G1800; Glow Plug light

[CIT]

I have a G1800 with glow plug light NOT illuminating (at the dash) when ignition switch is turned to "pre-heat" position.
Ignition switch has been tested in all positions with positive results.
The glow plug light bulb has been tested; it is good.
I have continuity from the ignition switch (in "pre-heat" position) to the Combination Box through the 1 25RB circuit.
The 15 Amp fuse is good.
I have continuity from the glow plug light to the Combination Box through the BrR circuit.
I have current from ignition switch (in "pre-heat" position) to the the glow plugs at the engine.

Any thoughts and or suggestions as to why the glow plug light is not illumination?
Thank you.

 

[Dave_eng]

I have a G1800 with glow plug light NOT illuminating (at the dash) when ignition switch is turned to "pre-heat" position.
Ignition switch has been tested in all positions with positive results.
The glow plug light bulb has been tested; it is good.
I have continuity from the ignition switch (in "pre-heat" position) to the Combination Box through the 1 25RB circuit.
The 15 Amp fuse is good.
I have continuity from the glow plug light to the Combination Box through the BrR circuit.
I have current from ignition switch (in "pre-heat" position) to the the glow plugs at the engine.

Any thoughts and or suggestions as to why the glow plug light is not illumination?
Thank you.

I cannot find WSM for your model.

While not your specific tractor these test procedures would provide more info.

For example, it is common for Kubota to power the GP's in both pre-heat and START positions of the key switch.

You only mention current in pre-heat.

Test for voltage in both key positions.

Measure the resistance of the GP's with the wiring disconnected.

Is this situation one that has developed with the warm weather? Is there more history?

p.s. A friend has provided some manuals.

This is the Troubleshooting chart for instances when the glow lamp does not light.

The starting instructions lead me to think the engine temp sensor is providing an input to the combination box which varies the pre-heat time of the GP's

Testing the engine temp sensor would be an easy step.

Dave

 

[CIT]

Thanks Dave_eng, for your response and technical assistance with troubleshooting suggestions along with quantitative specifications in pursuit to determine why the glow plug light does not CONSTISTENLY illuminate during the 'preheat' cycle in preparation for starting.

Below is a list of results and other information recently obtained.

Date of troubleshooting; 6/2/2021.
Ambient temperature: 72 degree F
Machine hours: 498
Battery voltage: 12.31 Volts.

Lead Terminal Voltage tests:
Voltage at glow plug wire-BR (to chassis ground) during preheat cycle: 12.17 Volts.
Voltage at glow plug wire-BR (to chassis ground) during start cycle: 12.16 Volts.

Glow Plug Continuity tests:

Front glow plug: 1.2 ohms
Middle glow plug: 1.2 ohms
Rear glow plug: 1.2 ohms

Additional tests:

Verified continuity on the BrR wire (glow plug light) from the bulb at the dash all the way to the corresponding pin inside the round shell connector which mates to the Combination Box connector.

Verified that the glow plug lamp bulb is functional. Also, I do have current through the RY wire going to the glow plug light at the dash.

Verified continuity of the ignition switch in all positions.

All fuses are good.

The starter is functional and the engine does start. However, with ignition switch in "off" position, the ESS is NOT triggered to activate the fuel shut off valve. This too is intermittent.

Summary:

Glow plug light (at the dash) continues to be intermittent.

Is there a way to test functionality of the Combination Box? Surely there are resistors, TDR's, etc inside that box.

Again, any technical experience or troubleshooting is appreciated.

Thank you.

 

[Dave_eng]

The combination box is one of those lovely components where no specific tests are available, rather if a series of function tests fail then you conclude the combination box is faulty.

If your stop solenoid passes this simple test, I would be very suspicious of the combination box.

The operational tests need to be done meticulously. Short cuts lead to mis diagnosis!

Dave

 

[lugbolt]

wiring issues and grounds were big issues with the G1800/1900 mowers. Scrutinze the connectors AND grounds carefully. Grounds especially-as poor grounding is generally what took out the combination boxes. They revised the boxes to make them a little more tolerant to voltage spikes but it doesn't solve poor grounding.

You ideally will want to use a voltage drop test to find your issue. Using that test, you will find your issue somewhere in the circuit, whether it be at the wiring between the connector and the panel, or ground.

I had an old tech show me the drop test procedure years ago, on of all things a G1900-S (which I eventually purchased from the customer that owned it at the time). On that particular one we were able to isolate the cause in under 30 minutes time, it was a problem with one of the harness connectors. It was showing a 1.6v drop across the connector which was causing our particular problem. Mind you, as a "novice" tech at the time, I had no idea what the drop test did, but after he showed me, it became apparent that one can also use it on ground side. After I bought the G1900, I too had electrical issues pop up here & there, sometimes while mowing. Using the drop test I found bad ground between the engine & chassis, showing 6.2v drop between batt - and chassis ground. Added another ground wire, all problems solved.

Drop test is done on a loaded circuit rather than just ohming wires. One strand of wire can carry enough current to make your DVM read 0.0 ohm via normal continuity test (no load on the circuit), which would be considered "good", but that one strand can't carry enough current to make a glow system work--and that is where a drop test would show your issue plain as daylight.

To find how how to do a drop test, search it on youtube. It's an invaluable tool in your toolbox--especially if you own a G1800 or G1900.