97 expedition EGR high flow error
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97 expedition EGR high flow error
Hope someone can help me on this one. From NY and need to get the truck inspected but can't due to the service engine light. Started with a low flow code and found a broken vacuum line and the EGR plugged at the intake. Fixed the problems and thought I was home free. No such luck... Now I have a high flow 402 error code. Checked the DPFE valve and EGR selonoid, both seem to be working properly. Don't have a clue on what to look for next. Anyone have any suggestions??? Trucks been running great for years and still runs great. Unfortuantely can't get the thing inspected until I get rid of the "service engine" light. Any insights would be greatly appreciated. Thanks...
Hotshot
Joined: Aug 2002
Posts: 12,679
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From: BC, Canada
Hi and welcome to the forum 
A P0402 means that PCM thinks the EGR is flowing at idle when it shouldn't be.
If it's actually flowing it will idle very rough and probably stall.
The common cause of a P0402 is a bad DPFE sensor.
A P0402 means that PCM thinks the EGR is flowing at idle when it shouldn't be.
If it's actually flowing it will idle very rough and probably stall.
The common cause of a P0402 is a bad DPFE sensor.
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Thanks for the welcome and the response.
I was poking around the dpfe sensor yesterday. I had it checked at auto zone and they told me it was OK. I didn't believe them. Their Technician's testing skills were suspect. He used bare allagator clips that kept shorting on each other and the can. I was appauled. Fortunately I looked over his sholder and got a good idea of what needed to be done.
When I got home I reinstalled the dpfe and used two multimeters to check the input and the output voltage. From what I was able to gain from my evesdropping was the reference voltage should be ~+5v. The output voltage should vary with engine speed;(or the pressure sensed within the DPFE itself). What I found was the input was close to the output voltage and there was little change with engine speed (+/-0.1v). It would make sense that I would get a high flow reading if the output from the dpfe was close to tthe input voltage at +5v.
Today I will go get a new one and hopefully my problem will be fixed although with the way my luck is running another code will pop up.
Thanks to all. I hope that this will also help others.
Inshock
I was poking around the dpfe sensor yesterday. I had it checked at auto zone and they told me it was OK. I didn't believe them. Their Technician's testing skills were suspect. He used bare allagator clips that kept shorting on each other and the can. I was appauled. Fortunately I looked over his sholder and got a good idea of what needed to be done.
When I got home I reinstalled the dpfe and used two multimeters to check the input and the output voltage. From what I was able to gain from my evesdropping was the reference voltage should be ~+5v. The output voltage should vary with engine speed;(or the pressure sensed within the DPFE itself). What I found was the input was close to the output voltage and there was little change with engine speed (+/-0.1v). It would make sense that I would get a high flow reading if the output from the dpfe was close to tthe input voltage at +5v.
Today I will go get a new one and hopefully my problem will be fixed although with the way my luck is running another code will pop up.
Thanks to all. I hope that this will also help others.
Inshock
Senior User
Joined: Mar 2005
Posts: 141
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From: Pullman Washington
What happens if you simply unplug your EGR electronics?? No feedback no foul?? Thats what happens with an EECIV & ODB1 ecm...You will get a CEL but no operational differances. Just a dead EGR sys...
Did I mention that I HATE EGR??? Crap design and expensive to maintain and a PITA to troublshoot.
Brad
Did I mention that I HATE EGR??? Crap design and expensive to maintain and a PITA to troublshoot.
Brad
Hotshot
Joined: Jan 2004
Posts: 19,762
Likes: 1,079
From: St Louis
Inshock,
That's really not a valid test. Figures, since it came from AutoZone. The EGR should not be flowing anyway except a highway speeds and then only when commanded to do so by the PCM. The sensor should measure the difference in pressure (vacuum) between the two ports. Therefore, the sensor output should not change unless there is flow through the EGR valve.
A new sensor has a very good chance of fixing it.
cuda, Can't do that if you have to pass emissions testing. Any CEl/SES and you fail.
Steve
That's really not a valid test. Figures, since it came from AutoZone. The EGR should not be flowing anyway except a highway speeds and then only when commanded to do so by the PCM. The sensor should measure the difference in pressure (vacuum) between the two ports. Therefore, the sensor output should not change unless there is flow through the EGR valve.
A new sensor has a very good chance of fixing it.
cuda, Can't do that if you have to pass emissions testing. Any CEl/SES and you fail.
Steve
Senior User
Joined: Mar 2005
Posts: 141
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From: Pullman Washington
Steve, Fair enough...I am aware it is an emissions system. My questions was if I were to unplug the sensor would it run virtually normal...Small loss of economy would possibly be about the worst result until the lad got a new sensor...Why the heck put up with a bad idle?? And if it does produce such a result and change the scenario then its a dead ringer that the sensor is bad...
Just askin' some questions...I am still learning the 5.4 obviously...heh
Thanks,
Brad
Just askin' some questions...I am still learning the 5.4 obviously...heh
Thanks,
Brad
