DPFE Electrical Test/Diagram (?) p0402

[BuffaloXplorer]

DPFE Sensor or EGR Faulty? Help!

PLEASE READ!!!!! HELP!!


:fire: I've been stuck with a p0402 (EGR Excessive Flow) for quite some time, and have replaced every component within the last year (maybe 8 months). Each repair seems to eliminate the problem for a while, but then the CEL comes back. I'd reset the CEL, and it'd be off for a day, maybe two. Now, it's back before i reach my next destination. Something in the system is seriously wrong!

I think it's either extreme carbon buildup in the manifold pipe or a bad dpfe sensor (existing sensor is approx 8 months old).

According to Haynes, i can test the DPFE voltage to determine it's functionality. There are 3 wires in the harness: signal, ground and something, maybe power (?) and they're lined up top to bottom.

I'm not sure which is which, though, so i do not know which to test. Unlike other connectors (i.e. TPS), Haynes does not show which wires to connect to. It says to backprobe the harness when connected to the sensor, but with my straightpins i cannot get a consistent reading (they're thicker and i think they're not reaching the actual wires. I may try poking the wires with sewing needles and attaching alligator clips, b/c i need to work the throttle too.

The components involved in the EGR system are the Valve, DPFE sensor, EVR (vacuum regulator), manifold pipe, dpfe vacuum hoses and evr vacuum tubes. Is there anything that i am forgetting, or that could possibly cause this code?

 

[BuffaloXplorer]

From top to botton, i've got black/green, gray/red and brown/white - anyone know which wires would be ground, signal & reference?

 

[BuffaloXplorer]

Well, i figured out which is which and tested the sensor. According to the haynes manual, my sensor should read between .7v and 1.25 or so at cold idle, and raise to between 4.0-6.0v at normal operating temps. Mine started at 3.6v and stayed at that area. When vacuum was applied (by mouth, i'll have you) the sensor voltage ran up above 4.0 and then back down. I let it run for a while more and it dropped to around 2.5v at idle.

The readings indicate that there is flow when there should be none, but does this mean that the sensor is faulty or is it the valve?

I thought these readings would help me to find a culprit, and it's only confused me further. SHort of going to autozone and spending money on a new sensor,plugging it in and then testing the voltage again, i fear that i'll never solve the mystery of the EGR ghosts.

 

[ExplorerDMB]

Is the DPFE aluminum or is it made out of something else? If it is aluminium I would replace it. Ford had a huge problem with the DPFEs and a lot of vehicles end up with the same problem you are having because the heat from the exhaust and EGR system would get to the DPFE and just melt it basically. If it's not aluminum, I would look into the carbon build up. Good luck.

-Drew

 

[ExplorerDMB]

Hey, I found this on the internet:

It's possible the EGR valve itself is not closing completely. It's a little bit of work, but not too difficult to remove. Taking it out and doing a clean and inspection would be the best thing to do at this point.

REMOVAL:

Disconnect the vacuum hose from the Exhaust Gas Recirculation (EGR) valve.
Disconnect the electrical connector from the EGR valve sensor.
Remove the EGR valve nuts and the EGR valve.
Remove the EGR valve gasket and clean EGR gasket sealing surfaces.

INSTALLATION:
Position EGR valve with a new EGR valve gasket and install EGR valve nuts. Tighten to 15-22 lb ft.
Connect the electrical connector to the EGR valve sensor.
Connect the vacuum hose to the EGR valve.

EGR Valve - Explorer 5.0

Located at intake manifold

It's for a 5.0L Ford Explorer, but it's similar!

Hope that helps,
-Drew

 

[BuffaloXplorer]

Thanks DMB - i've got all that info. Yes, it is aluminum and i cannot find a plastic replacement. I cannot get the manifold tube off the exhaust so i can't clean it anyway.

Well, i purchased both a DPFE Sensor and an EGR Valve and replaced the sensor first. I figured if neither fixes the problem, i'd just return them as "new" to autozone.

When i ran the voltage test on the new sensor, it came up just over .6v, as a case study of EGR failure said it should. I found the article when i Googled "p0402" - i had read it almost 2 years before but it made no sense to me back then.

