D5G parking brake won’t release

[Dingbats0023]

Serial number

*MHK 12446*

*CATOOD5GPWGB02784*

I’ve read through several threads on this issue but I’m having some different problems.

Parking brake won’t release. Parking brake light stays on at all times regardless of position. Machine won’t start if switch is in released position, and backup alarm comes on but still won’t release. Hydrostatic ECM symbol stays on.

I have tested rocker switch with multimeter and it checks out. Tested alternator and batteries. Both read good and machine fires right up. I removed the big hydraulic filter to confirm nylon coupler is intact and oil spewed out as soon as machine started. Tested ohms on solenoids on pilot hydraulic valve and ohms test good. However I did not get any power supply at either plug going to solenoids. Is there a fuse or relay im missing that I should check?

 

[shopguy]

Welcome to the gang! Got any codes?

 

[Nige]

The first thing I would suggest is to get into the electronics and pull Diagnostic Codes. All it needs is a bent paperclip.

See the attachment. The critical illustration is the one at the bottom of Page 1.
When you have a list of Codes try erasing each one. The ones that cannot be erased are the Active Codes and are the ones in which you should be interested.

 

[pittsburgh cat man]

I think I would check for pump pressure

 

[Nige]

I think I would check for pump pressure

His comment regarding oil spewing out of the filter housing when the engine was cranked leads me to believe he has flow from the pump. Maybe not pressure but at least it indicates the coupling is not failed.

 

[pittsburgh cat man]

depends on if the hydraulic pump goes thru that filter too since it is driven off front of engine

 

[Dingbats0023]

After checking the fault codes it’s reading 254 and 252 service brake pedal and deceleration pedal. How would I go about checking both these sensors to confirm they’re bad? I wonder if I have a wiring harness problem

 

[pittsburgh cat man]

I think I would start by checking harness and plugs strange to have two sensors bad in same area

 

[Dingbats0023]

I removed the plate behind both pedals. Are the sensors accessible behind there? What’s the best way to test them ?

 

[Nige]

After checking the fault codes it’s reading 254 and 252 service brake pedal and deceleration pedal. How would I go about checking both these sensors to confirm they’re bad? I wonder if I have a wiring harness problem

Did you try erasing the Codes using the procedure I attached earlier.?

If you did and they would not erase, meaning they are both Active, then see the attached.
Check your message inbox for an electrical schematic.

 

[Dingbats0023]

I have tried to clear the fault codes I’m getting and cannot get decel pedal or service brake pedal code to clear. Following the diagnostic steps you sent me, I have low voltage at both sensors. Only 3 or 5 volts depending on which prongs I test. I also only have 1.4 volts of power at my pilot solenoids. Before I remove the connector on the ecu i wanted to confirm and make sure there are no relays I should test.

Also on the ecu is the larger plug j1?

 

[Nige]

I have tried to clear the fault codes I’m getting and cannot get decel pedal or service brake pedal code to clear. Following the diagnostic steps you sent me, I have low voltage at both sensors. Only 3 or 5 volts depending on which prongs I test.

The fact you can't get them to clear confirms that they are Active.

I'm a bit confused regarding the "only 3 or 5 volts depending on which prongs I test". The troubleshooting procedure requires the voltage to be tested between Pins A & B (blue and brown wires) with the sensor unplugged from the machine harness. What voltage are you getting under those circumstances.?

Try disconnecting both the sensors that are faulting from the machine harness and measure the voltage between Pins A and B.

Everything you are coming up with right now is indicating a wiring harness fault.

 

[Dingbats0023]

The first step in diagnostic says to test voltage between blue and brown wire. I’m getting 5 volts there. The second step is to test voltage between blue wire to ground. I’m getting 3 volts there.

The next step in diagnosis is to jump wires and test for resistance. Hopefully I get a clear answer there and confirm it’s wiring harness issue

 

[Nige]

The next step in diagnosis is to jump wires and test for resistance. Hopefully I get a clear answer there and confirm it’s wiring harness issue

The resistance test may or many not give you concrete results.
Try disconnecting the wiring at both the sensor and ECM end. Identify which ECM plug is which by relating the wire colours. Then connect one end of the wire to machine frame ground and hook a 5A fused test light to the other end of the wire. Any wire that will successfully pass 5A should be considered as good.

 

[Nige]

The first step in diagnostic says to test voltage between blue and brown wire. I’m getting 5 volts there. The second step is to test voltage between blue wire to ground. I’m getting 3 volts there.

The fact that in Step 1 you are only getting 5v where you should get 8v is an indication of a harness fault.

 

[Dingbats0023]

What type of diagnostic connector does this machine need? I have JalTest and I’m going to hookup and read the codes in depth. I know it’s not the regular deutsch 9 pin

 

[Nige]

I'm a bit baffled. You already know what the Codes are, you have the troubleshooting procedures, and your testing has shown that the supply voltage at the sensors is below specification. The only unknown is why although there are strong indications that it is a harness fault.
Whatever else you hook up in the way of electronic diagnostic tools is not going to tell you how to fix the problem.

 

[Dingbats0023]

Id like more confirmation then a Morse code symbol before I spend hundreds to thousands on a wiring harness. The machine has also thrown the 8 volt power supply code which really makes me want to verify before I purchase any parts

 

[Nige]

Why would you want to buy a harness when it could most likely be repaired.? Do you have any good automotive electricians close by..?

The 8v power supply code is related to the fact that the sensor power supply system voltage is low.

 

[Simon C]

I would suggest following Niges 5 amp test light trick to confirm that a particular wire is weak or degraded and then you can make a decision to run a wire if you find a bad one or buy the harness. Some of these wires can be replaced with another in loom quite easily. It is your money.
Simon C