P0405Generic code

P0405 Code: Exhaust Gas Recirculation Sensor A Circuit Low

The P0405 code means the signal from EGR valve position sensor A has dropped below its minimum value. The main effect is that the EGR is switched off, with possible pinging and higher emissions. A signal wire shorted to ground or a missing 5 volt reference 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

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What the P0405 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 P0405 code sets when that signal is too low. That usually means the signal wire is shorted to ground or the reference is missing.

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, unplug the component with the key on and watch what happens to the reading or the code. If the value jumps to the opposite extreme, the wiring is fine and the component is the one pulling the signal to ground. If nothing changes, look for the short in the wire, starting where the harness rubs against the engine, the chassis or the exhaust.

P0405 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 P0405 code

  1. Signal wire shorted to ground by rubbing or heat.
  2. 5 volt reference shorted, if other sensors also fail.
  3. Damaged sensor with an internal short.
  4. Connector with water in it. This is very common on sensors mounted low on the vehicle.

How to diagnose the P0405 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 P0405 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 P0405 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

P0405 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.

P0405 on GM

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

P0405 on Nissan

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

P0405 on Volkswagen

On Volkswagen diesels, carbon is the main cause.

P0405 on Hyundai

On Hyundai diesels, carbon is the main cause.

Frequently asked questions about P0405

Can I drive with a P0405 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 P0405?
Roughly $60 to $450, depending on whether it is wiring, a connector or the valve assembly.
What does the P0405 code mean?
It is a generic OBD2 code for a low input in the EGR position sensor A circuit. The signal fell below its minimum value.
Will a P0405 code clear itself?
Only if the cause was a one-time glitch. A shorted wire or a failed sensor will bring the code back.
What is the most common cause of P0405?
A signal wire shorted to ground, or water in the connector. Carbon in the valve is behind many sensor failures.

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