Fix P0405: Mechanic’s solutions that WORKED

Code P0405 stands for “Exhaust Gas Recirculation (EGR) Sensor A Circuit Low.” It indicates that the electrical circuit for the EGR sensor is detecting a lower-than-expected voltage, most often caused by faulty or clogged EGR valve or other EGR system components.

P0405 quick overview

Meaning	P0405: Exhaust Gas Recirculation (EGR) Sensor A Circuit Low
Is it serious?	While not extremely serious, it should be addressed to prevent potential issues related to emissions and engine performance.
Possible causes	– Wiring or connector issues in the EGR circuit – Faulty EGR sensor – EGR valve malfunction – Poor-quality or contaminated fuel – Carbon buildup in EGR passages – EGR cooler problems (especially in modified vehicles)
How to diagnose?	Check Wiring and Connectors: Inspect the wiring and connectors associated with the EGR system, looking for damage, corrosion, or loose connections. Perform a Capacitor Discharge: If problems persist, perform a capacitor discharge by touching the positive and negative battery cables together to clear stored values in the PCM. Verify Fuel Quality: Ensure the fuel quality is good, especially if issues began after refueling. Poor-quality or contaminated fuel can contribute to EGR-related problems. Inspect EGR Passages: Examine the EGR passages for blockages or carbon buildup, which can hinder EGR valve operation. Clean or replace components as necessary. Consider EGR Cooler Delete: In cases of recurring EGR-related issues, contemplate an EGR cooler delete, particularly if the vehicle has been modified with a tuner or chip that disables EGR. Test EGR Components: Test the EGR valve and sensor using appropriate diagnostic equipment to ensure they are functioning as intended.
What is EGR valve?	An EGR (Exhaust Gas Recirculation) valve is a component in a vehicle’s engine that recirculates a portion of exhaust gases back into the engine’s combustion chamber to reduce emissions and control combustion temperature.

How to fix P0405 – learn from mechanics

I looked into P0405 service cases at iatn.com website where in the private forums the mechanics seek advice from other mechanics. I looked up a bunch of cases to help you decide how to fix your issue and see what would a real mechanic do to solve it.

Case #1: Cadillac

Vehicle Information:
2002 Cadillac Seville STS 4.6L

Issue + Repair History:
The car had a water pump crossover housing leak and two codes: P0171 and a dead O2 sensor. Repaired the water pump, crossover housing, and O2 sensor. After a test drive, the SES light came on with code P1404. Replaced the EGR valve and rewired it, but the code P1404 remained.

Other OBD2 Codes + Test Results:
No other codes mentioned.

Suggestions to Fix Issue:\

1. Check for EGR passage blockage.
2. Ensure the EGR valve is not mounted backward, causing exhaust pressure on the pintle.
3. Disconnect the battery and short the cables for about ten minutes to reset the EGR valve’s closed position, allowing the PCM to relearn on startup.

Final Fix:
Reversed the EGR valve, solving the issue. (Installed backwards originally)

Case #2: Dodge

Vehicle Information:
2005 Dodge Ram 1500 ST 4.7L

Issue + Repair History:
The customer brought in the vehicle with a check engine light on and a complaint of stalling. Scanned and retrieved trouble codes PO404 (EGR Position Sensor Performance) and PO405 (EGR Position Sensor Circuit Low). Replaced the EGR Valve Assembly from the Dodge dealership, but the check engine light came back on with code PO405 after a test drive.

Other OBD2 Codes + Test Results:
No other codes mentioned.

Suggestions to Fix Issue:\

1. Disconnect the battery after EGR Assembly replacement to reset PCM’s learned values.
2. Check all EGR circuit wires for shorts and opens.
3. Ensure the software is up to date.
4. Check EGR passages for clogs.
5. Verify the seals are in good condition.
6. Consider a PCM reflash if necessary.

Final Fix:
Disconnecting the battery after EGR Assembly replacement to reset the PCM’s learned values resolved the issue.

Case #3: Jeep

Vehicle Information:
2007 Jeep Wrangler X 3.8L

Issue + Repair History:
Customer reported a check engine light. Tested all voltages and grounds to the EGR valve, all readings were good. Replaced the EGR valve, but the code (P0405) reset on the first trip.

Suggestions to Fix Issue:\

1. Disconnect the battery to reset counters.
2. Check all wiring to the EGR valve, ensuring there are no shorts or opens.
3. Confirm the EGR passages are clear.
4. Consider a software flash update to the PCM (if available).

Final Fix:
The issue was resolved by disconnecting the battery to reset counters, indicating a need to clear the PCM’s learned values.

Case #4: Chevrolet

Vehicle Information:
2001 Chevrolet Astro LS 4.3L

Issue + Repair History:
The vehicle came in with a symptom of not being able to idle, which the customer reported occurred after filling up with gas. The fuel pressure and charging system were checked, and they both passed. Two trouble codes were retrieved: P0405 (EGR recirculation sensor “A” circuit low) and P0404 (EGR recirculation control circuit range performance).

The following repairs were attempted:

1. Changed the fuel filter.
2. Replaced the MAP sensor.
3. Replaced the throttle position sensor.
4. Replaced the EGR valve.

Suggestions to Fix Issue:\

1. Verify the quality of the fuel, as incorrect or contaminated fuel may cause issues.
2. Check for the presence of excessive ethanol or methanol in the fuel, which could affect engine performance.
3. Inspect for water contamination in the fuel.
4. Perform an exhaust back pressure test to check for a clogged catalytic converter.

Final Fix:
After conducting a thorough investigation, it was determined that the PCM (Powertrain Control Module) had failed. Replacing the PCM and re-flashing the system resolved the issue. The cause of the PCM failure was not identified.

Case #5: Ford

Vehicle Information:
2007 Ford E-350 Super Duty 6.0L

Issue + Repair History:
The vehicle had a fault code P0405 (EGR circuit low). The voltage with the key on engine off was 0.59 volts. The following steps were taken to diagnose and resolve the issue:

1. Checked reference voltage (5 volts) and ground.
2. Jumpered light blue/orange signal with reference voltage.
3. Observed a 5-volt signal on the scanner.
4. Performed EGR activation, and the voltage went up as the valve opened.
5. When driving, the EGR voltage did not change.
6. Looked at the MAP, barometric pressure, and backpressure sensor, which were within spec.
7. Customer had upgraded the FICM (“Fuel Injector Control Module) to 52 volts, and this caused code P0611 (FICM performance).

Suggestions to Fix Issue:\

1. Check for any air leaks after the MAF before the turbo.
2. Verify that the intake is connected properly.
3. Check the EGR system test using a scan tool.
4. Inspect the EGR valve for carbon buildup and replace if necessary.
5. Investigate the wiring and connectors for the EGR actuator and sensors.
6. Consider the possibility of an EGR cooler delete and its impact on the system.

Final Fix:
The code P0405 did not return after installing a new EGR valve. The issue with not seeing EGR valve activation while driving was not resolved, and it may be related to the engine not reaching the necessary temperature for activation. The customer picked up the vehicle, and further feedback was expected.