How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Kevin Your Own Question
Kevin
Kevin, Technician
Category: Agriculture and Farm Equipment
Satisfied Customers: 731
Experience:  Over ten years of expirence in Ag Electronics and Hydraulics
32685367
Type Your Agriculture and Farm Equipment Question Here...
Kevin is online now
A new question is answered every 9 seconds

I have a Deere 8420 and I ran it two weeks ago with no

Customer Question

Hello, I have a John Deere 8420 and I ran it two weeks ago with no problems. It has been sitting outside and when I went to turn it on it wouldn't start. When your first turn the key the code PCU 5 comes on and after about 30 sec it goes away and code CCU 7 comes on and stays.
Submitted: 1 year ago.
Category: Agriculture and Farm Equipment
Expert:  Kevin replied 1 year ago.

Hello, my name is ***** ***** I can help you with your question.

The two codes in question most often occur just after the PCU/CCU controller has been replaced. The PCU 7 code indicates that no successful transmission calibration has been performed and a no load torque calibration value has not been saved. If the codes suddenly occurred and the controller has not been replaced then it is a sign that the controller may be in the process of failing. Often the loss of the calibration data which is indicated by the two codes means the controller has lost or is loosing the ability to access its permeant stored memory. I'm also concerned by the fact that the PCU 5 code goes away which means the CCU/PCU starts receiving and processing the engine load data from the ECU. This again is an indication of a failing PCU/CCU controller. There is a chance that the controller has gotten moisture inside it which is causing the problem. Unfortunately about 90% of the time the screws that hold the two halves of the controller together will break in the process of opening it up to check for moisture.

If you loosen the four 10mm head bolts that retain the rear cab cover on the outside you can slide the cover off. The lower center controller should have a white label on it that will indicate it as the CCU/PCU controller. With the key off us a 1/4" nut driver and remove the connectors from the controller at both ends. Next remove the controller from the back of the cab. If you can shake the controller and hear something loose or what sounds like water then the controller is most defiantly failed. Since the CCU/PCU controller stores the tractors engine hours they should be replaced by a dealer so that the correct information is put back in. In addition the transmission and PTO will need to be calibrated following replacing the controller along with several other inputs.

Please let me know if I can be of any further assistance.

Thanks,

Kevin

Customer: replied 1 year ago.
Hello Kevin,I did as you said and removed the cover and shook the controller and I went ahead and shook all of them and none of them made any loose noise. They were all quiet. The John Deere mechanic said the CCU 7 and the PCU 5 code that goes away indicated the oil pressure guage sensor was bad. I replaced that as well and still the tractor will sound like it is about to start but never turns over.
Customer: replied 1 year ago.
Also in the cab the oil pressure guage itself shows it has very low oil pressure.
Expert:  Kevin replied 1 year ago.

Actually the CCU 7 code indicates that the engine power level doesn't match the CCU controllers power level based on model. We do periodically see the CCU 7 code when an aftermarket power enhancing device has been installed on the tractor. I do apologize however as I mistakenly looked both codes up previously as PCU codes instead of the CCU 7 code. The PCU 5 code is indicating that the PCU is not receiving fuel flow data from the ECU. Most of the time this code is set by the PCU due to a delay in the communication. Unfortunately most of the time the delay is caused by the CCU/PCU controller however not always. I don't see how either of the two codes at all relate to the oil pressure sender. It might be worth trying to clear the two codes to see if they come back. The following steps will walk you through the procedure.

  1. Open the fuse panel and place a spare fuse in the empty port labeled "DIA".
  2. Turn the key to the run position, the corner post should read "DIA".
  3. Use the turn signal switch as if making a right turn until CCU is displayed.
  4. Pull the turn signal switch towards you to the flash to pass position and release to enter into the CCU controller.
  5. Use the turn signal switch as if making a right hand turn to access address 001.
  6. Once 001 is selected it will scroll through the stored codes list followed by the word "End", with end displayed turn the red warning lamp switch on and back off thus clearing the stored codes. If no codes are active the display will then read "000" if the display continues to cycle and show CCU 7 then the code is active and cannot be cleared until resolved.
  7. Repeat steps 1 through 6 on the PCU controller. If the codes cleared turn the key off and remove the fuse from the diagnostic terminal. Operate the tractor to see if the codes return.

Let me know what you are seeing as I will gladly assist you with further diagnostics as needed.

Thanks,

Kevin

Customer: replied 1 year ago.
Hello Kevin,I was just curious if the oil pressure guage in the cab matter at all. It is reading that it almost has no pressure.
Expert:  Kevin replied 1 year ago.

During cranking I don't expect the engine oil pressure gauge to move at all but once running you should show good oil pressure. The engine oil pressure sensor is connected to the ECU controller, the ECU then sends the signal on the communication network to the CCU/PCU. The CCU/PCU then transmits the engine oil pressure to the ICU controller which is the display. What I'm wondering now is if we have an ECU problem. Use the steps i previously provided and check to see what ECU codes are showing up. If the ECU has codes clear them. Attempt to start the tractor and then go back in to see what ECU codes were set.

Let me know what you are seeing when you get time.

Thanks,

Kevin

Customer: replied 1 year ago.
Hello Kevin, sorry I didn't get a chance to check yesterday but I did as you said and cleared it and the codes returned after clearing it. Code PCU 5 wouldn't clear though but CCU 7 did but came back.
Expert:  Kevin replied 1 year ago.

At this point lets check to make sure that the F27 and F43 fuses are both good. Also when you were accessing the addresses to clear the codes did you see ECU in the controller list? You can follow steps 1 thru 3 above to verify the ECU is displayed. Will the tractor at this point start?

Let me know when you have time.

Thanks,

Kevin

Customer: replied 1 year ago.
The fuses were fine, I was able to see the ECU display and the tractor still will not crank.
Expert:  Kevin replied 1 year ago.

The starting circuit is not dependent the computers a whole lot. The only part that the controllers are responsible for is neutral start. If the corner post display shows "N" then it should allow the engine to crank. The starter relay is located just below just behind that horizontal exhaust pipe at the right front of the cab. When you turn the key to the crank position see if the starter relay clicks. Also listen for any signs of the starter solenoid on the starter itself clicking. Let me know what you are finding and I will provide you with a diagnostic procedure that will let you work thought the starting problem.

Thanks,

Kevin