Fix P0406: Mechanic’s solutions that WORKED

The P0406: Exhaust Gas Recirculation Sensor A Circuit High indicates a high voltage error in the EGR (Exhaust Gas Recirculation) Sensor A Circuit, pointing to a malfunction in the EGR system, often caused by a faulty EGR valve or related components. This issue can lead to poor engine performance, increased emissions, and potential damage if left unaddressed.

P0406 quick overview

Meaning	P0406: Exhaust Gas Recirculation Sensor A Circuit High
Is it serious?	This code can lead to engine performance issues and increased emissions, thus requiring timely attention.
Possible causes	Faulty or malfunctioning EGR valve Damaged or corroded wiring/connections to EGR valve Clogged or restricted EGR passages Potential issues with the Powertrain Control Module (PCM)
How to diagnose?	Inspect EGR Valve: Check for any visible damage or malfunction. Check Wiring and Connectors: Examine the electrical connections for damage or corrosion. Test EGR Operation: Use diagnostic tools to assess the functioning of the EGR valve. Clean EGR Passages: Ensure there are no blockages in the EGR system. Consult Diagnostic Tools: Use a scanner to read and interpret diagnostic data. Consider PCM Update: Check if a PCM software update is necessary.

How to fix P0406 – learn from mechanics

I looked into P0406 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: Dodge

Vehicle Information: 2008 Dodge Ram 1500 ST 5.7L – MIL Lamp on

Issue + Repair History:

• Initially had a P0404 code.
• After clearing the code, it returned a few days later with P0406.
• EGR operation was checked using a diagnostic tool, along with wiring, and found to be working.
• The truck also had an issue with the pipe between the catalytic converter and muffler blowing off.

Other OBD2 Codes + Test Results:

• P0404
• P0406

Suggestions to Fix Issue:

• Check for any restriction in the exhaust system, as excess pressure might be causing more flow than expected.
• Perform backpressure and vacuum tests to determine system efficiency.
• Replace the EGR valve, considering the possibility of internal solenoid windings failure.
• Disconnect the battery for 5 minutes to fully clear the adaptives, as per a Chrysler tech tip.
• Inspect for a clogged or restricted muffler.
• Explore the need for a PCM update and verify the voltage at the EGR valve.

Final Fix:

• Replaced the EGR valve.
• The customer opted for a Flowmaster exhaust replacement, addressing the issue with the exhaust system.
• These replacements resolved the issues satisfactorily.

Case #2: Chevrolet

Vehicle Information: 1996 Chevrolet K1500 6.5L – MIL Lamp on

Issue + Repair History:

• Encountered a P0406 code indicating EGR sensor circuit high.
• Uses a MAP sensor to monitor vacuum to EGR.
• Observed vacuum at EGR: 7″ at idle, 20″ during light throttle driving, and drops to 0″ when turbo builds boost.
• Scanner showed desired EGR duty cycle at 80%, but actual was 0%.

Computer Codes & Descriptions:

• P0406 – EGR voltage high

Suggestions to Fix Issue:

• Check the vacuum pump for proper functioning and inspect for any cracked vacuum lines.
• Examine the sensor or connecting wiring for faults, checking the connector for corrosion and the vacuum line for soot or obstructions.
• Consider if the vacuum at idle is too low (should be at least 14″) and the possibility of a worn or shiny pulley or belt. If these are fine, consider replacing the vacuum pump.

Final Fix:

• The problem was an intermittent vacuum solenoid, not the duty cycle solenoid.
• Identified a vacuum supply solenoid issue, which failed after the third diagnostic attempt.
• Replacing the vacuum supply solenoid resolved the issue.

Case #3: GMC

Vehicle Information: 2013 GMC Sierra 2500 HD SLE 6.6L – MIL Lamp on

Issue + Repair History:

• Vehicle experienced issues in cooler temperatures (around 40 degrees or less), but was not acting up during diagnosis at higher temperatures (60-65 degrees).
• Recent history codes as of 10/31/16: P06A3, P0406, P140B, P24C4, P046C, P2493.
• Related repairs: PCM software update (10/14/16), reductant tank heater replaced (10/26/16).
• The issue remained unresolved as of the last update on 12/15/16 due to the time limit for open help requests being exceeded.

