First post so move if needed, I have a John Deere 210Le, SN885962, that I has been throwing a coolant overheat light, Steady Coolant Overheat and steady Stop Light when it happens, the thing is it isn’t actually overheating at all, figured it was just a bad coolant temp sensor. Installed a new one along with a new thermostat, and it still throws the Overheat light after about 5-10 minutes of use. The reason I know it’s not actually overheating is I Measured resistance of both the old and new temp sensor, and they measured virtually the same cold soak and at 195 degrees. So thought I would check some basic wiring, power stays right around 5V, on the green power wire. And checking resistance in the wire it measured virtually identical to the Fuel Temperature Sensor right below it. Moving on to ground I was at 1 Ohm of resistance from the connector ground to an actual ground on the frame/engine. Called up a local John Deere parts dealer and said for my unit it’s a known problem for the Ecm to go bad and throw false overheat warnings. My thinking is if the parts dealer is correct and the Ecm is bad it’s throwing it once the Ecm gets hot after some run time on the engine. Don’t want to shell out a grand for a computer unless I’m sure that’s the problem. As they said reflashing the computer usually dosen’t work. Could anybody help point me in the right direction about testing the Ecm for this problem, post some detailed wiring diagrams, etc. Or even just if anyone has had similar problems and fixes, any help is appreciated. Also, pulled flash codes to see if I had any, No Active Stored- 25- Manifold Air Temperature Input Voltage High
Welcome to HEF Steamy ! Did you measure the voltage at the temp sensor (yellow wire) by backprobing? If not, do so while it is showing the overheat condition. Also measure the black wire the same way. Then move to the ECU and measure the same wires there (terminals B1 and D3). Post results. Very true. I have replaced many ECU's for that condition. Let's wait to see the results of the electrical readings at both ends.
Yes, Voltage with it running and throwing the light stayed around 4V to 5V, Black wire I did not, assuming it was ground I only checked the Resistance to ground with it running and off. I noticed you said yellow was the power wire, I saw the same thing in the Manual, but looking at the wire going to the sensor, the power wire is green. As for checking at the ECU, could you post the which wires coming out/in the ECU are B1 and D3. I would assume since the ECU is all weather sealed it would be pretty hard to back probe, assume I would just have to poke the wire, measure the Voltage, then dab a tiny amount of liquid electrical tape to seal it back up. I am out of town and will be for another couple weeks, that’s why I posted this now, so as for further testing I won’t be updating this for around 2 weeks, If I post again to this thread later, will it update it in the fourm and bump it up?
It is not hard. Use the item below. Don't poke holes in wires. Measure the black wire at the sensor by backprobing when you are back. Ohm's reading of wires are only useful for testing for an open circuit. It will usually not find a corroded wire as many people think. Voltage drop testing is the only proper way to test wiring, IMO. As far as the ECU pin-out, check your messages.
@mg2361 I have stated that same thing many times here. Resistance checks are not really a good check of a circuit, especially high current circuits like starters. A very small resistance can cause enough of a drop for slow cranking or no cranking. I my day job I am a field engineer for a major car company. You would be amazed at how many so called "A techs" have no clue how to do a voltage drop test.
Okay, I will be available tomorrow hopefully to go look at the machine again, to double check and make sure it is the ECM. I do want to explore options on the Ecm, I got quoted $1900 for the Ecm alone, plus I would have to pay a service call to have the Ecm programmed, which can get very expensive very fast. I am just wondering is there any Ecm repair places online for John Deere 210 Ecm? I found a lot of places for Cummins, cat, etc. But I couldn’t find one for John Deere 210 Ecms. Also, can any mobile mechanic with John Deere Software be able to program a new Ecm? I think it would be cheaper than the parts store service call. Also does the Ecm have to be on the machine to program/flash the old Ecm onto the New one.
If you buy your ECU at the dealer, they should have the means to program it before you take it home. We program all engine controllers here in our shop when a customer buys one over the counter. We charge 1 hour labor for the programming, which is added to the parts invoice. Just make sure you have your old one with you. They need it to pull information off it to put onto the new one, plus for the core charge. I have not used any controller repair facility for a Deere controller, so I would not be able to recommend one.
That’s kind of what I assumed, I have found one place online that specifically mentions they repair the John Deere Ecm for my machine, forgot the number off the Ecm already. A couple things though about the temp light coming on. I backprobed the ECM and the Dash on G2 or G3 I forget which one was the Wire that goes to the dash display for the temp light. I got 12V on both the Ecm and the Dash with the engine running and no temp light, and I was testing out what makes the Temp Light come on, and found out that if I backprobe the wire coming from the Ecm and ground it with a test light it activates the temp light/stop light. So originally I thought the power was coming from the Ecm but what I’m understanding now is the the Monitor display feeds the wire going the the Ecm and the Ecm just is a ground control for the temp light, which basically gets the signal to ground the Temp Light Wire, through the input of the Coolant Temperature Sensor going into the Ecm. So now another thought, could my Dash Display Monitor be grounding that Temp Light wire causing it to activate. I’ve tried jiggling it around, tapping it, messing with the wires, etc. Couldn’t think of anything else, besides the obvious Problem of the Ecm Being Bad. Just trying to rule every possibility out. Thanks again to everybody who responds
The ECU controls the ground for the temperature light on the monitor. Check your messages.
Just wanted to update this thread, I did end up getting a new ECU a while back and the False overheat is fixed.