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Discussion Starter · #1 ·
I am having an issue with a late 7520 (made around 2006) with a Power Quad transmission.

It has been having intermittent shutdown issues for the last several years where it would die and then be able to be restarted. Now it has died and only restarted once in the last week after multiple attempts.

It usually chokes 2 times while putting out 2 puffs of black smoke and dies.

While investigating this issue, I have noticed that the ECU is not connecting to the BCU except for the last time it started for 10 minutes. You can cycle through all the computers on the dash screen but the ECU doesn't show up until it intermittently decides to run.

I confirmed power on F04/1, F04/2 and F04/9 at the fuse box and at the ECU connectors A2, H1, K1. I checked the CAN diode and found it to be good.

I checked the roof wiring harness by taking off the roof cap. It appeared to be in good condition.

I inspected the ECU male pins and they appeared to be in good condition. The ECU plug was not loose when taken apart for inspection. The ECU harness appeared to be in good condition.

The wiring harness from the ECU to the Stanadyne Electronic injection pump was changed out by a John Deere tech last year and appears to be in good condition.

I changed out the passive terminator in the upper front right corner of the cab roof as well as the active terminator under the right hand shift console.

I checked the main wiring harness where it goes around the corner in the right rear of the cab as that is a known rubbing point. I found 4 wires rubbed down to copper and repaired them as well as wrapping the harnesses with rubber where they go around the corner.

I have checked the fuel injection system. The injection pump is getting good fuel supply from the electric lift pump. The injectors are getting a small pulse of fuel when cranking but will only fire when commanded by the ECU.

The tractor runs really good when it runs...

Fault Codes from when it DOESN'T start:
BCU 302086.31 FWD Clutch Solenoid Valve Circuit Fault
BCU 000639.14 CAN Bus Very High Error Rate
BCU 302131.31 Turn Signal Circuit Fault

EPC 306121.09active ECU/BCU No Data (Engine Speed)
EPC 306060.31 ECU/BCU No Data (Engine Speed)
EPC 306057.31 Transmission Enable Signal Faulty
EPC 306120.09 BCU No Data Transmission Output Speed

BIF 000110.16 Coolant Temp High
BIF 000110.00 Coolant Temp Very High
BIF 000177.16 Transmission Oil Temp High
BIF 000100.00 Engine Oil Pressure Low
BIF 000190.02 No Signal Engine Speed Sensor
BIF 000127.00 Transmission Oil Pressure Low
BIF 000126.16 Transmission/Hydraulic Filter Clogged
BIF 000639.02 CAN Bus Open Circuit
BIF 000186.16 Warning Rear PTO Speed

SIC 334003.09 TCU or BIF Not Sending Data (Hydraulic Oil Temp)
SIC 334002.09 BCU Not Sending Data (Engine Hours)
SIC 000639.14 CAN Bus Error Rate High
SIC 334001.09active ECU/BCU Not Sending Data (Engine Speed)


Fault Codes from when it DOES start:
BCU 302131.31 Turn Signal Circuit Fault

At this point, I have more terminators ordered and am planning to replace all the terminators on the tractor.

I have an engine speed sensor coming to throw on because they're cheap.

I'm planning to clean all the grounds I can find...if anyone can point me to all the ground locations, that would be great.

Any thoughts or help would be appreciated as this is our only tractor capable of running our haying equipment.
 

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Discussion Starter · #2 ·
Update: Replaced 3 terminators with new units from John Deere. Cleaned the grounds...there's quite a few.
No change yet.
Haven't received the engine speed sensor yet but will install when it comes.
John Deere tech is coming out today to see if they can find the problem.
 

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Discussion Starter · #3 ·
Update: John Deere tech came today and checked over the tractor. He believes the issue to be ECU related as he was unable to communicate with the ECU using Service Advisor but all the other computers/controllers were responding. He checked power and ground at the ECU plug and found that to be good. He also checked the Computer Access Network at the ECU plug and found that to be good. He attempted to re-flash the ECU but the connection just timed out.

So the ECU is receiving power and data but not responding.

I told him to order up an ECU and install it so hopefully that will take care of the issue.
 

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Discussion Starter · #4 ·
Update: John Deere tech came and installed a new L12 ECU (Engine Control Unit), flashed it with the correct torque file and the tractor started right up and has been running good.

I hope this thread may be helpful to someone in the future.
Kind Regards,
Josiah
 

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Thanks for update. I'm glad I can start my ole '91 JD 4255 then disconnect batteries & drive it. Granted the warning lights & AC won't operate but I could use it!
 
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