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Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 989
Experience:  Technican turned service manager with multiple lines of equipment and rental units.
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Cat 420E: I have a cat 420 E backhoe I am having a problem

Customer Question

I have a cat 420 E backhoe I am having a problem with the extendable stick checked the switch power to it but no power at solenoid there is also a problem with trans it pops out of 3&4 it s a4 speed auto trans
Submitted: 1 year ago.
Category: Construction and Road Equipment
Expert:  catmastertech replied 1 year ago.
Hello,I see no one has helped you with this problem, I would like to assist you if you still need it.I am not sure how much you can test without the use of ET service software the dealer has but, if you will post the machine serial I will see what I can find that may help.
Customer: replied 1 year ago.
serial number 04920EHKMW0136
Expert:  catmastertech replied 1 year ago.
Thanks for the reply. Please verify the serial number, it is no a correct number. I need to know the last 5 numbers after KMW-----.You stated your transmission is Autoshift, is this correct? Most Autoshift transmissions are 5 speeds. This version has a rotating handle for all speeds with an autoshift button on the dash.Some items that may cause this problem are;The transmission does not operate in any speed or the transmission does not engage in all speeds.Probable causesThe neutral lockout switch is engaged. (or has a poor connection)The parking brake is set or the parking brake switch has failed. (or adjustment maybe too close and making contact when driving)An electrical failure in the shift control or a damaged transmission control fuse.The transmission has a mechanical failure.Clutch discs and plates have too much wear.The seals leak.Problem 2The transmission does not shift into fifth gear.Probable causesThe speed sensor is not adjusted correctly.The autoshift switch is in the manual mode. For your backhoe issue, please tell me which side thumb control is giving you a problem?Do you have two thumb controls and are they both on one lever or both levers?What other backhoe options/attachments are installed on this machine?
Customer: replied 1 year ago.
T.he thumb control is on the RH joystick for extend boom . The transmission you can be driving in3 or 4 machine stops put in it netural play with shift lever it works for a little sometimes put shift lever half way between 2&3 it will or half 3&4
Customer: replied 1 year ago.
sometimes stops in all gears
Expert:  catmastertech replied 1 year ago.
Thanks for the update. Can you please verify the serial number?Do your transmission neutralizer switches work correctly? One is on the loader control lever. If these are sticking or the wires are shorted, it could cause the transmission issue.I will look for details about your thumb controls as soon as I can get the correct serial number. What did your testing of the thumb rocker indicate? Did you test the wires from the handle to the ECM?
Customer: replied 1 year ago.
040EHKMW01361 there is power going to the rocker 3 wire going it 2power 1ground 4 wires coming from the rocker no power at solenoid . I didn't check the switch in the lever . could it be a forward or reverse solenoid I will check those things next trip to job site
Expert:  catmastertech replied 1 year ago.
No common solenoid will cause the transmission failure you are seeing. The only common item is the return feed wire in the transmission harness. The 975 white wires are tied together in this harness. A poor connection could be your trouble. Test the harness for shorts, opens or continuity from the solenoids to the harness connector. I will attach a drawing of the transmission harness.The same applies to the E-stick control. The only thing common is the return feed. The E540 pink wire should be checked for shorts, opens and continuity back to the ECM. Attached below is the drawing of the Control and the ECM. One known failure has been found in the transmission but, I don't see it as related to your issue. Pressure testing will be needed to verify the issue but, most of these transmission have already been fixed under a service letter repair. Here are the details.The existing 2nd/3rd clutch shaft assembly used in the powershift transmission may crack on certain 420E, 430E, 432E, 434E, 442E, 444E, and 450E Backhoe Loaders. If the existing shaft assembly cracks oil can leak into the clutch piston cavity causing the clutch to partially engage. This will cause the clutch to fail. If the existing shaft assembly cracks, it can be replaced with an updated shaft assembly. This machine does not have any other access to view fault codes. The only way to reduce the troubleshooting time and quickly locate the problem is to connect the service program ET and check for active fault codes. The dealers can check this for you or maybe a local shop has the ET program can do it. It is available but, it is expensive most small shops or independents would not purchase it.If you check through these item and find something you need more help with, just let me know and I will try to narrow done some possibilities. I wish I could provide more help but, without the fault codes it will be slow going. I will be glad to help all I can. Thanks, Donnie
Customer: replied 1 year ago.
I am still having transmission trouble with the 420E Cat backhoe
