Part of the John Deere Repair Manuals.
This is the factory John Deere Diagnosis and Tests manual (TM4733) for the 6120, 6220, 6320, 6420 and the L-series 6120L through 6520L tractors. Unlike a repair manual, this book is built for finding the fault: it carries the diagnostic trouble codes, the observable-symptom charts, and the step-by-step system diagnostic procedures that tell you what to test and what reading to expect. It spans every major system on these tractors, including the SyncroPlus, Power Reverser, AutoPowr IVT, and PowrQuad transmissions, the hydraulics, the electrical and electronic controls, and the operator-station and HVAC systems, across 2199 pages.
What's Inside This John Deere 6120-6520L Manual
| System | Pages | Key Topics |
|---|---|---|
| General Information | How to Use the Diagnostic Procedures, Test Setup, Reference Data | |
| Diagnostic Trouble Codes | Stored Fault Codes, Code Reading, Code-Driven Diagnostic Trees | |
| Observable Symptoms | No-Start, Power Loss, Transmission, HVAC and Electrical Symptom Trees | |
| Engine | Engine Performance and Control Diagnostics, Sensors, Fuel System Tests | |
| Electrical System | Circuit Tests, Sending Units, Relays, Harness Checks | |
| Transmissions (SyncroPlus, Power Reverser, AutoPowr IVT, PowrQuad) | Transmission Control Diagnostics by Type, Shift and Clutch Tests | |
| Drive Systems | MFWD, Differential Lock, And Drive Control Diagnostics | |
| Steering and Brakes | Power Steering Pressure Tests, Brake Valve and Accumulator, Park Brake, MFWD Brake | |
| Hydraulic System | Hydraulic and Hitch Control Diagnostics, Pressure and Function Tests | |
| Operator Station and HVAC | Cab Controls, Heating and Air-Conditioning Sensors and Diagnostics | |
| Electronics | Control Units, Display and Module Diagnostics, Diagnostic-Mode Entry |
Quick Reference Specifications
| Specification | Value | Page |
|---|---|---|
| Manual type | Diagnosis and Tests (fault codes, symptoms, system diagnostics) | |
| Models covered | 6120, 6220, 6320, 6420 and 6120L, 6220L, 6320L, 6420L, 6520L | |
| Transmissions covered | SyncroPlus, Power Reverser, AutoPowr IVT, PowrQuad / PowrQuad Plus / AutoQuad | |
| Pages | 2199 | |
| Diagnostic-mode entry | Hold the Service button with the key at IGN for the required time (4s or 8s) |
John Deere 6120-6520L Common Problems This Manual Covers
Air-conditioning compressor clutch cycles on and off too frequently
Frequent clutch cycling usually traces to the refrigerant pressure sending unit, the evaporator core temperature sending unit, or the air-conditioning relay. The diagnostic procedures give the circuit tests for each sending unit and the relay so you can confirm which one is out of range before replacing it, instead of charging or swapping the compressor for a control fault.
Manual Section: Operator Station and HVACTractor will not enter diagnostic (Dia) mode
Most failures to enter Dia mode are a timing issue at the key switch rather than a dead module. Confirm the key is held at IGN and the Service button is held for the full required interval. If the sequence is correct and the mode still will not start, the manual gives the display and module checks to confirm whether the diagnostic module or its wiring is at fault.
Manual Section: ElectronicsAmbient or cab temperature sensor gives wrong or inconsistent readings
Out-of-range sensor readings are usually a circuit or connector fault rather than a bad sensor. Run the harness and sending-unit circuit test for the affected sensor, checking the connector and the wiring back to the controller. The procedure confirms whether the reading is caused by the sensor itself or by a fault in its circuit before you replace the part.
Manual Section: Electrical SystemFrequently Asked Questions
How do I enter diagnostic mode on a John Deere 6120 to 6520L?
Diagnostic mode is reached by holding the Service button with the key switch at IGN for the required time, either 4 or 8 seconds depending on the function. If the tractor will not enter Dia mode, the manual covers the exact timing and the module checks to run when the sequence does not take.
Does this manual list the diagnostic trouble codes for these tractors?
Yes. The Diagnostic Trouble Codes section is the core of TM4733. It lists the stored codes and walks the code-driven diagnostic trees, including the HVAC and sending-unit codes such as the ambient, evaporator, and refrigerant pressure circuits, so you can move from a code to the failed component.
Is this a repair manual or a diagnostic manual?
This is the Diagnosis and Tests manual. It is built to find the fault through trouble codes, observable-symptom charts, and system test procedures rather than to detail teardown and rebuild. It pairs with the separate technical (repair) manual once you have isolated the failed part.
Which transmissions does TM4733 cover?
It covers the diagnostics for all the transmission options offered on these tractors: SyncroPlus, Power Reverser, AutoPowr IVT, and the PowrQuad, PowrQuad Plus and AutoQuad units. Each has its own control diagnostics so you test against the right specification for the transmission in the machine.
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