s almost never the cause, but don’t ignore it if you’re stumped.

I always recommend having a buddy nearby to help hold wires or monitor readings-two sets of eyes beat one every time.

dtc p0406

Avoiding obd2 code P0406 Troubleshooting Errors

Let me share some pitfalls I see all too often when folks chase down this code:

  • Jumping straight to swapping out the EGR valve or sensor before checking the wiring. I’ve seen countless sensors replaced when the real problem was just a crusty connector.
  • Skipping simple stuff like checking fuses and ground connections. These can trip you up in no time.
  • Not using a scan tool to read real-time data-this is a huge time-saver and can zero in on the issue fast.
  • Overlooking intermittent wiring issues. Wiggle the harness and watch the readings-you might catch a glitch that only shows up occasionally.

Here’s a pro-tip from the garage: always start with the basics before shelling out for expensive parts. It’ll save you headaches and cash.

logo

How Serious is a P0406 trouble code

P0406 isn’t something you want to let slide. Sure, the engine might still run for now, but a bad EGR sensor or valve can ramp up emissions, eat into your wallet with poor mileage, and even risk engine damage if you ignore it. Pinging and stalling are more than just annoyances-they’re safety risks, especially in heavy traffic. And don’t count on passing that next emissions test. Leave it unchecked and you could end up with fried pistons, burned valves, or a trashed catalytic converter. I’ve seen engines wrecked by what started as a simple sensor problem. Take it from me: deal with this code before it gets ugly.

Recommended P0406 engine code Repairs

Here’s my go-to fix list for P0406, based on what’s worked in the shop and what the factory recommends:

  • Swap out the EGR valve position sensor if it’s giving bad readings.
  • Fix or replace any busted wires or connectors you find in the EGR circuit.
  • If the EGR valve is sticky or jammed, clean it out or change it.
  • Check for software updates on the PCM-sometimes there’s a factory bulletin that addresses the problem.
  • Clear the code, take the car for a spin, and confirm the fix holds up.

Start with the sensor and wiring-nine times out of ten, that’s where the problem hides.

Conclusion

So, what’s the bottom line? P0406 means your car’s computer doesn’t like what it’s hearing from the EGR position sensor-usually thanks to a bad sensor, wiring issue, or a sticky EGR valve. Ignore it, and you’re asking for bigger trouble: rough running, failed emissions, and maybe even engine damage. My advice? Check the wiring and connectors first, test the sensor, and only move on to the valve or PCM if necessary. A methodical, step-by-step approach will get your car back in shape and save you from expensive repairs down the road. Trust your instincts, use the right tools, and don’t rush-your ride will thank you.

The following error codes are often searched for
P0116P0117P0118P0120P0121P0122P0123P0125P0128P0130P0131P0132P0133P0134P0135P0136P0137P0138P0139P0140
Comments on the article