john deere x300 ecu failure mid mowing?

[kevdynamite]

hey all. first post here, and i apologize if this has been beaten to death, but my x300 shut off and backfired on me while mowing today. from my research, the ecu modules on these tend to go bad, but is that something that may happen in the midst of use? i had a dead battery at the start of the season--about 3 months ago--but i was able to jump to get through that first mow and then replaced the battery for the next time i used it. just trying to avoid getting a $100 part that may not be the actual issue here. i put an OEM tune up kit into the mower about 2 months ago, so plugs, filters, oil is all new.

please advise, thanks!

 

[sgkent]

3 things are needed to make an engine run. Air to fuel, spark, and compression. Need to figure what is missing. The JD folks here will advise you to get the owners service guide from JD. Supposedly owners can get one by calling JD. Regardless, folks here will want to know the exact model number and serial number to answer questions more specific than what I have posted.

 

[Deleted member 97405]

The ECU you are referencing is actually called an interlock module. It contains your safety system. It is not an ECU (engine control unit), meaning it does not control the engine. All it does is ground the ignition coils if the safety system calls for it. SO....if you suspect an issue with it, find the black wire going into your engine harness and unplug it. This will remove the ground from your ignition coils. Keep in mind, you've just unplugged your safety system. SO....make sure your pto switch is off and your parking brake is set before cranking the engine. If the engine starts with that wire unplugged, suspect your module is bad. It is located up under the dash and secured with a single 10mm screw. Good luck!

If the above doesn't work, make sure you're getting fuel to the carburetor and that you're fuel solenoid on the bottom of the carb 'clicks' when you turn on the keyswitch.

 

[StarTech]

Interlock controls more than just the ignition coils.

Usually when these fail I do bypass surgery on them. There is currently four ZTRs here that had up to a triple bypass done the module.

 

[kevdynamite]

The ECU you are referencing is actually called an interlock module. It contains your safety system. It is not an ECU (engine control unit), meaning it does not control the engine. All it does is ground the ignition coils if the safety system calls for it. SO....if you suspect an issue with it, find the black wire going into your engine harness and unplug it. This will remove the ground from your ignition coils. Keep in mind, you've just unplugged your safety system. SO....make sure your pto switch is off and your parking brake is set before cranking the engine. If the engine starts with that wire unplugged, suspect your module is bad. It is located up under the dash and secured with a single 10mm screw. Good luck!

If the above doesn't work, make sure you're getting fuel to the carburetor and that you're fuel solenoid on the bottom of the carb 'clicks' when you turn on the keyswitch.

i don't notice the solenoid clicking when turning on the key, but when i removed it, the pin is freely moving and not stuck. i should have turned the key with the valve connected and removed from the carb, but i wasn't thinking at that moment. i'll have to dig more into it tomorrow and see what i find. appreciate all the responses here. i am an electrician by trade, but i've never done much work on my vehicles or power equip. always been afraid of making it worse!

 

[StarTech]

Check that there battery voltage across the fuel solenoid. If not then it is bypass time or a new interlock module. That was my first bypass I did on a Z830A interlock module,

 

[Deleted member 97405]

Interlock controls more than just the ignition coils.
View attachment 61471
Usually when these fail I do bypass surgery on them. There is currently four ZTRs here that had up to a triple bypass done the module.

Technically, you are right. As stated in my answer, the module contains the safety system. Thank you for backing me up on that. In the context I was referring to (ECU definition), this module only controls the ignition coils on the ENGINE. Therefore, it's not referenced as an ECU, as that would infer that it controls air/fuel ratio, ignition timing, etc. Not creating a fight here. Just clarifying for the customer so that if he goes to a dealership for the part, he knows what it's called so they can get the right part for him. Good luck!

 

[StarTech]

Technically, you are right. As stated in my answer, the module contains the safety system. Thank you for backing me up on that. In the context I was referring to (ECU definition), this module only controls the ignition coils on the ENGINE. Therefore, it's not referenced as an ECU, as that would infer that it controls air/fuel ratio, ignition timing, etc. Not creating a fight here. Just clarifying for the customer so that if he goes to a dealership for the part, he knows what it's called so they can get the right part for him. Good luck!

Sorry but that module also controls the anti-after fire fuel solenoid on the carburetor just to be clear here. That was my very first pass I did on a Z830A back in 2018. I have since done another Z830A, a Z925A, and a Z950R. With Z925A having the triple bypass surgery as the PTO, Fuel Solenoid, and Seat switch parts of the interlock all failed the same day.

The interlock pin out I posted is from the X300 service manual I got here.