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P0090 - Pressure regulator control circuit

Pcb is awesome!! Def the guy with links and pics! You can try to tape up the crank sensor wiring sheathing and see if that fixes it as long as the wires inside arent damaged. Also check the relay. Open the lid and it will show you which relay is which. If its burnt looking, corrosion on the plugs, or even the surrounding plastic looks melted that might be the issue.

I'm "guessing" by your video and your smoke/steam on the right side of the engine, it may be something failing inside the alternator like a bad diode and then screwing with the PCM that regulates the voltage out to other downstream engine operating components.

And/Or possibly a bad/intermittent electrical connection or corroded wire/ground.

I'd make sure your battery mating surfaces (posts/terminals/body ground points) are wire-brushed cleaned).
Sometimes the simplest things are overlooked and screw stuff up to other components.

At the very least you can glob some dielectric grease on it and plug it back in if it looks ok.

As far as electrical connections, I've recently learned you have to be careful using dielectric grease. It isn't conductive.

Dielectric Grease: What It Is and How To Use It

You have to have a good clean solid metal-to-metal contact with the connections as the dielectric grease will act as an insulator.

See snapshot from above link (click on photo to make it bigger and easier to read):
Caution - Using Dielectric Grease - Must Make Good Metal-to-Metal Contact First3.jpg


You might also read through some of the posts on this link below where some people had issues similar to yours.

Automotive Forums - Intermittent Issues
 
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pcb

The Diagram Dude
:
2002 MP5
I am replacing the fuel pump relay and the alternator soon,
I noticed either smoke or steam coming from that side of the car and the drive belt is worn a lot.

The alternator is quite easy to remove.

Screenshot_20210824-105143_Acrobat for Samsung.jpg


What the service manual fails to mention is that the alternator is trapped inside the engine bay once it's disconnected.

Most people remove all kinds of stuff from above and pull it out the top of the engine.

Mechanics usually pull the drive shift to get it out.

I remember one Mechanic figured out that if you remove the 3 bolts from the joint shaft, the shaft will move out of the way just enough to get the alternator out the bottom without removing the entire shaft and draining all your transmission oil/fluid.


20210824_104848.jpg
 

pcb

The Diagram Dude
:
2002 MP5
I'm "guessing" by your video and your smoke/steam on the right side of the engine, it may be something failing inside the alternator like a bad diode and then screwing with the PCM that regulates the voltage out to other downstream engine operating components.

And/Or possibly a bad/intermittent electrical connection or corroded wire/ground.

That makes sense.
Take a good look at your electrical connector and the harness going to your alternator.


Screenshot_20210824-111502_Acrobat for Samsung.jpg



If there is no connection or an intermittent connection between the alternator and the connector, the alternator effectively shuts off.

I'd make sure your battery mating surfaces (posts/terminals/body ground points) are wire-brushed cleaned).
Sometimes the simplest things are overlooked and screw stuff up to other components.



As far as electrical connections, I've recently learned you have to be careful using dielectric grease. It isn't conductive.

Dielectric Grease: What It Is and How To Use It

You have to have a good clean solid metal-to-metal contact with the connections as the dielectric grease will act as an insulator.


Yes.
The dielectric grease protects the contact from oxidization.
It also helps conduct and dissipate heat.

If it conducted electricity, it would short out your relay terminals.
 

pcb

The Diagram Dude
:
2002 MP5
Be careful when installing your new alternator/belt.

You don't want to overtighten the belt or you'll strain and wreck your alternator bearing.

If it's too loose, your belt will squeal.


20210824_114329.jpg
20210824_114400.jpg
20210824_114433.jpg




A good rule of thumb is to reach down to the measuring point and twist the belt.

If you can't twist the belt to stand up vertically, it's too tight.

If you can twist the belt upside-down, it's too loose.