Fix P0402: Mechanic’s solutions that WORKED

The code P0402: EGR Excessive Flow indicates an irregularity in the Exhaust Gas Recirculation (EGR) system, particularly when there’s too much EGR flow. It’s often linked to issues with the EGR valve, the Mass Airflow (MAF) sensor, or related components.

P0402 quick overview

Meaning	P0402: EGR Excessive Flow.
Is it serious?	Yes, this code signifies that the engine’s emission controls are not working properly, which can lead to reduced engine performance, poor fuel economy, and increased emissions.
Possible causes	– Malfunctioning EGR valve. – Blocked/clogged EGR cooler. – Faulty Mass Airflow (MAF) sensor. – Blocked or damaged corrugated EGR line. – Excessive carbon build-up in the intake manifold. – Clogged or malfunctioning catalytic converter. – Faulty vacuum transducer controlling the EGR valve. – Vacuum leaks or damaged vacuum lines.
How to diagnose?	Scan and Document: Use a diagnostic tool to confirm the P0402 code and check for other related fault codes. Visual Inspection: Examine the EGR valve, vacuum lines, and related components for any visible damage or disconnections. Test the EGR Valve: Disconnect the vacuum line from the EGR valve and see if the code still appears. If it does, the EGR valve might be stuck open. Examine the EGR Cooler: Check for clogs or blockages in the EGR cooler, which can lead to excessive flow. Check the MAF Sensor: Use a scan tool to analyze the MAF sensor data. Compare the values with manufacturer specifications. Inspect the Intake Manifold: Remove and inspect the intake manifold for excessive carbon build-up which can restrict the flow. Analyze Vacuum Transducer and Lines: Test the vacuum transducer that controls the EGR valve. Ensure all vacuum lines are intact and properly connected. Examine the Catalytic Converter: Check for potential blockages or restrictions in the catalytic converter which can cause excessive back pressure. Reset and Test Drive: After addressing any issues, clear the fault code, and test drive the vehicle to see if the code reappears.
What is EGR?	The EGR system redirects a portion of the engine’s exhaust gases back into the engine’s combustion chambers. Introducing these exhaust gases into the combustion chamber reduces peak combustion temperatures, which in turn reduces the formation of NOx.

How to fix P0402 – learn from mechanics

I looked into P0402 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: Nissan

Vehicle Information:
2002 Nissan Frontier 2.4L

Issue + Repair History:

• Symptoms: Poor fuel economy, loss of power, MIL lamp on. Fuel mileage dropped from 26-27 mpg to 22-23 mpg.
• Code: P0402 (EGR excessive flow detected).
• Previous repair: EGR valve replaced.

Suggestions from the Community:

• Clean out carbon from the EGR ports by removing the 4 hex plugs from the top of the intake manifold.
• Consider the possibility of a leaking injector causing a misfire and increased fuel consumption.
• Check if the EGR valve port might be clogged and if the engine has access plugs in the intake manifold.
• Inspect for a vacuum leak and use a smoke machine for easier leak detection.

Final Fix:
The EGR ports in the intake manifold were found to be plugged, especially port #4. Cleaning the ports through the plugs in the intake resolved the issue.

Case #2: Toyota

Vehicle Information:
1998 Toyota Tacoma DLX 2.4L

Issue + Repair History:

• Symptoms: Hesitation, MIL lamp on. The vehicle failed the CA smog test due to the check engine light.
• Code: P0402 (EGR excessive flow detected).
• Previous repair: None.

Suggestions from the Community:

• Check the VSV (Vacuum Switching Valve) for EGR, a common issue on similar models.
• Inspect the vacuum switching valve for the EGR, located at the right rear of the engine above and behind the axle.
• Examine the EGR modulator and solenoid; if faulty, replace them and ensure the EGR pipes are clean and have good flow.
• Test the EGR VSV with a vacuum gauge to determine if it’s faulty and opening or staying open during drives.
• Since P0402 is detected at idle, check for a noticeable misfire at idle if the EGR is open. Also, review the temp sensor connection and its wiring to the ECU.

