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Code 402

I have a 1999 Explorer with 108000 miles. Last week it started pinging with a very low load. The fuel was low so I filled the tank, got on the freeway and headed home. As I exited the freeway I noticed the Check Engine light on. After some reading, I tried to clean the MAF sensor with liquid freon. I put it together, disconnected the battery, reattached the battery and powered up the engine. No more check engine or pinging. Two days latter the check engine light and ping came back. This time I disconnected the battery and tried more air and liquid freon on the MAF. Re attached the battery and no check engine for a few days. Yesterday the check engine came back. I went to Auto Zone and they said it had code 402 and I should check it out (not any help). What could it be and what should I look at?

TIA, Dave

Reply to
Davenandee
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P0402 = EGR flow detected at idle

There should not be any EGR flow at idle. I don't know how the PCM manages the engine when it detects this fault. In general, EGR flow reduces the combustion temperature, allowing ignition timing to advance without pinging, so there seems to be a connection between pinging and a malfunctioning EGR system.

The code could be set because there is flow at idle, or because the system detected flow, even though there isn't any. The list of possible causes for EGR flow when it should not exist is too long to repeat here. Some are: EGR valve stuck open, stuck EGR regulator solenoid, plugged solenoid vent or electrical shorts. Indication of flow when there isn't any could be due to misrouted, plugged, kinked or iced hoses or due to a bad DPFE sensor. If I had to make a bet instead of systematically troubleshooting, it would be on the latter, because of the age of the vehicle and the fact that these sensors are subjected to a harsh environment and don't last forever (mine failed at about 70000 miles). Nevertheless, I don't think that throwing parts at any problem is a good idea. The EGR system is not that complicated, and with the help of a decent manual and a few basic tools, troubleshooting is not such a big deal. A scanner will save poking through wires or back-probing, but is not essential. If this sounds daunting, my advice would be to check the two hoses leading to the DPFE, and if intact, to leave the rest to the professionals.

with a very low load. ....

out (not any help). What could it be and

Reply to
Happy Traveler

I'll agree with HT.... One down and dirty way to check for a leaking EGR valve is to start the motor from cold and feel the EGR valve (do NOT rev the motor... leave it idle).... If the EGR valve starts getting hot then it is either being commanded open or it is leaking internally.

Reply to
Jim Warman

Reply to
Captain Coleman

What is a DPFE sensor, what does it look like and where is it??

TIA, Dave

Reply to
Davenandee

Top part of the engine on the driver's side. Here's a picture:

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Reply to
Captain Coleman

Reply to
Captain Coleman

My '01 SportTrak went through this, and I ended up replacing both the DPFE and the EGR valve. Now before you start on me throwing parts at the engine, the EGR was so carboned up that it wouldn't move. I later cleaned it up with carb cleaner, but never reused it. With the new EGR, I still got the code, and then replaced the DPFE. That was an altogether different design, larger and installed backwards com- pared to the original. Codes went away, CEL light too.

Reply to
Martin F. O'Rourke

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