Engine CAN bus issues; Starboard engine will only start with Port engine off


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So...I'm hoping someone can offer some help.

I was changing my fuel filters and ran both engines a little with the fuel pumps disconnected (per the service manual). After replacing the filters and firing the engines up to check for leaks, all kinds of alarms started going off.

The SmartCraft Vesselview wouldn't sporadically show the engine data.

After checking all connectors and resetting the PCM's (which didn't help), I did some further diagnostics.

(1) The Startboard engine starts and everything reads OK as long as the Port Engine is OFF
(2) The Port engine will start, but as soon as it is key'd ON, the Starboard engine's CAN bus seems to go down as all the SmartCraft data goes away.
(3) With the Port engine running, the Startboard engine will NOT start
(4) Trim controls function for Port engine....but not Starboard
(5) Starboard engine has 7 CAN related Fault codes Active (CAN X and P); One specific code is reading "CAN Fault: PCM Authentication Failed"

I have a TechMate Pro and scanned both engines. The Starboard has a number CAN Faults, Type 9 and CAN X. That tool only reads an SPN # that I can find for cross-reference anywhere online.

If anyone has any advice, I'd really appreciate it. I'm totally stuck. I guess the mobile mechanic will be getting a call on Monday.

Update: I found the CAN X terminator connector in the harness a the front of the starboard engine. Doing a resistance check on that circuit shows only 40 Ohms. Referencing the same circuit on the port engine (which seems to be functioning properly), that circuit is showing closer to 120 Ohms.

Knowing a little bit about CAN system function, if the resistance in the circuit is too close to Zero Ohms, the communication cannot properly function as there is too much noise if the circuit is close to ground.

Thanks!
 
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Just in case anyone comes across a similar issue. Here was the diagnostic procedure and findings:

(1) Found CAN-X connector at front of starboard engine near diagnostic connectors and measure Ohm resistance for CAN bus. With the blue termination resistor (120 Ohms), the measured resistance on the circuit showed only 40 Ohms. The circuit resistance should be 120 Ohms with the termination resistor disconnected as the CAN bus needs to be at 60 Ohms (two 120 Ohm resistors in parallel gives that 60 Ohms).
(2) Once the CAN resistance issue was determined, downstream wiring diagnosis was next. Unplugged 14-way connector at back of engine that has all the external CAN wiring for the rest of the boat outside of the engine. Disconnecting that connector showed the CAN-X resistance came up to 120 Ohms. That meant the wiring or resistance issue was external to the engine (this was good news to me).
(3) Looking at the wiring routing downstream, the first module I saw was the TVM (I didn't know what it was called at the time). This module is the Thrust Vectoring Module that controls the "drive by wire" steering for the starboard drive. This boat has the DTS system with joystick. Unplugging the TVM resulted in the CAN-X resistance properly coming up to 120 Ohms. I checked the port engine for reference and it did not show this same behavior.
(4) With the TVM unplugged, all CAN faults cleared and the starboard engine started and ran correctly.
(5) I swapped the port TVM onto the starboard circuit (just as a test, the boat CANNOT be run like this as the modules are set specifically for each drive) and all faults cleared and everything appeared OK.

New TVM part # needed to be acquired through Mercury marine. The TVM also needs to be configured using the Mercury G3 diagnostic tool. Further discussion with an experienced Tech indicated the TVM initialization and set-up can be done with the boat in the water (another person told me it had to be dry docked). Also, I was instructed to NOT try to drive the boat with only one TVM functioning as if steering is only allowed for one drive, that drive could contact the other and cause damage.

I hope this helps anyone else encountering this type of problem with engine CAN bus or TVM module failure. Once I get it fixed, I'll circle back and post my findings.
 
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