Expert:  catmastertech replied 1 year ago.
What have you done so far?Can you get the codes checked by the dealer?
Customer: replied 1 year ago.
New problems. The transmission won't work in any gear forward or reverse. Also the backup alarm doesn't work.We have check the grounds and everything seems okay.
I found the E540 pink wire on the controller but don't know where to check for continuity
Customer: replied 1 year ago.
Also plugged in the switch on the joystick and the forward/reverse lever but still nothing
Expert:  catmastertech replied 1 year ago.
The E540 wire is from the controller to the auxiliary valve 2 return feed.It is not part of the transmission controls.What switch and on which joystick are you referring?
Customer: replied 1 year ago.
We tried a new joystick for the bucket controls and a new forward/reverse lever
Expert:  catmastertech replied 1 year ago.
Sounds like you have tested all you can. Can you get a dealer to check the codes?
Customer: replied 1 year ago.
Can you email a diagram labelling the transmission seleniods?
Expert:  catmastertech replied 1 year ago.
I already sent you a diagram.
Expert:  catmastertech replied 1 year ago.
This is computer controlled. Do not apply full voltage to any of the solenoids or they may burn out quickly.
Customer: replied 1 year ago.
There are 5 solenoids on the transmissions. I would like a diagram of the function of each solenoid
Expert:  catmastertech replied 1 year ago.
Did you tell me this was an Autoshift transmission?
Customer: replied 1 year ago.
Yes
Expert:  catmastertech replied 1 year ago.
Then the diagram I sent is correct.It even had a function chart to show the solenoids with the selected gears.Did you see it in the other post I sent you. It was just before the E-stick wiring.
Customer: replied 1 year ago.
I'm looking for a picture of the transmission showing each solenoid. From the diagram you sent there is no way to know which solenoid is which by looking at the transmission
Expert:  catmastertech replied 1 year ago.
I am not sure I can find a picture. I will look to see what is available.I normally use the wire number and colors to verify the solenoid I am on.
Customer: replied 1 year ago.
There is a lot of mud and dirt underneath the floor boards. Finding the number on the wires is probably going to be impossible
Expert:  catmastertech replied 1 year ago.
Just don't spray the wires with brake cleaner. That can wash the numbers off. Here is what I found.
Customer: replied 1 year ago.
What is the voltage for the solenoid. I tested the forward low solenoid and the voltage was only 0.65V. I was expecting 12V
Expert:  catmastertech replied 1 year ago.
These are computer controlled. They will not see full voltage.
Customer: replied 1 year ago.
What should be the voltage on the forward low solenoid when the machine is started and put in gear?
Expert:  catmastertech replied 1 year ago.
The solenoid valves are an output of the machine ECM. The solenoid is the proportional type. The ECM uses a pulse width modulated signal (PWM) to vary the current to the solenoid. The distance that is travelled by the solenoid valve is proportional to the electrical current. The position of the valve opens or the position of the valve blocks the flow of oil to the hydraulic cylinder.Solenoids control the oil flow to the clutches in the transmission. When a direction and gear are selected by the operator, the control module activates the appropriate solenoids. Two solenoids are activated in order to move the machine. One solenoid is activated for the direction and one solenoid is activated for the gear. When a solenoid is activated, a solenoid receives voltage from the control module. When the transmission is in neutral, no solenoids are activated.The solenoids have a connector with 2 contacts. One contact receives power from the corresponding connector contact (signal) of the control module. The other contact returns to the control module. All of the solenoids have a return lead. The return leads join together with the other return leads.
Expert:  catmastertech replied 1 year ago.
The manual does not publish any exact voltage.This is controlled by the computer and will vary the load as need to operate the solenoid.You may find an AC current show a better number. The only way to see what is wrong is to use CAT ET program.
Expert:  catmastertech replied 1 year ago.
The information I posted above is all the manual list for the solenoids.
Customer: replied 1 year ago.
Hooked up 12V Direct Power to the forward low solenoid and the transmission goes into gear. As I said before the actual power going to the solenoid is less than 1V. How can we trace this voltage.
Expert:  catmastertech replied 1 year ago.
Check continuity from the solenoid to ECM. Use the first three or four digits to identify the circuit. The last numbers are the color and harness id numbers.Check the output at the harness from the ecm using a "spoon" or needle probe to see if the ECM is sending out voltage.It is slow going but, you may identify a poor circuit.Still, using ET would should immediately show were the fault is locatedI also sent you a diagram of the ecm connector.You may need to purchase a schematic from your dealer to help find all the connectors.I cannot provide the schematic as it is copyrighted material and I will be removed from the site for a policy violation.

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