Check engine light comes on indicates EGR flow what other parts of egr system can cause this code besides egr valve. I would hate to replace egr valve only to find out something else in system caused check light.

Hi Joe

Yes, it is EGR Valve. Did you clear the code?

https://www.google.com/search?q=1996+Toyota+Corolla+1.6++P0401

What about the IAC?

https://www.google.com/search?q=1996+toyota+corolla+1.6+iac+valve

What are the plugs like?

It is something simple.
..

cleanout egr valve and troutle body . Or replace egr with new one, clean, check vacumm lines , check for clogged check , depending on modle of car you can pippoint problem as some have a common part problem depeding with make of car. But all have to do with exaust system. Insufficient flow exaust flow. Im not an expert, all I know it is related to this, I have it myself so im googling it.

Ford EGR valve

The OBDII fault code P0401 means that the engine computer has detected that the Exhaust Gas Recirculation (EGR) system flow is insufficient. Read more how the EGR system works below. What could cause the code P0401 - clogged or restricted EGR passages
- faulty EGR valve
- EGR valve stuck closed
- problems with the DPFE sensor (Ford)
- problems with hoses to the DPFE sensor (Ford)
- problem with the EGR vacuum switching valve (Toyota)
- clogged catalytic converter
- carboned up EGR temperature sensor
- vacuum supply issues at the vacuum-operated EGR valve
- electrical problems with the EGR valve control circuit
- engine computer problems
helpful website helps you with pinpoint and sou;ution related to auto make and model shows you most common cause of code reading.
www.samarins.com

Here is a list of possible causes. Some things you have already done.

EGR solenoid valve harness is open or shorted
- EGR solenoid valve circuit poor electrical connection
- EGR volume control valve stuck closed
- Faulty EGR Pressure sensor
- Faulty EGR temperature sensor and circuit
- Faulty EGR Valve
- EGR passage clogged
- Exhaust gas leaks
Read more: http://engine-codes.com/p0401_ford.html#ixzz28fATCih2

depending on the year make and model of the vehicle, the most likely cause of this code is the DPFE sensor which controls EGR operation.

Are you reset the stored codes there? The EGR (Exhaust Gas Recirculation) valve controls an engine's emission of smog-causing nitrous oxides, or NOx. Its job is to route a portion of the exhaust gases back into the intake manifold. That lowers combustion temperature to below 2,500 degrees Fahrenheit - the temperature at which NOx gases form.

EGR flow is controlled by the engine's computer, which opens or closes the valve as needed. The EGR system is, for the most part, in the "out of sight, out of mind" category, and typical doesn't require regular maintenance. But if it gets clogged with carbon deposits, you'll see your "check engine" light come on, and a code (perhaps P0401 or P0402 or P0403) will show that there is insufficient flow. That typically results from a vehicle being driven persistently on short trips that don't allow the engine to fully warm up. Flow problems also can be caused by carbon buildup due to failure to change the oil frequently enough.

A clogged EGR valve not only results in higher emissions, it can affect fuel economy and cause rough idling - even serious engine damage. Valves can usually be cleaned, but replacement is often recommended.

About thie generic fault code, I suggtes check this description and tips for solution information: DTC-P0401-Tests (keep in midn that this code applied for alot brands, Hyundai included).

Keep us updated.

The EGR Valve and System - it's just three letters, but EGR can result in AGGravation.

Common in automobile emission systems since the early 1970s, the EGR (Exhaust Gas Recirculation) valve controls an engine's emission of smog-causing nitrous oxides, or NOx. Its job is to route a portion of the exhaust gases back into the intake manifold. That lowers combustion temperature to below 2,500 degrees Fahrenheit - the temperature at which NOx gases form.

EGR flow is controlled by the engine's computer, which opens or closes the valve as needed. The EGR system is, for the most part, in the "out of sight, out of mind" category, and typical doesn't require regular maintenance. But if it gets clogged with carbon deposits, you'll see your "check engine" light come on, and a code (perhaps P0401 or P0402 or P0403) will show that there is insufficient flow. That typically results from a vehicle being driven persistently on short trips that don't allow the engine to fully warm up. Flow problems also can be caused by carbon buildup due to failure to change the oil frequently enough.

