CAT 257B Track Skid Loader Interlock Issues!

[gm@diezel]

Hello,

I have a CAT 257B Track Skid Steer that seems to be having interlock issues. Here is what the machine is doing. Both seat belt and park brake lights are flashing constantly and the machine with not attempt to crank or operate. I have read some about the solenoids but havent been able to locate them for sure or find any good wiring diagrams. Any information or help would be greatly appreciated!

Thanks

 

[Nige]

Have you checked both the seat bar switch and door switch (if fitted - or the bypass harness for said switch if the machine has an open cab) for correct operation.?

If you want a correct electrical schematic for your specific machine a Serial Number is always a good starting point.

 

[gm@diezel]

What is a good way to check the seat bar switch? I also have not checked the door switch.

Serial #SLK06521.

 

[Nige]

What is a good way to check the seat bar switch? I also have not checked the door switch.

A continuity check with a DMM is the usual way of doing it.
I'll look up the relevant schematic and post it.

 

[heymccall]

I can still start mine with the door open, and my switch works.
Double check for debris under the seat first.
Only the door and seat bar switch are part of the start interlock.
The door switch only prevents pilot enable.

 

[gm@diezel]

So I cannot get any continuity on the seat bar switch. I would like to jumper the wires and see if it works. There are three wires going to the switch and I am wondering which ones do I jumper together?

 

[Nige]

Check your PM's. I just sent you the schematic.

The armrest switch & seat switch (if fitted) work on an "either/or" system, connected to the ECM via G984 Pink and G985 Purple. One of those wires must be open circuit with respect to ground while at the same time the other one has to have continuity to ground (via 202 Black).
So check with your DMM between G984 & G985 and 202 Black. if you move the armrest to the other position whatever had continuity before should be open circuit and whatever was open circuit should have continuity.

Note regarding the seat switch: If your machine does not have one you should find wire G985 Purple connected direct to Pin 3 on the 4-pin connector instead of G983 Green that loops from the seat switch

 

[Nige]

I can still start mine with the door open, and my switch works.
Double check for debris under the seat first.
Only the door and seat bar switch are part of the start interlock.
The door switch only prevents pilot enable.

Good points.

 

[gm@diezel]

So when I check continuity at the plug at the ECM I don't get any continuity at any of the two wires with the armrest up or down. So I jumped G984 and 202 and got continuity down at the ECM but the machine still will not crank. Am I doing it wrong?

 

[Nige]

The illustration above shows the switch in the "Safety Bar Up" (Safe) position.
Try jumpering G985 and 202 Black.

 

[gm@diezel]

Hey we're on to something now! Jumpered G985 and 202 and now it starts! But I still have both flashing lights. If I have a bad seat bar switch could that be making the lights flash?

 

[gm@diezel]

Got my new armrest switch and installed it. Machine now starts as it should so that took care of that problem. But unfortunately I still have both park brake and seat belt lights flashing. So I'm going to check all solenoids and wiring going to them and see what I come up with. Any more suggestions as to what I should do?

 

[Nige]

When you check solenoids measure the resistance and compare it to spec. There is a table somewhere on the schematic with all the values.

 

[gm@diezel]

So I finally have figured out all my problems. The no start issue was the bad lap bar sensor. The interlock issue was the work tool detent coil which is located under the boot of the right hand joystick. Apparently it was shorted out. Unplugged that and all my problems went away! Got a new one coming. Thanks for the help!