threw a cel code p0401 EGR insufficient flow error
threw a cel code p0401 EGR insufficient flow error
Hey guys, today out of nowhere I threw a cel code p0401 EGR insufficient flow error from my Evo, the scanner picked up this code twice. Anyone have any suggestions, ideas or similar experiences. This is like the first time I've ever thrown a CEL in my car and am a little scared, was told that the car would just run rich and get poor gas economy...
TECHNICAL DESCRIPTION
• When the EGR vacuum regulator solenoid valve switches from "OFF" to "ON" while the engine is running, EGR gas flows.
• The ECM checks how the EGR gas flow signal changes.
DTC SET CONDITIONS
Check Conditions
At least 20 seconds have passed since the last monitor was complete.
Engine coolant temperature is higher than 76°C (169°F).
Engine speed is at between 1,000 and 2,000 r/min.
Intake air temperature is higher than 0°C (32°F).
Barometric pressure is higher than 76 kPa (11 psi).
Vehicle speed is 1.5 km/h (0.9 mph) or more.
At least 90 seconds have passed since manifold differential pressure sensor output voltage fluctuated 1.5 volts or more.
The throttle valve is closed.
Volumetric efficiency is lower than 20 percent.
While fuel is being shut off.
The ECM monitors for this condition for 3 cycles of 2 seconds each during the drive cycle.
Judgement Criteria
• The intake manifold pressure fluctuation width is lower than 3.5 kPa (0.50 psi). When the EGR vacuum regulator solenoid valve is turned ON.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )
• EGR valve does not open.
• EGR control vacuum is too low.
• EGR vacuum regulator solenoid valve failed.
• Open or shorted EGR vacuum regulator solenoid valve circuit, or loose connector.
• Manifold differential pressure sensor failed.
• ECM failed.
• When the EGR vacuum regulator solenoid valve switches from "OFF" to "ON" while the engine is running, EGR gas flows.
• The ECM checks how the EGR gas flow signal changes.
DTC SET CONDITIONS
Check Conditions
At least 20 seconds have passed since the last monitor was complete.
Engine coolant temperature is higher than 76°C (169°F).
Engine speed is at between 1,000 and 2,000 r/min.
Intake air temperature is higher than 0°C (32°F).
Barometric pressure is higher than 76 kPa (11 psi).
Vehicle speed is 1.5 km/h (0.9 mph) or more.
At least 90 seconds have passed since manifold differential pressure sensor output voltage fluctuated 1.5 volts or more.
The throttle valve is closed.
Volumetric efficiency is lower than 20 percent.
While fuel is being shut off.
The ECM monitors for this condition for 3 cycles of 2 seconds each during the drive cycle.
Judgement Criteria
• The intake manifold pressure fluctuation width is lower than 3.5 kPa (0.50 psi). When the EGR vacuum regulator solenoid valve is turned ON.
TROUBLESHOOTING HINTS (The most likely causes for this code to be set are: )
• EGR valve does not open.
• EGR control vacuum is too low.
• EGR vacuum regulator solenoid valve failed.
• Open or shorted EGR vacuum regulator solenoid valve circuit, or loose connector.
• Manifold differential pressure sensor failed.
• ECM failed.
The egr vac hose had popped off somehow. Doug thank you for your input 
. How's the car going now that you moved away from the coast? Got anything new for it lately?
. How's the car going now that you moved away from the coast? Got anything new for it lately?
Last edited by mitsuorder; Feb 2, 2008 at 11:25 PM.
go behind the throttle body with your hand and drop down until you can feel a little saucer shaped object, the egr, and there should be a vacum line attached, the nipple that the line attaches to is pointed towards the passenger front tire. pm me if you can't find it.
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man I'll try but it's in a pretty tight spot, all I can say is to feel around back there when this car is cooled down, you can't miss it if you just drop your hand down directly behind the TB I'd say about 6 inches max and feel around for a little flying saucer shaped metal object roughly 2 to 2 1/2" around.
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Joined: Mar 2004
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its right under the hose coming off the intercooler, i indeed had a hose that came off i took some pics of where its located so you can feel around, there are two vacuum hoses attached to it once closest to the driver side fender and one around the sensor, just feel around the edge and you'll find the other nipple
EGR Valve from above the throttle body (silver item next to black hose)
Close up of EGR Valve
EGR Valve from above the throttle body (silver item next to black hose)
Close up of EGR Valve
Last edited by nastea1; Apr 24, 2004 at 03:03 PM.
i had to reset my ecu, code never came back, after I put the hose back on the car still ran like crap, tech friend said that this situation had put the car into the safest "safemode" possible, woke right up after ecu reset and felt even better after about 500 miles on it. good luck, oh and btw all of my plugs had fouled out when this happened so I threw in a new set of BPR9ES's, thing was running so pig rich with that vac hose off the egr my plugs just got plummled.
I love you guys. With out these forums I would been lost. today I had the PO401 I though it was because my high flow cat, nope. It was a loose hose right where the EGR is. I loved touching those nipples though 