Computer Codes & Descriptions:

• P06A3: 5-volt reference 4 circuit.
• P0406: EGR position sensor circuit high voltage.
• P140B: EGR slow response – increasing flow.
• P24C4: Undocumented code – EGR cooler bypass exceeded learning limit.
• P046C: EGR position sensor performance.
• P2493: EGR cooler bypass position sensor.

Suggestions to Fix Issue:

• Diagnose the 5-volt reference 4 circuit P06A3 for potential shorts to ground, rubbed wires, or high resistance.
• Inspect the EGR and fuel temp sensor 2 on the 5-volt reference circuit.
• Check the low reference circuits.
• Investigate the EGR cooler for potential clogging.
• Ensure the fuel temp sensor isn’t leaking fuel in the connector.
• Verify if all the EGR passages are clear and open.

Final Fix:

• Installed an EGR bypass valve, which resolved the concerns.

Case #4: Pontiac

Vehicle Information: 2008 Pontiac Torrent 3.4L – MIL, trac, and StabiliTrac lights on

Issue + Repair History:

• Found P0404 code for EGR.
• All circuits checked, EGR valve replaced.
• Issue persisted; when commanding the EGR valve over 10%, it clicked rapidly, and the position and command percentage fluctuated.
• At 90% EGR command, the engine stalled.
• Initially replaced EGR valve with a Standard brand valve.

Computer Codes & Descriptions:

• P0404: EGR Open Position Performance

Suggestions to Fix Issue:

• Check engine’s response when EGR is fully opened; assess if EGR passages are restricted.
• Test exhaust backpressure during cruise for potential restriction in the exhaust system.
• Ensure adequate exhaust flow to and from the EGR; check for blockages.
• Confirm if the EGR valve is OEM and properly oriented.
• Consider replacing the EGR valve with a different brand or OEM part.
• Inspect for bad connections at the EGR valve connector.
• Check for harness problems leading to the EGR valve.

Final Fix:

• Replaced the EGR valve with a new OE (Original Equipment) valve, which fixed the problem.

Case #5: Dodge

Vehicle Information: 2005 Dodge Magnum SXT 3.5L – Stall, MIL Lamp on

Issue + Repair History:

• Lack of sufficient information for diagnostic procedures.
• Vehicle is a fleet vehicle with no available history.

Computer Codes & Descriptions:

• P0406: EGR Circuit Malfunction

Suggestions to Fix Issue:

• Replace the EGR valve; a common issue with this model is the internal sense circuit going bad, triggering the code.
• Consider reprogramming the PCM (Powertrain Control Module) as a complementary measure.
• Utilize diagnostic resources like Alldata for detailed diagnostic procedures, referencing similar models such as the 2004 Dodge Intrepid 3.5L.

Final Fix:

• Replaced the EGR valve and gasket, which resolved the issue with the engine light and stalling.

Advice	Description of Diagnostic Step
Replace EGR Valve	The most common fix; involves replacing the EGR valve as it often malfunctions internally.
Check for OEM Parts	Ensure the replacement EGR valve is an OEM (Original Equipment Manufacturer) part for better compatibility and performance.
Inspect Wiring and Connections	Examine the wiring and connections to the EGR valve for any shorts, corrosion, or bad connections.
Test EGR Operation	Verify the operation of the EGR valve, checking for any erratic behavior or stalling when activated.
Check for Restricted Passages	Inspect EGR passages for any blockages or restrictions that could affect valve function.
Verify Vacuum and Exhaust Flow	Ensure adequate vacuum and exhaust flow to and from the EGR valve.
Reflash or Update PCM (if applicable)	In some cases, updating or reprogramming the Powertrain Control Module may be necessary.
Perform Comprehensive Diagnostic Testing	Use diagnostic tools like scanners to comprehensively test the EGR system and related components.