P0405🌫 Emissions / EGR (exhaust gas recirculation) systemDrive with caution, fix soon

P0405: EGR Sensor A Circuit Low (Meaning, Causes, Fixes)

Reviewed 2026-10-25 · Based on 2 cited source(s)

What P0405 means

The EGR valve lets a measured amount of exhaust gas back into the cylinders to lower combustion temperatures and cut NOx (oxides of nitrogen) emissions. A feedback circuit tells the PCM whether the EGR valve is actually moving as commanded. OBD-Codes.com says P0405 may set if that feedback circuit voltage is unusually low, or the valve's position reads lower than it was commanded to be. RepairPal says P0405 means the EGR valve position sensor is giving low voltage readings, usually below the 0.5 to 1.0 volt range, and that the code can set during normal driving or while the EGR OBD-II monitor runs. The sources differ in scope: OBD-Codes.com treats it as an electrical feedback-circuit fault (shorts, bad valve, PCM), while RepairPal's cause list is broader and also includes the DPFE (differential pressure feedback EGR) sensor, a carbon-clogged or stuck valve, and vacuum or solenoid problems. They also differ on symptoms: OBD-Codes.com lists only the check engine light, while RepairPal adds possible pinging under load. Related codes include P0400 to P0404 (EGR flow and control circuit) and P0406 (sensor A circuit high).

Severity: can I keep driving?

Drive with caution, fix soon

Usually safe to drive for now, but get it diagnosed within a reasonable time. RepairPal rates P0405 Moderate: it may not threaten safety or drivability right away, but it should be fixed to keep the car running well. OBD-Codes.com lists only the check engine light as a symptom, while RepairPal says some cars may ping (knock) on acceleration or under load. Persistent pinging can harm the engine, and the car will likely fail an emissions test with the light on.

Common symptoms

Likely causes

Roughly most to least common, based on the sources below. Your vehicle may differ.

  1. Short to ground in the EGR signal or 5 volt reference circuit (OBD-Codes.com)
  2. Short to voltage in the EGR ground or signal circuit (OBD-Codes.com)
  3. Chafed wiring or loose terminals, or a bad EGR position sensor connector (OBD-Codes.com; RepairPal)
  4. Bad EGR valve, or a defective EGR valve position sensor (OBD-Codes.com; RepairPal)
  5. Defective DPFE sensor or its wiring (RepairPal)
  6. EGR valve stuck closed or full of carbon (RepairPal; OBD-Codes.com notes carbon or frozen moisture can make a valve stick)
  7. Lack of proper vacuum or electrical signal to the EGR valve, or a bad EGR vacuum supply solenoid (RepairPal)
  8. Bad PCM, rarely; OBD-Codes.com says other codes will likely be present if so

Diagnostic steps you can do

⚠ Before you start

Work on a cool engine, parked on level ground with the parking brake set. Never work under a car supported only by a jack.

  1. Read all stored codes with a scan tool and note any other EGR codes (P0400 to P0406) that came with it.
  2. Inspect the EGR valve connector and wiring for chafing, corrosion or loose terminals (OBD-Codes.com; RepairPal).
  3. On vacuum-controlled systems, check the vacuum hoses to the EGR valve and solenoid for cracks or disconnections (RepairPal lists lack of proper vacuum).
  4. If the code showed up in very cold weather, note that OBD-Codes.com says moisture can freeze in the valve and make it stick until the engine warms up.
  5. Clear the code and see if it returns; OBD-Codes.com says if the valve responds to scan-tool commands and feedback looks right, the problem may be intermittent.

Typical fixes

Repair costs vary widely by vehicle, region, parts brand and shop, so we don't quote prices. Get a written estimate after diagnosis.

🛠 When to call a pro

  • Commanding the EGR valve on with a scan tool and watching the position feedback (OBD-Codes.com)
  • Checking for 5 volts on the EGR reference wire key on, engine off, and test-light checks for shorts or opens (OBD-Codes.com)
  • Jumpering the 5 volt reference to the signal circuit; the scan tool should then read 100 percent EGR position (OBD-Codes.com)
  • Comparing EGR position data with MAP and other feedback during the EGR monitor's drive conditions (RepairPal)
  • The code returns after wiring repairs, or other PCM codes are present

Where to buy

Plain search links. Always match parts to your exact year, make, model and engine.

OBD2 scanners on Amazon Parts at Advance Auto Parts catalog at RockAuto

FAQs

Is P0405 serious?

RepairPal rates it Moderate, so it usually isn't an immediate safety issue, but it should be diagnosed within a reasonable time. OBD-Codes.com lists only the check engine light as a symptom; RepairPal says some cars may ping under load, which is worth fixing before it harms the engine.

Does P0405 mean I need a new EGR valve?

Not always. OBD-Codes.com's diagnosis checks the 5 volt reference and signal wiring first and says to replace the EGR valve only if the wiring is okay. RepairPal also lists the position sensor, DPFE sensor, carbon buildup and vacuum problems as possible causes.

What is the difference between P0405 and P0406?

Both are about EGR sensor "A". According to the related-code lists on OBD-Codes.com and RepairPal, P0405 is sensor A circuit low and P0406 is sensor A circuit high.

How much does it cost to fix P0405?

Neither source gives a repair cost. It can range from fixing a chafed wire or cleaning carbon to replacing the EGR valve or a sensor, so get a diagnosis and a written estimate first.

Sources

  1. OBD-Codes.com: P0405 EGR Sensor A Circuit Low (Dale Toalston, ASE)
  2. RepairPal: P0405 Exhaust Gas Recirculation Sensor "A" Circuit Low (rated Moderate)

Last reviewed 2026-10-25. Code definitions and repair steps can vary by manufacturer. Confirm with your vehicle's service information.