Inifiniti G35 2003 :: Wet IPDM issue, how to fix it

Introduction to the wet IPDM issue

The Infiniti G35 is a technology filed car. as early as 2003 it already had a CAN bus and a few computers that take advantage of this network. This complexity comes with the cost of horrible situations when a failure of the CAN bus occurs. the problem described below affects the G35 after heavy rain fall. the I.ntelligent P.ower D.elivery M.odule cannot do it's job properly at that time and it affects the whole CAN bus. so all communication between the other computers in the car is not working. This kind of issue is really annoying on a luxury car and can lead to a loss of confidence in the car itself if not fixed.This situation occurred to me after a heavy rain, a quick search on the web revealed a few Youtube videos showing the trouble but no clear solution or understanding, people are stating that the trouble goes away by itself after a while. That is no answer for me, hopefully all those hours spent on understanding the G35 wiring diagram before buying the car was worth it!

Symptoms

 

*The video is not mine btw

the list of symptoms were noticed on a single drive home lasting about 35 minutes and totaling 50 km. the list is quite exhaustive and so was the situation. not the kind of crappy behavior you would expect from a luxury car.... 

WORKING SYSTEMS ( QUITE SHORT LIST INDEED ... )

• Engine ECU works fine
• Radio works fine
• ABS works fine
• Sunroof works fine
• door lock works fine
• SRS seems fine
• interior car lighting
• the only thing in the dashboard that works is the fuel level gauge, alternator warning light, ABS system is OK

NOT WORKING SYSTEMS( CHOOSE YOUR PICK THERE'S PLENTY FOR EVERYONE! )

All other gauges are not moving or being totally erratic.

• Tachometer
•  Speedometer
•  Engine temperature
• Check engine light flickers
• VDC light is on all the time
• SLIP light on all the time
• CAN bus communication is down or erratic across all systems,  

Additionally those systems are not working properly.

• -all systems relying on the CAN bus are in fail safe mode, some shut themselves down, some try to cope with the situation
• -dashboard clock stops working
• -VDC and traction control are OFF
• -Transmission ECU is in fail safe mode since the CAN bus is down, gear shifting is extremely harsh at all engine loads,
• -gear shifting is relative to car speed only
• -transmission will never down shift no matter how hard you step on the accelerator
• -manual gear shift mode is not working,
• -while cruising on the highway the transmission down shifts hard for no reasons on constant engine loads.
• -headlights are jumping from low to hi beam (people are thinking you want to tell them something ). you cannot engage hi beam yourself, it's like being epileptic.
• -electric radiator fan control, this one I can't confirm but it is sufficient to say this is quite critical as this is controlled by the IPDM and if the fans don't work when they should, you would get an overheating engine due to a bad CAN bus... what a lovely feature!!

Explanation 

( spoiler alert :: 2003 NISSAN ELECTRICAL ENGINEERS ARE DUMB ASSES!!)

Battery compartment without battery , IPDM and fuse box plastic cover

On older cars a 'gutter box' of some sort was draining the rain water coming to the bottom of the windshield and conveniently channeled it to the bottom of the car, it is called a cowl dash.on conventional design, only the wiper arms mechanism and wiper motor are installed there, end of the story. Nissan on the G35 decided they wanted to save weight and probably some money so they designed the car WITHOUT a cowl dash. Result:: when it rains, or you wash your beloved car, there is a waterfall running on the firewall inside the battery and Brake booster compartment. at the bottom of those boxes are holes meant to drain those boxes.

You can notice dirt marks around the top wiring harness, it indicates water flows there often then around the IPDM, this is a rust hazard to consider too..

First problem: the IPDM sits low cramped in the battery compartment adjacent to the firewall, there is always a humidity risk for this device since the water flow is in it's back, common sense suggest to never place critical electrical components in the way of water ...this is only common sense though...

IPDM with it's plastic cover, fender side fuse box out of the way

Second problem: the battery compartment is only equipped with one drain hole at the bottom and IT COMPLETELY CLOGS WITH THE YEARS! this lead to water accumulation in the bottom of your battery compartment, with sufficient water input it can get high enough to disturb your IPDM and voila You reproduced the problem on your otherwise pristine G35! (mine was completely clogged with mud and the water level was about 1/2" high.) looking down the battery compartment does not show much, you need to bend out of the way stuff and go there with your fingers to tell.

unclogged drain shown,IPDM out of the way, the drain is visible now

Third problem - the plastic battery tray gets filled with water under the battery and there is no drain holes in it.
( the blame goes to the cowl dash less design ) so you carry around about a glass or two of water that splashes here and there on hard accel/braking/cornering. Removing the battery tray and drilling holes at the bottom would drain that water accumulation when it fills.

The battery tray gets filled with stagnant water as the years are passing...

Fixing it 

tools needed to fix this

•  shop towels.
•  small air compressor equipped with a duster.
• something to unbolt 10 and 12mm nuts. (for baterry removal)
• narrow flat screw drivers can be useful to release the IPDM from it's bracket.

 things to do ( 15 to 30minutes )

1. Remove battery compartment plastic cover.
2. Remove the plastic part that meets with the lower part of the windshield.
3. take out your battery.
4. take out the water from the battery tray.
5. slide up the IPDM and fender fuse box, let the IPDM rest on the battery tray.
6. unplug the drain using fingers or better.
7. dry out as much as possible remaining droplets in the whole battery compartment with a towel.
8. reinstall IPDM and fuse boxes on their brackets.
9. remove IPDM and fuse boxes plastic covers.
10. using the duster generously dry all the wires connectors at the base of the IPDM. catch the escaping water with a towel using the other hand.
11. do the same thing in the fuse boxe.
12. do the same thing in the wiring harness behind battery tray and coming from under it.
13. install plastic covers on IPDM and fuses boxes.
14. Reinstall battery.
15. Start the car to confirm the problem went away.
16. Stop car, reinstall the lower windshield plastic cover.
17. Install battery compartment plastic cover.
18. Enjoy life.

Afterthoughts 

The IPDM is placed at what seems to me THE WORST PLACE EVER for a module as critical as it is.This module controls electrical power distribution across various systems and by placing it there endanger the CAN bus operation. I hope NISSAN was wise enough to improve on their electrical designs over the years...