DIY: Manifold Differential Pressure Sensor Diagnose/Repair

**galantebeige** · 02-04-2009, 09:31 PM

This post has been edited to include new information:

DISCLAIMER: Some mechanical knowledge is required to perform the following instructions/tutorial. I am not and cannot be responsible for any kind of damage to either you or your car. Do not attempt if you lack the necessary skills.

I think I solved this problem. So far the "Service engine soon" light did not come back. I do have some pointers I have gathered across the net below. I would appreciate some input here I I have missed something.

THIS IS FOR A GALANT 2000, I4. I don't know if it is the same for the I6.

I ended up changing the sensor. (Step 3 below.) I have added some pics at the end of this post. Next is the original text of this post before I had a good solution.

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Manifold Differential Pressure Sensor Diagnose/Repair

Code P1400 :
(For Mitsubishi this means)
Manifold Differential Pressure Sensor Circuit
Probable Causes
1. Open or short circuit condition
2. Poor electrical connection
3. MDP sensor failure

I also have read that this is not a critical code. The car car operate just fine for a long time if not until it dies ... :-)

It's supposed to be an emissions code. Basically what I understand is that the sensor will indicate to the EGR how much exhaust to return into the engine for burning? (need confirmation on this). This in order to reduce emissions.

Some people have reported this code firing when they get a boost (from the excessive voltage from the boost); and there is a way to circumvent that problem. I do not have any modifications, so I don't think I want to fool the sensor into not detecting excessive voltages. I want a functioning MDP sensor that will trip when needed (as designed).
http://www.club3g.com/forum/gt-gts/1...got-p1400.html

Some people have reported this code when they had a bad cap. (Gasoline cap I suppose). This needs confirmation also.

After trying different things to solve the problem, it is recommended to clear the error codes, with the following procedure (if you don't have a OBD-II scanner):

https://www.thegalantcenter.org/showthread.php?t=15545

if that does not work, just unplug the battery for at least an hour.

I would like to try a few steps, one at a time, after reading all the posts I could, everywhere, I have listed these:

1 Check tubing for cracks
it is suggested to spray carb cleaner on the vacuum lines (not sure how this works)

2 Just clean the sensor/and the harness, clean the little holes inside the harness.
Use a 8mm socket to release both bolts. pull sensor out, it sits inside a hole in the harness.
Clean sensor side and also clean inside the harness, in that hole.

It's been suggested spraying CRC cleaner to clean up the sensor
http://www.club3g.com/forum/problem-...re-sensor.html

Test sensor and PCM using a multimeter (don't know the details on this)

3 Replace sensor myself

may cost around $140

4 Dealer.... :-(

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My experience so far:

I checked the wires, tubing, I think they are ok

I took the sensor out of the harness, and found some oil in there... (?) a little bit. Cleaned that out. Found two tiny holes inside the circular hole where the sensor fits in. One seems to be open just fine, the other appears to be clogged or maybe it is supposed to be like that. If you insert a needle, it will go all the way in one, but will not go into the other one.

After replacing the sensor, the code came back after a few days.

The two screws are 8mm. They have to be tightened to 43 inch-lb (5N.m). The U type wire will keep the sensor and the connecting port together. It just slides in and out. It works by tension to do this. It is sitting under tension, so remove carefully or it can fly out.

Got another used sensor (Part Number MD305600). Replaced the defective one. So far the code is gone! It's been 12 days.

I will keep this updated.

HOW IT LOOKS LIKE:

CABLE WHERE IT WAS ATTACHED TO:

HOW IT LOOKS LIKE ATTACHED:
(Notice U wire location.)

HARNESS WHERE THE SENSOR CONNECTS INTO:
(Notice two holes.)

**fatal1** · 02-05-2009, 03:56 AM

there is a resistor fix as well...im not aware of it being here but the steps can be found on c3g and will come up if you search for p1400

**galantebeige** · 02-05-2009, 07:54 AM

fatal1: excuse my ignorance but what/where is c3g?

**qnz** · 02-05-2009, 09:53 AM

club3g.com

**galantebeige** · 02-05-2009, 10:55 AM

Added all info that I could find into my post from club3g.org
Unfortunately, not very specific either. Did get a few ideas there.

**galantebeige** · 02-15-2009, 08:19 PM

Well, this is what I learned so far, after just cleaning up all the parts I took apart, I put it all back together, and tried to reset/clear the code with the cruise control instructions above. That did not work, so I just unhooked the battery for a few hours. The code is gone now for a week and I hope it does not come back...

**galantebeige** · 04-08-2009, 12:16 PM

So far, things are working back to normal. I would appreciate some input, is this good enough? how do I make it a DIY?

I mean, when I started, I did not have a solution. Now, I think I have, so I updated this post.