Volvo P2 water leaking into CEM

Problem description

The first years of facelift P2 models (V/XC70, S60, S80, XC90) - i.e. the entire MY 2005 and the first weeks of MY2006 - suffer from moisture or water entering the central CEM module. It is a manufacturing defect and it shows up quite often.

And - if it is not solved preventively - sooner or later it will catch up with every car from this series. The more the car sits or drives in the rain, the sooner the CEM module will die from corrosion. Even sooner if the drain channels in the area under the wipers get partially clogged.

According to a document published on the website of the US Department of Transportation (and probably also in various internal Volvo bulletins), this problem affects the following cars:

Structure week 200425-200545

Chassis numbers - the last 6 digits of the VIN:

Vehicle check

How to find out whether this problem has already been solved preventively on the car?

1. if it is in the listed range according to VIN
2. by looking through the grille under the joint of the left, driver-side wiper

If you see this "caterpillar" there, the wiring harness seal is still there from the factory. And you have a potential problem.
Warning: Cars with a higher chassis number, where the problem was already solved from the factory, look very similar (wavy caterpillar), but the problem is no longer there.

At this point you have 3 options:

A) Ignore the situation and just wait until water gets into the CEM. The car will then start doing all kinds of tricks, especially when wet. Later it will misbehave more and more, until one day the central brain stops working completely. Replacing it with a new one will make an astronomical hole in your wallet; replacing it with a used part is acceptable, but there is simply work and hassle involved.

B) Have this component replaced by a workshop you trust - RECOMMENDED, if your skills are not at least ***

C) Get into it yourself

Required parts and tools

This morning I chose option C). Encouraged by brief instructions from a colleague whose car had its first central unit heart attack a month ago, I jumped into it with enthusiasm. Most of the pictures are from him.

What you need:
• Plenum lid, P/N 30728860 - new cover
• Service grommet, P/N 30775689 - new caterpillar
• Cable tie, P/N P/N 983750 (2 required) - zip ties (ordinary cheap ones will also do)

Then just normal tools:
- Torx T25
- 8, 10, 12 and 13 mm wrenches
- puller (for the wipers)

Removal procedure

Procedure:
- disconnect the battery
- remove both wipers (ideally with a puller)
- remove the plastic cover under the wipers - it is enough to knock out the first four plastic "rivets"
- disconnect and remove the wiper mechanism (2x size 10 bolt)

You can uncover the cover (5 metal spring clips) and continue with 4 size 10 bolts and strip the whole original plastic cover. Cut it up with pliers (it will be recycled), and just as carefully cut open the old rubber caterpillar with a knife (watch out for the wires).

Then the 2 upper connectors on the CEM will appear = after disconnecting them, you may already see beginning corrosion, which is good to solve by refurbishing / replacing the CEM - for example at D5T5.com

Interior and CEM disconnection

At the top, in the corners of the CEM, there are still 2 Torx T25 screws - do not forget to unscrew them.

The original Volvo instructions apparently intentionally hide that the harness does not consist only of these two connectors, but that there are also several other wires going deep into the interior. This slightly changes the situation and also the complexity of the whole operation:

Now you need to move into the interior of the car, into the area under the steering wheel:
- remove the cover above the pedals with 2x Torx T25
- disconnect the small blue-grey connector on the bottom surface of the upper part of the CEM (almost invisible)
- then the long connector on the vertical part of the CEM and also the small connector with two thick red wires of the main power supply (there is a blue plastic lock and then another little safety clip against pulling it out).
- finally, there is still a pair of connectors clipped onto the side = disconnect them and unclip them from the CEM

- on the left side of the CEM there is a metal latch = after pulling it aside, the whole CEM can be tilted towards you and right after that it drops down out of the pins.

The above-mentioned harness branches out to several many other places:
- connector to the accelerator pedal unit (large grey one)
- brake pedal switch (small blue one)
- some kind of relay (black cube)
This part of the harness is fixed to the metal brackets by two plastic little clips (access is pretty bad, but eventually they will come loose)

Follow another thin harness - it heads down under the carpet (it is necessary to unscrew the hood opening lever - size 10 wrench), remove the plastic next to it and also the sill trim. Deep under the A-pillar, this harness ends with a connector - disconnect it.

The last - most annoying - part is the foot parking brake switch. There is no connector anywhere and the whole small switch is screwed onto the mechanism of the foot brake lever (but in such a way that you cannot reach the head of the screw). First unhook the Bowden cable that releases the brake = then loosen all three size 12 bolts (!) that hold the pedal mechanism to the body. It is awkward, but it can be done. At least it is not rusty here. Pull it out as far as the Bowden cables allow.
Finally, the small screw with a size 8 head is revealed and you can remove the foot brake switch.

If you have not forgotten anything, the whole harness can now be carefully pulled out of the car through the space under the wipers.

Replacing the caterpillar

Now the smaller diameter of the caterpillar, part no. 30775689 (diameter approx. 4cm), did not give much hope that this whole harness could be pulled through the caterpillar at all.

I chose this procedure:
- I removed the outer plastic and colored lever from all (3) colored connectors.
- first I pulled the largest connectors through the caterpillar - the brown one into the CEM, then the grey one from the throttle pedal, the relay cube, and then carefully, one by one, all the smaller ends and connectors of the harnesses. The caterpillar is made of quite flexible rubber, so in the end this task was easier than it first seemed.

Installation

The installation procedure is the reverse of removal.
- do not forget to also pull the harness through the cover, pull the harnesses through the opening into the interior
- screw the foot parking brake pedal switch back on and bolt the whole mechanism back in, fit the release Bowden cable
- connect the accelerator pedal connectors, the main brake switch and the relay, fix the harnesses back with the plastic holders (or with a zip tie if you removed them destructively)
- connect the harness under the carpet
- install the Bowden cable for the hood opening lever and click the plastics around it and the sill trim back in place

- install the CEM and connect all connectors (3 at the bottom plus the pair of connected connectors on the side, then the 2 connectors at the top).
- use a zip tie to secure the wiring as it was from the factory

- do not forget the 2 Torx screws at the top
- then place the harnesses so that they do not rub against sheet metal or any other sharp edge anywhere

- screw on the new cover using the four original size 10 bolts with rubber washers
- pull the caterpillar onto both ends and secure it perfectly with a zip tie.

Finishing up

Put the wiper mechanism back in (ideally lubricate everything with oil), then the cover, plastic rivets, the wipers themselves + caps.

Before finally covering the CEM, it is good to connect the battery and check whether everything works (except the wipers).

Pavel - ok2ucx

P.S. If the car is already doing strange "nonsense" or if you found corrosion in the connectors from above, it is time to have the unit professionally cleaned of salt and moisture before installation.
However, the CEM may already be in such an advanced stage that replacing it with another one will catch up with you anyway.