Cat 246C parking brake not releasing

[franm]

Hello

I'm currently trying to troubleshoot my Cat 246C (JAY01229). Does anyone have a document indicating the troubleshooting procedure for this exact model and serial number?
Specifically a troubleshooting manual that has this format.

https://www.justanswer.com/construction-and-road-equipment/iumhp-older-246-cat-driving-parking-brake-comes-put.html

Also, I'd also like to ask if anyone can provide an electrical schematic for this machine, with this format:
https://www.scribd.com/doc/25431069...-Track-Loader-Electrical-System-Schematic-pdf
(If this one is indeed the right one, let me know. However, from what I can read in it, it's not exactly for the JAY01229 version but rather the JAY2060-UP)

With these two documents corresponding to the same exact machine, I'd be able to troubleshoot properly and faster. The reason I asked is because the 201-BK wire from that help thread I linked is not in the schematic I linked. So there's either a typo from that technician or both documents don't belong to the same machine.

Thanks in advance.

 

[Nige]

I can send you an electrical schematic suitable for your Serial Number. Keep an eye on your message inbox.

Regarding a troubleshooting procedure can you describe exactly what is happening to the machine and what warning lights/alarms come on when you attempt to release the parking brake.

Being honest this really needs Cat ET diagnostic software hooked up to the machine to identify the Active Diagnostic Codes. With those Codes it is a reasonably straightforward procedure to do the troubleshooting.

There is an alternative to ET that might work, but it depends on the type of instrument panel in your machine. Post a photo of the panel in the upper RH corner of the cab please. Does it look like the image below.?

 

[franm]

Thanks for your reply

I'm not currently near my machine but found a photo of a panel that looks like mine.

It has only this panel at the top left.

The issue here is basically that when I press the switch, the parking brake light stays on, despite many attempts. Strangely, sometimes it turns off right away if I press the switch with the key in the ON position (before starting the engine), but it immediately activates again if I tilt the LH joystick to move forward (I can move the machine around left, right and reverse just fine, for some reason).

The bucket hydraulics safety will disengage properly and I can move the bucket perfectly fine. The seatbelt light also goes out when it's expected to.

I'm thinking it's got to be something wrong with:
a) The switch
b) The park brake solenoid not getting enough voltage or voltage at all

It could be something with the LH joystick too, I suppose. Why, in the rare event that I can get the parking break to disengage, does it re-engage only if I tilt the LH joystick forward?

Using an different joystick I had lying around, the parking brake will just never disengage, no matter what.

Sadly I don't have the resources to get ET or a technician atm, so I have to make do with what I got.

I might just need a quick and dirty solution, such as connecting the parking brake solenoid directly to 12V so that I can move the machine around in the meanwhile, but I don't know how to go about it.

 

[Nige]

I need to point out first that the link you sent regarding the park brake diagnostics is for a very early 246 machine which has an electronic system totally different to your 246C.

I sent you a copy of the correct electrical schematic. What I would suggest is to use that schematic and a multimeter to test the following: -

1. The operation of the park brake switch.
2. The wiring from the switch to the Machine ECM.
3. The wiring from the machine ECM to the park brake solenoid.
4. The resistance of the park brake solenoid coil.
5. Apply Batt+ to the park brake solenoid and check if you can hear the click as the valve spool moves.

You need to be aware that the park brake switch is an input to the Machine ECM and the signal voltage to the park brake solenoid valve is an output from that same ECM. There is no direct electrical connection between the park brake switch and the park brake solenoid.

It could be something with the LH joystick too, I suppose. Why, in the rare event that I can get the parking break to disengage, does it re-engage only if I tilt the LH joystick forward?

It could well be an issue with the PWM signals from position sensors of the LH joystick.
Does your multimeter measure duty cycle.? if it does you could measure the % duty cycle from the joystick fore/aft and left/right position sensors. If I recall correctly the duty cycle with the joystick in the centre (neutral) position should be 50% or very close to it.

