M5-111 DTC engine U02A3 error ACU

[Bucketload]

Hi All,

My first time posting so be patient with my silliness, thanks. A buddy of mine purchased this M5-111 with 480hrs on it. At 509hrs it through this code and went into limp mode. He then played with the buttons and found out if you pushed the constant rpm control, it allowed him to have full control of the rpm again. Basically out of limp mode. He then continued to run the tractor 2.5hrs. Thats when he called me. This is what I found. DEF tank is almost full but no indication of level on the dash DEF gage. DEF tank header unit looks fine and wire harness was connected. This code stated something about ACU communication buss error open. Has anyone run into this problem before and fixed it. I was able to get a download service manual for it and have been studying it nightly.

 

[tractorchad89]

Hello did you ever get this resolved I'm working on a tractor for a customer and it is doing the exact same thing.

 

[GreensvilleJay]

'comm buss open error' sounds like 'plug on cable has detached or mouse has shewed though a wire' to not allow the Auxillary Control Unit to talk to the Main Computer....

 

[whitetiger]

During operation, the aftertreatment system may intermittently become disabled, PM level raise, and multiple DTC codes are present.
With intermittent issues, poor electrical connections or contacts are commonly the cause of the issue. One area to check first is the CRS (main), CRS 2, and ACU relays located under the hood in the engine compartment. In addition to regular relay testing, inspect the relays for corrosion, moisture, damage, or other foreign material that could lead to high resistance between the relay contacts and the connector. Secondly inspect the J/C connectors located directly behind and between the ECU and the ACU.

Note: The ACU relay is also referred to as the comp relay (40A) in the wiring schematic or the compressor relay on page 10-138 of the workshop manual.

 

[tractorchad89]

'comm buss open error' sounds like 'plug on cable has detached or mouse has shewed though a wire' to not allow the Auxillary Control Unit to talk to the Main Computer....

Yea I looked at all that we ended up taking it to the dealer I believe the ACU itself is out thanks for comment.

 

[tractorchad89]

During operation, the aftertreatment system may intermittently become disabled, PM level raise, and multiple DTC codes are present.
With intermittent issues, poor electrical connections or contacts are commonly the cause of the issue. One area to check first is the CRS (main), CRS 2, and ACU relays located under the hood in the engine compartment. In addition to regular relay testing, inspect the relays for corrosion, moisture, damage, or other foreign material that could lead to high resistance between the relay contacts and the connector. Secondly inspect the J/C connectors located directly behind and between the ECU and the ACU.

Note: The ACU relay is also referred to as the comp relay (40A) in the wiring schematic or the compressor relay on page 10-138 of the workshop manual.
View attachment 157786

Yea I checked all of that and got a pin diagram from dealer. But without rest of manual it couldn't tell me a whole lot, it kind of pointed me to exact pins for ground and power from battery. And since those checked out and nothing was badly coroded or chewed up, I suggested customer take it to dealership so they can hook it up and see if it is bad. This is first system I have messed with that has the ACU, I worked at agco dealer for 10 years and Thier scr systems are all in one module they call the ecu. So hopefully come back from Holliday and get an answer

 

[tractorchad89]

During operation, the aftertreatment system may intermittently become disabled, PM level raise, and multiple DTC codes are present.
With intermittent issues, poor electrical connections or contacts are commonly the cause of the issue. One area to check first is the CRS (main), CRS 2, and ACU relays located under the hood in the engine compartment. In addition to regular relay testing, inspect the relays for corrosion, moisture, damage, or other foreign material that could lead to high resistance between the relay contacts and the connector. Secondly inspect the J/C connectors located directly behind and between the ECU and the ACU.

Note: The ACU relay is also referred to as the comp relay (40A) in the wiring schematic or the compressor relay on page 10-138 of the workshop manual.
View attachment 157786

Also you seem to have worked on more of these. This same tractor the digital display will show def empty after it runs for a min, it's like the dash resets and it will show full. Also the auto idle control will stay on the A or B option like you are trying to change what rpm you want the tractor to auto to, when button is pushed but it will not let you set,reset, or anything. You seen this before? I have checked connection and relays under dash.