Tractor Repair: Kubota L2900 Glow Plug Malfuntion, timer module, glow plugs

Question
Kubota L2900 DS GST - The Glow plugs stay on for extended periods. I just bought this tractor and the dash light was burnt out. When I replaced it I noticed it would remain on even after the tractor started. I have verified there is power to the glow plugs when the light is on. the part guy at the Kubota dealer told me there is a relay as well as a controller, but couldn't tell me the location of either. Each part cost over $50 and can't be returned. I have good mechanical ability, and can do most tests with a volt meter. I have also found that the key will not shut off the engine as the operators manual says it should. I am less concerned about this, but it may be part of the glow plug problem. I have not started using the tractor yet, and I have seen the glow plugs turned off and verified no power to them. I assume they should operate for a short period and then switch off.
Thanks for your help...Eddie

Answer
Hello,

  I am not an expert on Asian or European tractors as stated in my profile, but here is some info that I have found.  Yes, the glow plugs should operate for a short period and then switch off.  The length of time depends on the engine temp. which is monitored by the thermistor.  The problem of glow plugs staying on too long is caused by the controller, not the relay.  There is no actual test for the controller, it is done by the process of elimination by testing the thermistor, relay, and switch.  If everything else tests OK, replace the controller.  It is located under the dash.  It may be normal for the glow plug light to not go out immediately after starting, but should not stay on for more than a few seconds after starting.  As you have probably found out already, the controller is about $65.  And you are correct, no electrical parts are ever returnable.

   The engine not shutting off with the key is a separate issue not related to the glow plug problem.  There is a shut-off solenoid and timer module, but that's all I know about it.  Could be a problem with either one.  Check solenoid coil with an ohm meter.

         Hope this helps a little.

                       Arnie