ECU

Can an ECU fail to send power back out on just one wire, but function normally otherwise?
Or when they fail do they just cease to function entirely?

 

Gona need more info here, what kind of issue are you having and what do you have?
In short yes but it's pretty rare.

 

JD X540 lawnmower. I have thrown it out on 3 lawnmower sites and don’t have an answer, but an ECU should function similarly on a mower, and I’ve always found this to be the most knowledgeable forum.

Everything tests good, and there seems to be no other issue other than power is not coming out of the ECU to the PTO. The PTO works when powered straight from the battery.

 

I can poke around later and see what I can find out about it but are you sure it isn't a safety switch preventing it from engaging? Lord knows they put enough safety interlocks on lawnmowers these days.

 

It has 3 switches. Seat, brake, and reverse. They all test for continuity and send a 12v signal back where they are supposed to.

 

I'll look into it tonight and see what I can come up with, you don't happen to have a wiring diagram or service manual I could look at do you?

 

This is a fuel injected engine? Pretty sure it is, but wanted to double check.

The PTO circuit is usually fed from its own relay and is completely separate from the ignition relay circuit and the starter cercuit relay.

Looking back at your post, the ECU should not be putting power to the PTO. The 7+amps inrush would play havock with the computer. The PTO gets it's power from the PTO switch and only powers up when all safety's are met.

Can you check your machine? There should be 3 relays.

Power to ECU
Power to start circuit
Power to PTO circuit

One thing that is often missed is the TVR (transient voltage resister) in the PTO cercuit. If it fails you can get some odd electrical issues.

They do share a common ground, so if there is a ground wire shorting to a power , you could have a back feed issue to another circuit.

EFI units are very picky about their voltage. If the rectifier is not putting out close to 14 volts, it won't run for beans.

Looking forward to more deets.

 

Are all the safety switches good?
The most common reason for the PTO to not engage is a bad safety switch.

As for a manual or schematic.
It’s Deere…..they will have any and all information pulled that’s posted online.
You are looking for manual TM2309. Just buy the manual. I finally did for my JD318.

 

It’s a Carbureted motor. 12v signal comes into the ECU from the PTO switch on grey wire 370b should come out on 502b blue wire which goes to the PTO but I can’t get any power on 502b.

 

That picture is really blurry.
I cannot make out much.

Any chance you can get a better picture?
Or a link to the picture?

 

Post in thread 'X540 ECU'
https://www.lawnmowerforum.com/threads/x540-ecu.73701/post-464928

 

I found you.
I have to create an account.
Let me do that and look at the diagram.

 

That is a safety module, I guess it could be called an ECU. It really only contains diodes and they do fail.

My Toro units have something similar and they go bad all the time.

 

Does this mower kill power to the PTO when in reverse?
It looks like it would. If so, see if you have power to the reverse wire at all times.
We need to eliminate all other variables before condemning the ECU / Interlock module.

 

It does kill power to the PTO when in reverse. There is a reverse override switch that will let the PTO remain on in reverse. I will test that out when I get home.

 

By reverse wire I mean 805B at the ECU

 

805B does not have power at the Ecu with the switch in either position

 

According to the diagram, the brake switch will NOT show power to the ECU if the Reverse switch is ON.
This might be the problem.
You are checking it with the key on, right?

 

Yes, key is on. The switch itself seems to be functional. It has power at the switch(yellow), also coming out of the switch(pink). It never makes it to the next harness connector.

I did verify the pink seat switch does have power at the ECU when depressed.

 

I was going to bypass the reverse switch anyway.