310SJ temp gauge goes to hot on engine startup

[vikingsven]

Need some help diagnosing an issue with my 310sj. A few days ago, I went to start it up cold and the temp sensor went to full hot and I got an engine overheat warning. I shut it down and restarted. Same issue. On the third attempt it didn't alert and the temp gauge displayed properly.
I changed out the coolant temp sensor. Same issue. Unplugging the temp sensor when the engine is running returns the temp gauge to cold, but I get a temp sensor fault code which I expected.
Plugging in the original sensor with the engine running, but not installed, pegs the gauge. Unplugging it returns the gauge to cold.

The wiring to the sensor looks to be intact and in good shape. I am going to investigate this more thoroughly as well as look for any corrosion on the pins.

Is there anything else I can check? Reference voltages should be what at the sensor? Really hoping this isn't an ECU issue...

Thanks in advance

 

[mg2361]

A machine serial number would help since there is multiple electrical variations and different ECU's.

Reference voltages should be what at the sensor?

That is a 5 volt circuit. That 5 volts varies based on the resistance of the sensor. It should read between 0.5 volts and 4.5 volts, depending on the temperature. If it hits 0.1 or 4.9, it will throw a code.

 

[vikingsven]

Thanks for the response mg2361!

Serial number is T0310SJ144440

 

[mg2361]

Check your messages.

 

[vikingsven]

Is the 5 volts from the ECU supplied to the sensor on pin D1 or B3?

 

[mg2361]

Pin B1 (yellow wire) from the ECU, which travels to pin A of the B15 coolant temp sensor.

 

[vikingsven]

Ok. That makes sense.
So yellow B1 should be outputting 0.5 to 4.5v depending on the resistance. With the sensor disconnected it should be 5v?
Assuming the sensor is good, what's the best method to troubleshoot this?

Thanks again for the info so far.

 

[mg2361]

With the sensor disconnected it should be 5v?

Correct.

Do you have any active or stored codes in the monitor you can post?

Assuming the sensor is good, what's the best method to troubleshoot this?

I would backprobe the ECU B1 terminal and monitor the voltage. If the voltage drops, it will send the gauge high, which would be a wiring issue. If the voltage does not drop, but the gauge goes high, then I would suspect an ECU issue.

 

[vikingsven]

No active codes other than the sensor fault from unplugging it. There are a few stored codes related to a seat position sensor, which I am aware of and not relevant here, but I'll re-check.

Thanks again for your help. I'll report back what I find when I get a chance to run some tests.

 

[vikingsven]

Finally got some time to go through some testing:
I found that the voltage at the temp sensor to be 4.9v initially. After 10m or so of troubleshooting the voltage was ~3.5v. Not sure if this is normal? I checked all the wring again and it all looks ok. With the sensor disconnected I get error code 110.04, ECU coolant temp sensor. Plugging the pig tail back in does nothing, so I suspect there may be an issue with the sender still. I'll order another one.
Interestingly, when I had the wire disconnected and my multi-meter plugged in to the temp sensor connector, there was no error code thrown and everything behaved as it should, so again, I think the sensor may be the culprit.

 

[hoedown]

vikingsven, Did you find out where your problem was? I have a SJ 310 as well with the same issue. Serial 148920. I put a new temp sensor in, but the problem did not go away. I was told probably ecu but I haven't changed it yet.

 

[vikingsven]

Haven't had a chance to test a new temp sensor, but plan to on Sunday. I'll report back.

If the new sensor doesn't work out, I am thinking about bypassing the factory temp sensor and installing a small resistor to fool the ECU into thinking a sensor is connected, similar to when I had my multi-meter attached to the sensor wiring. The hoe runs fine otherwise, so I'm not too keen on spending a bundle just to fix the gauge. My plan involves fabbing up an adapter and installing an aftermarket gauge and sender, and bolting it somewhere conspicuous on the dash console so I can keep tabs on the temps. It shouldn't be too difficult assuming the resistor hack works.

 

[hoedown]

Thanks for the reply. I wonder if there is a place that could repair those ECU's

 

[vikingsven]

I looked into that as well and found this place that looks promising. Supposedly they will repair the ECU for $790

John Deere L12 | RE532629 | RE 522527 | RE532628 | ECM

John Deere ECU Repair. L12 | RE532629 | RE522527 | RE518176 | RE532628. Your ECM will be returned fully reconditioned, tested, and ready to work.

ecmrepairusa.com

 

[mg2361]

Just so both you gentleman are aware, I have replaced many ECU's for coolant temp codes. Testing the wiring and sensor first is the prudent thing to do and sometimes that is the issue, but half the time, it is the ECU. It is a common issue with those ECU's. Just putting it out there.

 

[Honcho]

Why not to connect a sensor with a controler on a dashbord directly. I mean to install an additional controller that is conected to sensor bypassing ECU.
I did that when I insalled an additional oil preasure controler. I installed an old analog controler. that indicates a real oil preasure/ . I trust not digital ones cause they light up only when engine dead. Hello from Russia.

 

[hoedown]

mg, would you have faith in getting ECU reconditioned, or would you lean toward new?

 

[mg2361]

I have never installed anything but Deere new or Deere remanufactured ECU's, however, if that company stands behind their work, why not. The price is half of a Deere remanufactured ECU.

 

[vikingsven]

I found the repair company on Ebay as well, and they have a 100% rating, FWIW.

 

[vikingsven]

Welp, I got a chance to test a new sensor, and the issue persists. Looks like this is an ECU issue. I'm going to fiddle with adding a resistor to see if I can bypass it next, but I don't have my hopes up.
@mg2361 is it normal for the voltage out of the ecu to read randomly? On startup yesterday I measured 1.5v. Through various points during troubleshooting I read any where between .08 and 2.1v. In comparison, last week I measured 3.5 - 4.9v. Is this indicative of a failing ECU?