The Haynes manual (section 6-24(?)) says the voltage, when backprobed at the signal & ground terminals with engine on, should raise to 4-6v when finally warmed up, which was causing my dilemma - the voltage never raised at idle with either new or old sensor - it just stayed there at the initial reading (old sensor - 3.6v at cold/warm idle; new sensor .6v cold&warm idle) - no matter HOW warm the engine got (unless vacuum was initiated manually). I had both my new and old Vacuum Regulators handy, so i swapped them and got the same results. Both of the EVR units' resistance readings were fine, so i believe they're in correct working order and providing vacuum when necessary. Is the PCM faulty? Should the EGR be opening when the vehicle is finally warmed up - Because it's not! What could be causing the valve to do nothing at idle? Unfortunately, i don't have anything that can scan for DPFE voltage when driving (unless i can wire my tester to check while driving) - is this advised?

According to the case study, voltage at the sensor should only increase when vacuum was applied, which it did when i sucked on the plastic vaccum tube to the valve. Also, it never came close to the "4.0-6.0v" as mentioned in the Haynes manual - only reaching around 2.8v at "full suction" (think thick milkshake, thin straw).

With the original sensor readings of 3.6v+, it was telling me that the egr valve was almost fully open at all times. I know this was not the case, as i could hear the valve open and pop shut when messing with the vacuum regulator, so i'm confident that the valve is ok and the sensor was (once again) bad.

Who knows? I may be wasting my time and the CEL may be back tomorrow. Hopefully, it's not, but i will keep you all posted as to what happens, as i KNOW that this is a common problem, not always solved by a simple swap of the sensor.

 

[exploded99]

I'll take a shot here - hope this makes sense.

First, the DPFE sensor is there to report back to the computer that the EGR valve is opening and working like it should when the computer tells it to. In other words, the DPFE is there to tattle on the EGR valve if it does not open when the computer tells it to.
When the EGR valve is opened by the PCM (using the EVR) the DPFE senses how far it opens, and the voltage goes from 1 volt up to 5 volts, depending on how wide the EGR valve is open. The voltage goes back to the PCM, which checks it to make sure the EGR valve opened as far as it was supposed to.

Example: the PCM wants 50% EGR, so it uses the EVR to allow enough vacuum to go to the EGR valve to open it 50%. The DPFE senses the EGR is open and reports, say, 2.5 volts to the PCM which tells the PCM the EGR is open 50%. The PCM decides the EGR valve is responding like it should, and the world is wonderful.

If the DPFE voltage stayed at 1 volt (like at idle) the PCM would interpret that as: I told the D**n EGR to open 50%, and nothing happened (cause the voltage from the DPFE did not change), and would set an insufficient EGR code.

You had 3.6 volts at idle on your bad DPFE. Computer thinks: I did not tell the D**n EGR valve to do anything, but the EGR valve is opened cause the 3.6 volts coming from the DPFE tells me it's open. It will set an excessive EGR code cause it thinks the EGR valve opened when the PCM did not tell it to.

In reality, DPFE is lying to the PCM cause its bad, and all is fine.

You replaced your DPFE, which should fix your excessive EGR code. The computer will now see 1 volt at idle which will tell the computer the EGR valve is closed. The EGR valve is kept closed at idle by the PCM. If the EGR valve does open at idle (bad EGR valve, say) the exhaust gases will kill the engine usually.

NOW, if you get an INSUFFICIENT EGR code its going to be due to a clogged manifold pipe or because one of the two hoses going to the DPFE from the manifold pipe is plugged / fallen off.
In that case the DPFE could not tell the EGR valve had opened, and would send 1 volt to the PCM. PCM would get pissed cause it told the EGR valve to open, but the DPFE is telling the PCM the lazya**EGR valve is not doing anything (1 volt feedback) and would set an insufficient EGR code.

Prolly you are going to be ok.

 

[BuffaloXplorer]

Thanks Exploded - i'm pretty certain that i nabbed the culprit this time. Your explanation of the system is right on the money, and after reading & rereading the case study i referred to above (over and over and over again), as well as the haynes manual, i've pretty much become an EGR expert.

The one thing that HADme stumped is that the Haynes manual said that the DPFE voltage should raise when the engine warmed at idle, which it clearly should not. Also, stating that it should raise up to between 4-6v was incorrect as well, and i'm sure it has misled others in the past.

Thanks, all, for your help - not just with this thread but with all the other threads i've posted over the last 2 years in regards to my p0402 dilemma. Now, if i can fix my p-brake and get new treads, i will actually get a valid inspection sticker on my baby!!