CAT D3G parking brake will not release

[dakotawest8]

I need some help with a CAT D3G dozer, serial #JMH01991. I have a blink code 124. I do not have CAT ET or schematics. I have found some stuff on the internet but not a lot.

The parking brake will not disengage.

On my 8v supply wire (pin 44 on the J1 ECM connector) it is grounded. I pulled the pin out of the ECM J1 connector and I’m getting 8v out of the ECM so I know the ECM is working properly. I have no voltage on the park brake solenoid. I’m not sure where else to go now. Would anyone be able to help?

 

[Nige]

Welcome to the forum and congratulations for getting much further along in the diagnosis than most.

As you have found Blink Code 124 relates to the 8v sensor supply. The only downside of using Blink Codes is that they don't tell you whether the issue is that it is shorted high or low. However you have unpinned the power wire at the ECM and found 8v then shorted low is the most obvious culprit. See attached.

The list of sensors powered by 8v is as follows:-
1. LH & RH track speed sensors.
2. Brake pedal position sensor.
3. Decel Pedal sensor.
Probably the quickest method is to unplug all four sensors then start reconnecting one at a time. My money is on one or other of the track speed sensors.

Also check your messages for an electrical schematic.

 

[dakotawest8]

Thank you @Nige. It was indeed the RH speed sensor. Full of oil…..

 

[CM1995]

Welcome to the Forums D8! Glad to have you.

You got one of our best Cat men right out of the gate. Glad you figured it out.

Just some friendly advice with the G series dozers - they are very finicky on voltage. If the system is not running a consistent 14.4 volts crazy things can happen like the machine slamming into park at full speed. Not fun.

Once it was a bad battery and the other an alternator going out.

Also they need to be calibrated with ET on occasion. Mine is on the trailer ready to go in as soon as I find time to take it. The track sensors get out of whack causing the machine to not track straight or go slower in forward and faster in reverse.

Bought a D5G new in 2004 and still have it. Great little dozers but they can be very temperamental.

 

[Nige]

Thank you @Nige. It was indeed the RH speed sensor. Full of oil…..

If your machine does not track exactly straight after fitting a new sensor on only one side you may have to invest in a recalibration of the hystat system.