 

[franm]

It could well be an issue with the PWM signals from position sensors of the LH joystick.
Does your multimeter measure duty cycle.? if it does you could measure the % duty cycle from the joystick fore/aft and left/right position sensors. If I recall correctly the duty cycle with the joystick in the centre (neutral) position should be 50% or very close to it.

Is there a troubleshooting step by step guide for a scenario where the joystick causes the park brake to re-engage? I've been searching for one that is similar to that I linked in my original post but to no avail.

I'll see if my multimeter has the duty cycle function, but would appreciate knowing if there are other measurements I can do in the meantime with a multimeter on the joystick and its wires (continuity, voltage, resistance).

Thanks for the tips and for the schematics!

 

[Nige]

Is there a troubleshooting step by step guide for a scenario where the joystick causes the park brake to re-engage?

No there is not. The electronic system on later machines such as yours use what are known as Diagnostic Codes for troubleshooting. If you have a certain DC then the troubleshooting for that Code will say "Test A B C D". That's why knowing what are the Active Code(s) is so important. Unfortunately the panel on your machine is the standard (not the optional) panel and does not have the in-built functions required to access the Codes.

If your meter does not have a duty cycle function then ask around and try to borrow one that does. It is the only way of measuring the signal output of the joystick PWM position sensors. The output signals are the important part.

Where in Argentina are you located.?

 

[franm]

Is there a procedure like the one below but for my machine? I'm not able to find the wire 202-BK on the schematic you sent me. What would the name or the function of that wire be, in case I can look it up that way? I don't wanna fry anything hah.

I'm assuming that the voltages and resistances listed here are the same for all 246C versions. It would be hugely helpful to write off either the solenoid or the joystick as a problem. This procedure seems to be aimed towards testing the solenoid valve, but as I said, can't find the wire 202-BK, or exact the wire harness pins.

Test Step 2. CHECK VOLTAGE AT THE SOLENOID VALVE WITH KEY SWITCH OFF

Turn the key start switch to the OFF position.

Locate the parking brake solenoid under the cab.

Disconnect the parking brake solenoid from the electrical connector.

Measure the voltage across the two contacts of the harness connector (A958-WH and 202-BK).
Expected Result:

The voltage should be less than 2 DCV.

Results:

• 
  OK - The voltage is less than 2 DCV. Proceed to Test Step 3.
  
  NOT OK - The voltage is greater than 2 DCV.
  Repair: The wire harness is shorted to a + battery circuit. Repair the wire harness or replace the wire harness.
  Stop.

Test Step 3. CHECK VOLTAGE AT THE SOLENOID VALVE WITH KEY SWITCH ON


Turn the key start switch to the ON position.

Measure the voltage across the two contacts of the harness connector (A958-WH and 202-BK).
Expected Result:

Voltage should be less than 2 DCV.

Results:

• 
  OK - The voltage is less than 2 DCV. Proceed to Test Step 4.
  
  NOT OK - The voltage is greater than 2 DCV. Proceed to Test Step 6.

Test Step 4. CHECK THE VOLTAGE AT THE SOLENOID VALVE WHILE THE KEY SWITCH IS ON AND THE PARKING BRAKE IS RELEASED


Turn the key start switch to the ON position. Press and release the parking brake switch.
Note: Two people will need to perform this procedure. One person will need to be sitting in the seat with the armrest in the DOWN position.

Measure the voltage across the two contacts of the harness connector (A958-WH and 202-BK).
Expected Result:

The voltage should be greater than 10 DCV.

Results:

• 
  OK - The voltage is greater than 10 DCV. Proceed to Test Step 5.
  
  NOT OK - The voltage is less than 10 DCV. Proceed to Test Step 7.

Test Step 5. CHECK RESISTANCE OF THE SOLENOID


Measure the resistance between the two wires of the parking brake solenoid.
Expected Result:

The resistance should be 10 ± 2 Ohms.

Results:

• 
  OK - The resistance is 10 ± 2 Ohms.
  Repair: The problem does NOT appear to be electrically related.
  Stop.
  