Final Fix:
After testing the system and checking the wiring to the ECM, a signal was found up to the connector at the ECM but not at the pin. Replacing the engine wiring harness fixed the problem.

Case #3: Mazda

Vehicle Information:
1999 Mazda Miata, 10th Anniversary, 1.8L

Issue + Repair History:

• Issue: Excessive emissions and MIL lamp on.
• Code: P0402 (EGR excessive gas flow).
• Previous repairs: Replaced EGR, flushed port, replaced boost sensor and solenoid, installed new vacuum hoses, checked for vacuum leaks (reading was 19 inches), cleaned entire intake, installed new gaskets, checked all wiring for shorts.

Suggestions from the Community:

• Inspect for cracks in the surge tank, which may cause a P0402 code due to excessive gas flow.
• Check for an exhaust system leak.
• Ensure the solenoid airflow operates correctly.
• Clean carbon from the EGR outlet port inside the intake manifold to prevent the stored DTC P0402.
• Ensure the intake manifold’s EGR ports are not blocked, which could cause all EGR to flow out of the unblocked ports.
• Double-check ports behind the throttle body for blockages and clear them.
• Check the EGR system, particularly the bleed hole in the EGR valve. If plugged, it could allow excessive EGR, and the valve may need replacement.

Final Fix:
After extensive testing and consultation, the fuel surge tank was replaced with a new one. A hairline crack was found inside the surge tank using a bore scope, which was determined to be the root cause of the problem.

Case #4: Ford

Vehicle Information:
1999 Ford Taurus SE, 3.0L, 6 cyl, Gas

Issue + Repair History:

• Symptoms: Poor idle quality, hesitation, MIL lamp on.
• Code: P0402 (EGR excessive flow).
• Initial observations: Running rough, idling rough. EGR valve very hot without vacuum but cooled down after some engine run. The linkage connecting the induction butterflies near the throttle chamber was unhooked at one end.

Suggestions from the Community:

• Check if the EGR valve pintle is stuck open.
• Consider that the DPFE or EGR sensor could be more common issues than a defective EGR valve.
• The IAC valve could be causing the idle problem.
• Perform vacuum testing of the EGR valve; if it doesn’t affect the engine, clean the EGR valve and throttle body passages for carbon deposits.
• Check the EVR solenoid and its filter, as a clogged filter can create EGR flow issues.
• Investigate any reason the PCM might be commanding flow at idle.
• The DPFE sensor, especially aluminum ones, might be causing the P0402 code if there’s no vacuum to the EGR at idle.
• Consider an IMRC issue, such as stuck butterflies, which can cause rough idle and hesitation.

Final Fix:
The EGR valve and sensor were replaced to resolve the problem.

Case #5: Volkswagen

Vehicle Information:
2001 Volkswagen Beetle GLS, 1.9L

Issue + Repair History:

• Symptom: MIL lamp on with a recurring P0402 (EGR excessive flow) code after one normal drive cycle. The code appears even with vacuum to the EGR valve disconnected.
• Related Repair History: Replaced EGR valve with a new OEM unit, removed and cleaned the intake manifold, replaced MAF sensor with a new OEM unit.

Suggestions from the Community:

• The ECU calculates the flow of the AFM against EGR and detects any imbalance based on coding from the ECU references.
• If the EGR isn’t flowing, the ECU should not notice a deviation from the AFM airflow measurement.
• Disconnecting the EGR or coding it below threshold will trip the code.
• A blocked EGR, lack of vacuum, or a faulty AFM can lead to this issue.
• High and low boost pressure might sometimes set the EGR code, even if overboost protection isn’t triggered.
• The EGR cooler and corrugated line can either split/leak or get blocked.
• It’s suggested to reset basic settings if possible, especially since both the EGR and MAF have been addressed.
• The MAF sensor determines EGR flow as it detects air pressure. The catalytic converter might need checking for potential restriction causing excessive back pressure.

Final Fix:
The EGR cooler was found to be completely clogged. After addressing the clog, the issue was resolved, although the technician remained unsure of how a blocked cooler could set an excessive flow code.