P0406Generic code

P0406 Code: Exhaust Gas Recirculation Sensor A Circuit High

The P0406 code means the signal from EGR valve position sensor A has gone above its maximum value. The main effect is that the EGR is switched off, with possible pinging and higher emissions. An open circuit, a loose connector or a broken sensor ground is the usual cause.

Severity
Medium
Can I keep driving?
Yes, no immediate risk
Estimated cost
$60 to $450
Difficulty
Medium
System
Emissions Control
Applies to
All OBD2 vehicles

Updated Reviewed by Renzo Chacca

On this page

What the P0406 code means

The EGR valve sends part of the exhaust gas back into the intake to lower combustion temperature and cut nitrogen oxides (NOx). On electronic valves, a position sensor tells the computer how far the valve is open.

The sensor gets a 5 volt reference and a ground from the computer and returns a signal between roughly 0.5 and 4.5 volts. The P0406 code sets when that signal is too high. That usually means an open circuit, such as a loose connector or a cut wire, or an interrupted sensor ground.

With the position signal lost, the computer cannot check the real opening and usually shuts the EGR off for safety. The engine runs, but you can get pinging under load, more NOx emissions and other EGR codes. Carbon building up in the valve is the underlying cause of many sensor failures.

To confirm it, measure the continuity of each wire between the component connector and the computer connector with the key off. It should be under 1 ohm, and an infinite reading means that wire is open. If the wiring is good, measure the component itself, because infinite resistance confirms it is open inside.

P0406 code symptoms

  • Check engine light on.
  • EGR switched off, with possible pinging and higher emissions.
  • Incomplete emissions monitor, so the vehicle cannot pass inspection.
  • Loss of power or rough running.

Likely causes of the P0406 code

  1. Loose or broken connector. This is the most frequent cause.
  2. Signal or ground wire cut. The signal rises up to the reference.
  3. Sensor open inside, with infinite resistance.
  4. Short to 5 volts or 12 volts from rubbing against another wire.

How to diagnose the P0406 code step by step

  1. Read the sensor value on the scan tool and compare it with what you expect.
  2. Inspect the connector for corrosion, water or loose pins.
  3. Check reference and ground with the key on: 5 volts, and less than 0.1 volt of drop on the ground.
  4. Measure the signal with the connector plugged in and see whether it changes with conditions.
  5. Do a wiggle test on the harness while watching the reading.
  6. Check continuity all the way to the computer.
  7. Compare desired and real position on the scan tool while you command the valve.
  8. Remove the valve and look for carbon. A stuck valve can distort the reading.

How to fix the P0406 code

  • Repair the connector or the wiring.
  • Replace the sensor if testing confirms it.
  • Correct the real condition if there is one, such as a leak or a blockage.
  • Clear the codes and complete a drive cycle so the monitor can run. If the P0406 code stays away, the repair worked.

Technical reference data

  • Valve closed: 0.3 to 0.9 volts.
  • Valve open: 4.0 to 4.5 volts.
  • These are approximate values, so check the manufacturer data for your engine.

Brand-specific notes

P0406 on Ford

On many Ford vehicles the sensor is built into the electronic EGR valve, and the whole assembly is replaced. On Ford diesels, carbon is the main cause.

P0406 on GM

On many GM vehicles the sensor is built into the electronic EGR valve, and the whole assembly is replaced.

P0406 on Nissan

On many Nissan vehicles the sensor is built into the electronic EGR valve, and the whole assembly is replaced.

P0406 on Volkswagen

On Volkswagen diesels, carbon is the main cause.

P0406 on Hyundai

On Hyundai diesels, carbon is the main cause.

Frequently asked questions about P0406

Can I drive with a P0406 code?
Yes. In general there is no immediate risk, and the problem is passing the emissions inspection.
Do I have to replace the sensor?
Only if testing confirms it. The connector and the wiring fail just as often as the sensor does.
Will I pass an inspection with this code?
No. The check engine light being on, or an incomplete monitor, keeps you from passing.
How much does it cost to fix P0406?
Roughly $60 to $450, depending on whether it is wiring, a connector or the valve assembly.
What does the P0406 code mean?
It is a generic OBD2 code for a high input in the EGR position sensor A circuit. The signal rose above its maximum value.
Will a P0406 code clear itself?
Only if the cause was a one-time glitch. An open wire or a failed sensor will bring the code back.
What is the most common cause of P0406?
A loose or broken connector, followed by a cut signal or ground wire. A sensor that is open inside is the next suspect.

Related codes

Questions about the P0406 code

There are no questions about this code yet. Tell us about your case: vehicle, symptoms and what you have already checked.