Multiple Electrical Issues

🚗 2007 Honda Odyssey

• Customer said that multiple electrical systems stopped working all at once:
  • Turn signals, wipers, sliding doors, door locks, remote control, etc.
• No history of any damage, or repairs have been provided.

🩺 Diagnosis

Even before diagnosing anything, my first thought was that the MICU (part of the under-dash fuse box) has failed, which is a very common issue on these vehicles. So I, being statistically confident and lazy, just replaced the MICU with an easily available used unit, which didn’t fix the problem.

Eating my humble pie, I started diagnostics.

Found these codes in MICU 

• B1005: MICU lost communication with relay control module.
• B1006: MICU lost communication with door multiplex control unit (door lock switch message).
• B1007: MICU lost communication with combination switch control unit (headlight switch message).
• B1008: MICU lost communication with gauge control module (A/T message).
• B1012: MICU lost communication with MICU- rear junction box (RJU message).

Looks like a communication issues occurring on a single wire B-CAN bus.

Here is a diagram:

Main possible causes for these codes are

1. a shorted/open B-CAN wire, or
2.  an issue with one of the B-CAN connected ECU’s (power, ground, shorted wiring, internal failure) that pulls the whole bus off.

As can be seen on a diagram above, B-CAN bus connects up to 11 modules together (all over the car), which means that any one of them or wiring that connects them can disrupt bus communication, causing all these issues. It potentially can take many diagnostics hours to get to the bottom of it.

Next, I decided to verify that the B-CAN Bus is not operating.

• The easiest point of testing for me was the Master Switch on a driver’s door.
• B-CAN bus wire (Green/Red) measured a constant 12V  with ignition ON.
  • A good B-CAN communication will measure between 0V-12V.
  • A constant 12V confirms that the bus is off. Something pulls it “high”, shorting it to 12V.

So, time to start disconnecting one module at a time ( which is on a B-CAN bus).

• After disconnecting the rear fuse box, B-CAN bus came back to life, and most of the problems were solved.
• Digging deeper, I found out that it was enough to disconnect a G4 connector from the rear Fuse Box to have everything start operate properly. Everything except the left sliding door.
• Suspecting the issues with the sliding door, I disconnected the connectors that connected left front sliding door to the body of the car, which didn’t change anything.

At this point I found TSB 08-078

• TSB 08-078 | 2007 Honda Odyssey
• Turns out, that there is a connector C701 which has a B-CAN bus wire in between left sliding door and the rear fuse box.
• TSB pointed out that it could be corroded.
• Few minutes later I confirmed this to be the case.
  • B-CAN bus wire was shorted with a 12V positive wire through an oxidized path.
  • 

Cleaning connector C701 with a CorrosionX or Stabilant 22, and rewiring few badly corroded terminals, fixed all the issues at once.