A clogged EGR valve not only results in higher emissions, it can affect fuel economy and cause rough idling - even serious engine damage. Valves can usually be cleaned, but replacement is often recommended.

A code P0401 most likely means one or more of the following has happened:
* The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
* There is a blockage in the EGR (tube), most likely carbon buildup
* The EGR valve is faulty
* The EGR valve may not be opening due to a lack of vaccuum

Possible Solutions: In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.
* Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's & DPFE voltage. There should be a noticable difference in RPM's with the EGR open
* Clean out the EGR valve and/or tubing to remove deposits
* Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
* Replace the DPFE sensor (with a good quality / OEM one)
* Replace the EGR valve

possible but the code refers to the valve and or the solenoid to operate the valve
could be a loose / broken wire or bad ground connection
if it is that bad , replace the egr unit complete

Technical Description

Insufficient EGR Flow

What does that mean?

EGR stands for Exhaust Gas Recirculation. It is part of the vehicle emmissions system, and is used to reduce combustion temperature and pressure to control Oxides of Nitrogen. There are generally three parts to the EGR system: the EGR valve, an actuator solenoid, and a differential pressure sensor EGR (DPFE). These things work together to deliver the correct amount of recirculation based on engine temperature, load, etc. The P0401 code means that OBD detected an insufficient amount of EGR.


You may notice drivability problems such as pinging (a.k.a. pre-ignition knock) when the engine is under load or the vehicle is at higher speeds. There may also be other symptoms.
Causes

A code P0401 most likely means one or more of the following has happened:

* The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced
* There is a blockage in the EGR (tube), most likely carbon buildup
* The EGR valve is faulty
* The EGR valve may not be opening due to a lack of vaccuum

Possible Solutions

In fixing this code, it is quite common for people to just replace the EGR valve only to have the OBD code return. The EGR valve is not always the culprit.

* Use a vacuum pump and pull the EGR valve open while monitoring engine RPM's & DPFE voltage. There should be a noticable difference in RPM's with the EGR open
* Clean out the EGR valve and/or tubing to remove deposits
* Check the voltage at the DPFE, compare to specified values (refer to a repair manual for your specific model)
* Replace the DPFE sensor (with a good quality / OEM one)
* Replace the EGR valve

P0401 insufficient EGR flow.

Possible causes:

• Fault in vacuum supply to EGR vacuum regulator solenoid.
• EGR valve stuck closed or iced.
• EGR valve diaphragm leaks.
• EGR valve or flow path restricted.
• EGR vacuum hose off, plugged or leaks.
• VPWR circuit open to EGR Vacuum Regulator solenoid.
• EVR circuit to PCM open.
• EVR circuit to PCM shorted to PWR.
• Differential Pressure Feedback EGR (D.P.F. EGR) sensor pressure hoses both connected improperly.
• D.P.F. EGR sensor pressure hoses reversed.
• D.P.F. EGR sensor VREF circuit open.
• Downstream pressure hose off.
• Downstream pressure hose plugged.
• Damaged orifice tube assembly.
• Damaged EGR Vacuum Regulator solenoid.
• Damaged D.P.F. EGR sensor.
• Damaged PCM.

P0443 indicates an intermittent EVAP canister purge valve circuit failure.
Possible causes:

• Intermittent EVAP canister purge valve or VPWR circuit open.
• Damaged EVAP canister purge valve.

Insufficient EGR Flow Detected

Possible Causes:
DPFE sensor signal circuit is shorted to ground
DPFE sensor VREF circuit is open between sensor and PCM
DPFE sensor downstream hose off or plugged
DPFE sensor hoses both off, loose or damaged
DPFE sensor hoses connected wrong (reversed)
EGR orifice tube is damaged or restricted
PCM has failed
And what sets the code is…….Engine started, engine running in closed loop under steady cruise conditions, and the PCM detected the DPFE sensor input indicated insufficient EGR gas flow. Run the KOER Self-Test, and if DTC P1408 is present, the fault is currently present. This code sets in 2 Trip(s). The light will stay on until the cause is repaired. A bad EGR valve is only on possible cause.

Hope this helps,

Dave