  NOT OK - The resistance is NOT 10 ± 2 Ohms.
  Repair: The solenoid has failed. Replace the solenoid.
  Stop.

Test Step 6. CHECK THE WIRE HARNESS FOR A SHORT CIRCUIT


Locate the Interlock ECM.

Disconnect the wire harness.

Turn the key start switch to the ON position.

Check the resistance from contact 13 of the wire harness to the following contacts: contact 1, contact 11, contact 24, contact 29, contact 62 and contact 70.
Expected Result:

The resistances should be above 2 Ohms.

Results:

• 
  OK - The resistance readings are above 2 Ohms.
  Repair: The ECM is unlikely to fail. Terminate this procedure and restart the procedures. Verify all the readings.
  Stop.
  
  NOT OK - One or more resistance readings are below 2 Ohms.
  Repair: The wire harness has failed. Repair the wire harness or replace the wire harness.
  Stop.

Test Step 7. CHECK THE WIRE HARNESS FOR CONTINUITY


Turn the key start switch to the OFF position.

Connect a jumper wire between wires A958-WH and 202-BK on the wire harness at the end of the parking brake solenoid.

Locate the Interlock ECM.

Disconnect the wire harness.

Check the resistance between pin 13 and pin 66 of the wire harness.
Expected Result:

The resistance should be less than 2 Ohms.

Results:

• 
  OK - The resistance is less than 2 Ohms.
  Repair: The ECM is very unlikely to have failed. Reconnect all connections and visually inspect the wire harness. Verify that the diagnostic code still exists. If the diagnostic code still exists perform the Test Steps again.Replace the ECM, if the cause of the diagnostic code was not found after the second attempt. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".
  Stop.
  
  NOT OK - The resistance is greater than 2 Ohms.
  Repair: The wire harness has failed. Repair the wire harness or replace the wire harness.
  Stop.

 

[Nige]

Is there a procedure like the one below but for my machine?

No. The electronic system is totally different on your machine. That’s also why you can’t find 202-BK, because it’s not there……..

I tried to explain this to you in an earlier post.

What would the name or the function of that wire be, in case I can look it up that way.

You obviously didn’t read the schematic too closely. There is a table in it that will answer that question.

 

[franm]

Apologies for the misunderstanding earlier.

Update: Park brake solenoid seems to work fine, with voltage and resistance within expected paramters.

Just a quick question. Can this machine (or any of its kind) move when connecting the park brake solenoid directly to 12V, as a temporary workaround? Or is there something else inbetween that would prevent the machine to move in spite of forcing the solenoid valve to 12V?

 

[Nige]

Just a quick question. Can this machine (or any of its kind) move when connecting the park brake solenoid directly to 12V, as a temporary workaround? Or is there something else inbetween that would prevent the machine to move in spite of forcing the solenoid valve to 12V?

If the PWM signals from the joystick position sensor are not what the ECM is expecting then the machine is unlikely to move even if you jumper the parking brake solenoid with 12v. It is those PWM signals that cause the ECM to send power to the hydrostatic pump solenoids that makes the machine move.

 

[franm]

Update:

Unplugged the harness from the park brake solenoid valve and connected the valve directly to the 12V from the battery. It makes the trigger sound, so the valve works. However, upon starting the machine and tilting the left joystick in any direction, the machine just won't move. On the left hand panel the park brake light is on.

So as you said, it might be that the ECM is interpreting based on the PWM signal from the joystick's sensor that the joystick is already "tilted" at the time of starting the machine and so blocks the hydrostatick pump valves based on that information and then you can't move the machine for safety reasons.

I'm thinking of swapping the left joystick with the right, and see how the bucket responds in that scenario.

 

[Nige]

I'm thinking of swapping the left joystick with the right, and see how the bucket responds in that scenario.

Just be careful. The Part Number of the LH & RH joystick bases are not the same. 269-0258 LH versus 269-0257 RH.