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Dan
Dan, Technician
Category: Construction and Road Equipment
Satisfied Customers: 4998
Experience:  17+ yrs. shop and field experience with all major brands of heavy equipment and trucks - 1995 WyoTech graduate.
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Komatsu WB140-2 #F110xx Backhoe Loader |=| Problem: Starter

Customer Question

Komatsu WB140-2 #F110xx Backhoe Loader |=| Problem: Starter won't turn over. |=| Background: When I short relay K01 (Starting Relay) pins 30 and 87, then it starts just fine using ignition key. The voltage across K01 pins 85 & 86 is 9.8v and does NOT activate
the relay. The relay tests OK out of circuit and I also tried swapping K01 and K02 but same problem. I believe the problem is the voltage across 85 & 86 is too low to activate K01 relay. |=| Question: How do I repair this problem?
Submitted: 1 year ago.
Category: Construction and Road Equipment
Customer: replied 1 year ago.
Komatsu WB140-2 #F110xx Backhoe Loader|=| Problem:
Starter won't turn over.|=| Background:
When I short relay K01 (Starting Relay) pins 30 and 87, then it starts just fine using ignition key.The voltage across K01 pins 85 & 86 is 9.8v and does NOT activate the relay. The relay tests OK out of circuit and I also tried swapping K01 and K02 but same problem.I believe the problem is the voltage across 85 & 86 is too low to activate K01 relay.|=| Question:
How do I repair this problem?
Customer: replied 1 year ago.
Komatsu WB140-2 #F110xx Backhoe Loader|=| Problem:
Starter won't turn over.|=| Background:
When I short relay K01 (Starting Relay) pins 30 and 87, then it starts just fine using ignition key.When I turn ignition to Start, the voltage across K01 pins 85 & 86 is 9.8v and does NOT activate the relay. The relay tests OK out of circuit and I also tried swapping K01 and K02 but same problem.I believe the problem is the voltage across 85 & 86 is too low to activate K01 relay.|=| Question:
How do I repair this problem?
Expert:  Dan replied 1 year ago.

Hi my name is***** will be glad to try to help. Check the ground terminal of the relay and try grounding it separately and let me know the results....

Customer: replied 1 year ago.
Hi Dan,Yes, when I short the ground terminal (pin 86) of relay to ground, it snaps closed and then starts normally from ignition key.
Expert:  Dan replied 1 year ago.

thanks for the update. I was trying to grab a schematic for your machine to help. I do not have one for this model. Verify the shift control is in neutral and passes a continuity test or the machine will not be allowed to crank over. I did find a reasonable priced manual if interested with full schematics and test specs. https://www.tradebit.com/filedetail.php/130118118-komatsu-wb140-2-wb150-2-backhoe-loader-service-shop

Let me know

Customer: replied 1 year ago.
Dan,I purchased the manual and you can view it from this link http://www.investlabs.com/TempDownload/Komatsu-3MPEBK2Q/Komatsu%20WB140%20Wb150%20Service%20Manual%20DRD%20Marked%20up%2020151107.pdfYou will need to zoom in a bunch on the pdf to see the wires. I have highlighted the wires that affect the relay K01. Green goes to ground, red goes to hot.Here is some more info from today's diagnostics, referring to electrical diagram on page 109 of manual:
1) If I short the diode XAD, it starts fine.
2) The diode at XAD tests fine with multimeter in diode test mode. 520mv and 0 the other way.
3) The resistance at alternator G2 measured from XA alternator pin Z-B1 to ground is 5K Ohms. This is with the XA connector unplugged.
4) Battery voltage with engine running is 15.2v
5) Continuity tests ok from pin 86 of K01 to XA Z-B1 (with cable unplugged from alternator)I look forward to your insight. Is the 5K Ohms at the alternator normal?Thank you,
Doug
demingdr at gmail.com
Customer: replied 1 year ago.
I also just uploaded two pics of the alternator. The XA Z-B1 wire is the purple/white in the close up shot.
Expert:  Dan replied 1 year ago.

Thanks for the info Doug. Question... What is your battery voltage. I am trying to determine why you are only getting 9 volts through the K01 relay I will need more time to print and study the schematic. My first suggestion before getting too deep into this is with all connectors connected and fuses and relays checked and their connections is to do a wiggle test on the harness and try to manipulate the harness and connectors with someone working the IGN switch to see if there may be a bad connection in one of the connector pins. Also I would inspect and clean the harness grounds shown in the schematic. I am not sure if I will be able to offer much time to work on this tonight and tomorrow as I have family in for Veterans day but if you would like I can opt out in case someone can pick up where we have left off. Let me know. This will likely require a decent amount of time running through the schematics, etc. If no one has been able to pick up the question I will jump back in but will likely have to send you an additional services link on this one due to the extra amount of time this will likely take if you are ok with that. Let me know

Customer: replied 1 year ago.
WIth K01 pulled out, the hot side of socket K01 pin 85 to ground measures 12.3v. However, it only measures 9.8v from pin 85 to pin 86. The battery measures 12.3v from hot to ground.Yes, please opt out of the case for now and then pick it up again if no one else has.Thank you.

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