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Severity: Low Code type: Generic (all makes)

P0405 Code: Exhaust Gas Recirculation Sensor A Circuit Low

The EGR position or pressure sensor signal is stuck near zero volts, below its normal operating range.

At a glance

Severity: 2/5 – Low2/5

Severity: Low

Meaning
Exhaust Gas Recirculation Sensor A Circuit Low
System
Emission Controls · Powertrain
Safe to drive?
Yes, short term
Typical repair cost
$80–$700
DIY difficulty
Easy

The EGR feedback sensor, a pintle position sensor on the valve or a DPFE differential pressure sensor on many Fords, is a three-wire sensor: the ECU sends it a 5-volt reference and a ground and reads back a signal that normally stays between roughly 0.5 and 4.5 volts. P0405 means that signal dropped below the lowest plausible value, usually close to 0 volts. That almost always has an electrical cause: a missing 5-volt reference, a signal wire that is broken or shorted to ground, or a sensor that has failed internally. Because the ECU can no longer see EGR flow or position, it normally stops using EGR until the fault is fixed.

Can I keep driving? Safe to drive; the engine normally runs fine. If other sensor codes appeared at the same time or the engine runs poorly, a shared 5-volt reference may be shorted and should be checked promptly.

How to read P0405

How to read P0405P10243054
  1. P Powertrain
  2. 0 Generic (SAE)
  3. 4 Auxiliary emission controls
  4. 05 Specific fault

Symptoms

  • Check engine light on
  • Usually no change in how the car drives
  • Light pinging under load because EGR has been switched off
  • Several sensor codes at once (MAP, throttle position) when a shared 5-volt reference is pulled down
  • EGR monitor stays 'not ready'

Possible causes

Ranked by how often each cause is behind this code (editorial estimate).

  1. Failed EGR position or DPFE sensor with an internal open or short 35%
  2. Broken signal wire or loose terminal at the sensor connector 22%
  3. 5-volt reference pulled low by a shorted sensor elsewhere on the same circuit 18%
  4. Signal wire chafed and shorted to ground against the engine or a bracket 15%
  5. Water in the connector causing a leak to ground 6%
  6. ECU fault on the reference or signal circuit 4%

Diagnosis step by step

Diagnostic flow: P04051Check for other 5-volt sensor codes2Read the sensor voltage key on,engine off3Measure reference and ground at theconnector4Isolate a shorted shared reference5Jumper test the signal wire6Repair, clear and confirm

  1. Check for other 5-volt sensor codes

    Look for MAP, throttle position or fuel tank pressure codes stored at the same time. Several low-voltage codes together point to a shared 5-volt reference being pulled down, and the EGR sensor may be the victim rather than the culprit.

    Tools: OBD-II scanner

  2. Read the sensor voltage key on, engine off

    Watch the EGR sensor PID with the key on. A healthy sensor rests at its baseline, typically somewhere around 0.5 to 1 V; a reading at or near 0 V confirms the low condition and tells you to start with the circuit tests.

    Tools: OBD-II scanner

  3. Measure reference and ground at the connector

    Unplug the sensor and measure between the reference pin and ground: you should see about 4.8 to 5.2 V. Then check the ground pin against battery negative; it should read near zero. No reference points to the wiring, a shorted sensor elsewhere or the ECU.

    Tools: Multimeter

  4. Isolate a shorted shared reference

    If the reference is low, unplug the other sensors that share it one at a time while watching the voltage. When it jumps back to 5 V, the sensor you just disconnected is shorting the circuit.

    Tools: Multimeter

  5. Jumper test the signal wire

    With the sensor unplugged and the key on, briefly connect the signal pin to the reference pin with a fused jumper. The scan tool should now show close to 5 V; if it does, the wiring and ECU are fine and the sensor is bad.

    Tools: Multimeter, OBD-II scanner

  6. Repair, clear and confirm

    Replace the sensor or repair the wire, clear the code and check that the sensor reading moves smoothly when the EGR valve opens during a drive. Make sure the EGR monitor completes before an emissions test.

    Tools: OBD-II scanner

Where the parts are

Ignition: coils and spark plugs per cylinder – P04051234567
Ignition: coils and spark plugs per cylinder
  1. 1Ignition coil
  2. 2Spark plug
  3. 3Fuel injector
  4. 4Camshaft sensor
  5. 5Crankshaft sensor
  6. 6Engine computer (ECM)
  7. 7Intake manifold

Repair options & costs

RepairDIY?Estimated cost
Replace DPFE sensor and hoses (Ford) Yes $90–$250
Replace EGR valve with integrated position sensor No $250–$700
Repair signal or reference wiring No $100–$300
Replace a shorted sensor on the shared 5-volt circuit Yes $80–$300

Rough US estimates for parts and labor; shop rates vary by region. Not a quote.

Notes by brand

Ford

On older Fords with a DPFE sensor, P0405 is a common sign that the sensor itself has failed electrically. The sensor sits on the firewall or near the EGR tube with two hoses to the exhaust; replace it with a quality part, since cheap copies often fail again quickly.

Field data

Chevrolet 3 Volt

Source: NHTSA Complaints API (US government open data), analyzed by DTC mention.

Emissions / smog test impact

Will fail

A stored P0405 with the check engine light on fails OBD-based smog checks. The EGR monitor won't run until the sensor reads normally, so the car can't pass until the circuit is repaired.

Frequently asked questions

What is 'sensor A' in P0405?

It's the primary EGR feedback sensor, usually the position sensor on top of the EGR valve or a separate differential pressure (DPFE) sensor. On most engines there is only one, so 'A' simply means that sensor.

Can a bad MAP sensor cause P0405?

Indirectly, yes. If the MAP sensor shorts internally and shares the same 5-volt reference, it can drag the reference down and make the EGR sensor read low as well.

Do I have to replace the whole EGR valve?

On many modern engines the position sensor is built into the valve, so yes. On older engines and Fords with a DPFE sensor, the sensor is a separate and much cheaper part.

Why is P0405 different from P0406?

P0405 means the signal is too low, which usually means an open signal wire, a lost reference or a short to ground. P0406 means too high, which points to an open ground or a short to voltage.

Sources