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D6n parking brake won't release

Pushing forward

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Mar 13, 2023
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Location
Missouri
Prior to this, once or twice in the last 3 years brake light would be on upon start up and nothing would engage. When depressing the brake pedal it would reset. The day it happened, would be running and it would slowly come on then lock up. Shift the machine to neutral and it would reset. First time it did it, it reset and then ran for an hour without any problem. Then it happened again, reset and ran a half hour. Did this until would on releases for 5 minutes. Trying to finish a pond with severe storms on the way and 2 hours left to finish is why I kept going. Cat tech thought it was the parking brake, so that is the trail we followed.
 

Pushing forward

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Missouri
The brake pedal sensor has a pink G939, a blue 140 and a brown F790 going to the connector. Tag on this part of the harness reads BRAKE AJ_C28. When checking the duty cycle, it reads 99.9% and 100% when pedal is depressed.
 

Nige

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G..G..G..Granville.........!! Fetch your cloth.
99.9% up and 100% when depressed.
That ain't right. It should read close to zero with the pedal up.

You're going to have to do some disassembly. First remove the sensor (2 screws with nuts IIRC) making sure that you keep everything in the same position without turning it. You may have to disconnect it from the machine wiring harness first. There is a slot (arrowed) in the sensor that is driven by a pin on the pedal shaft.

When you get everything apart inspect for anything obviously broken, worn, or damaged.

Mark the position of the centre shaft of the sensor with respect to the body. Hook the sensor up to the machine wiring harness and with the key on use a flat screwdriver in the slot and rotate the shaft slightly in each direction and watch what happens to the % output signal. Report what you find.

1683566062339.png
1683566369552.png
 

Nige

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G..G..G..Granville.........!! Fetch your cloth.
While you are in that area you could also check the operation of the pedal position switch. The wires in the machine harness connected to it are 198 Red and G731 Grey.
Do not forget to test the operation of the brake pedal position switch (circled) while you are in that area. The switch contacts should be open until the brake pedal gets almost to the bottom of its travel. At that point they should close.

1683570968689.png
 

Pushing forward

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Same readings as previously. At one point was getting no readings. Found a blown fuse and replaced it. Same reading as before. Moved on to check brake pedal position switch. Removed the connector housing. When reconnecting the wires back, the gray went on smoothly. The red wire arced on the brake pedal and melted the tip a bit. The key switch was off, but master was on. Blew the same fuse as before number 16 the power train control fuse. With pedal depressed duty cycle reads 99.9%, at up position it reads 98.3%.
 

Nige

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28,976
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G..G..G..Granville.........!! Fetch your cloth.
Moved on to check brake pedal position switch.............. The key switch was off, but master was on.
The brake pedal switch power supply on 198 Red is permanent 24v from the battery. Makes no difference if the master switch is on or off. The only way to cut the power to that wire is disconnect the batteries. Apologies, I should have warned you.
The brake pedal switch is a simple continuity test, open or closed. What were the results.?

If the sensor % reading does not change when you rotate it with a screwdriver then it has failed and requires replacement. The Part Number is 214-4863.
 

Pushing forward

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Missouri
The continuity test showed it is working. I will order the other sensor and let you know results when it is installed.
 

Nige

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G..G..G..Granville.........!! Fetch your cloth.
I will order the other sensor and let you know results when it is installed.
Hold on a mo'. Don't get too previous...........

What I suggest is this. When you receive the new sensor as a first step hook it up to the machine wiring harness connector, put the key on, and make sure you are getting a varying signal from it when you rotate it with a screwdriver. Then set it to somewhere in the range between 0 and 5%, probably closer to 0% truth be told.

At this point, and assuming the pedal is all the way up, you should be able to slide the driving tab on the end of the shaft straight into the sensor. The two fixing screws ought to be lined up bang on and pretty much drop straight in. Once you have installed the sensor and tightened the hardware test the output % again first with pedal up and then with it depressed all the way.

It is very important that the % signal at each end of the pedal travel does not go below 0% with the pedal fully up nor above 100% with it fully pressed down. If the signal is outside this range the sensor might need to be calibrated (it may also generate a 113.0468.08 Active SERV CODE), and that procedure will require ET. I have my fingers crossed that it won't be necessary.
 
Last edited:

Pushing forward

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Ha, no pigeons involved. Been super busy, went to put on sensor today. The sensor isn't the right one, so will have to get this remedied. Is there any reason I shouldn't put the final drive back on the machine?
 
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