I have a 2004 TL. Replaced battery a couple of months ago. While driving the car it went dead (no engine, no lights, no turn signals, no flashers, no power door locks). After sitting for 5-10 minutes, lights and flashers came back on. Car started and drove fine for a couple of days. I took battery back to have it tested and even replaced with another new one. Then one night I went to drive the car home from work and the key FOB would not open the doors. After getting in and starting the car several other problems were present: The dash light dimmer would not work, the turn signals would not work, parking lights would not work (lights would only come on when headlights were full on), power door locks would not work, windshield wipers would only work on fastest speed, A/C compressor would not work. On Nov 2 I had the car towed to my mechanic who said it could be the Multiplex Integrated Control Unit (MICU), but was only about 75% sure that could fix the problem, and that he might have to also replace the Relay Control Module. The car worked fine for about 3 weeks and then the same identical problems came back. I took the car back and mechanic replaced the RCM. When I picked up the car, he said that all the problems were fixed except that now the VSA switch light was on. He said to see if the other problems would stay fixed and then he would repair the VSA switch. Yesterday, all the original problems returned, with the addition of the alarm coming on when opening the door with the doors unlocked. I've spent over $1200 on this problem and nothing is fixed. I'm open to any suggestions. Thanks.

 

Recondition all the battery terminals/cables/grounds to all the wire harnesses under the hood and in the cabin-particularly around the dash area.

See if theres any improvement.

If no improvement I would replace the ecm.

You might want to check the ecm for waterlogged.

Use ecm is fairly inexpensive but will need to recode the imobilizer with all your keyes at the dealership.

 

I know this problem.

It's the MICU.
I read extensively through threads to help my friend out with the same symptoms.

Something common was that there was heavy rain in all the threads, and same thing too for my buddy.

 

We've already replaced the MICU, but problem has come back.

 

Does it appear to be rainy and humid out when this problem occurs?

Reason why is you may have a leak in your windshield and water can make its way down into the MICU.

 

I ran into the same exact troubles a few years back after replacing my windshield.
Check along the driver side of your windshield if you see any water spots along the A pillar.

One thing I figured out that would stop the alarm from going off unnecessarily was to leave me seat belt (drivers side ) buckled even when not in the car.

I even bought a replacement MICU but never used it. I put a fan on my floor board after having the shop reseal my windshield to dry things off.

Never encountered that problem again.

What gave it away was one night I was driving through a rain storm and my wipers started to change speed on its own and my dash lights would brighten and dim.

 

This is freaking awesome, guys. Perfect timing. I recently had my windshield replaced and have been battling a leak issue. Guy told me to bring it back whenever I can. Just last night while my wife was driving the car in HEAVY rain, the HFL (which stopped working years ago anyway) was stuck on and the battery light came on which makes no sense since I replaced it last week. When I got into the car this morning, the A pillar was moist to the touch and the cabin had that damp smell. I'm getting the windshield re-installed tomorrow. I'll do the floor board fan afterwards.

Sorry to hear that you've already thrown money at this and it's still occurring but glad I'm not the only one going through it. Good luck with it.

 

Usually when the battery light comes on during driving through heavy rain is that the accessory belt slipped when getting wet. Did you experience heavy steering?

 

I have been experiencing heavy steering in wet conditions or when it's cold outside. Been studying the DIY in the Power Steering Pump thread thinking this might be the issue. I'm an 08.

 

Thanks to all. Once my car dried out it started and ran normal again. I will see if I can find a good windshield repair company to remove and re-install. Also I found something else that may have contributed to a possible leak. A previous owner had a satellite radio antenna installed which is located on the front side of the roof right by the center top of the windshield. The wire runs along the drivers side of the windshield and down through the door. I will have that removed when the windshield is reinstalled.

 

Ok windshield has been replaced and car has been through several rains and all seems well so far. We'll see...