Diagnostic Test Mode Codes (Z900M and Z900R) (With Machine OFF)

This mode is used to check the integrity of the switches, sensors, wiring, and hardware of the vehicle control unit. Diagnostic information is generated in the vehicle control unit and displayed through a flashing code on the display module (next to the wrench icon).

NOTE: Do not rotate the key past RUN to START mode during these three cycles.

Before entering the Diagnostic Test Mode, it is best to turn off all switch INPUTS (i.e., brake not locked, PTO switch not in the on position, operator not in seat, etc.). Once all the INPUTS are off, the operator can enter the Diagnostic Test Mode by cycling the key switch quickly from OFF to RUN exactly three times. On the third cycle leave the key in the RUN mode.

Upon entering the Diagnostic Test Mode, the vehicle control unit will perform an automatic diagnostic check. If there are no system FAULTS and all the INPUTS are not detected, the display will flash a 1-1 Code.

See the chart below for instructions on how to remove the Fault/Input Codes in order to achieve a 1-1 Display.

Diagnostic Test Mode Code	Fault/Input Code Description	Action Needed to Remove Unwanted Codes:
3 - 7	Vehicle Control Unit’s INTERNAL Resettable Fuse Tripped	• Inspect battery, starter, and ground connections. • Inspect engine harness for pinched or chafed wires.
3 - 1	Battery Voltage High	• Inspect electrical harness for loose connections, specifically the battery positive and negative, the starter, and frame ground (on engine block).
3 - 2	Battery Voltage Low	• Check battery, starter, and ground connections. • Check charging system connections.
1 - 2	Key switch to START	Verify key switch is in RUN mode not START.
1 - 3	PTO (Knob) Switch Input ON	Turn OFF switch (knob in the down position).
1 - 4	Brake Switch Input ON	Unlock the brake pedal, check brake switch for engagement.
1 - 5	Seat Switch Input ON	De-activate seat switch (operator not in seat).
1 - 8 (Z900R)	Deck Lift Switch Input ON	Release the left lever arm button (black) switch.
1 - 9 (Z900R)	PTO Stop Switch ON	Release the right lever arm button (yellow) switch.

Diagnostic Test Mode Code	Fault/Input Code Description	Action Needed to Generate the Code:
2 - 2 (Z900R)	Engine Oil Pressure Switch ON (I.E. Closed)	Disconnect the harness connector at the oil pressure switch located on the engine.

Once the 1-1 Code has been achieved, the following steps should be performed to complete the Diagnostic Test Mode INPUT CHECKS in order to verify electrical functionality for code.

Actions Required to Verify Electrical Functionality NOTE: INPUT actions can be performed in any order.	INPUT Description	Diagnostic Test Mode
Turn the KEYSWITCH to the START position. The 1-2 Code should flash. Return to RUN position.	Key switch to START	1 - 2
Pull the knob to activate the PTO switch. The 1-3 code should flash. Return PTO to OFF position.	PTO (Knob) Switch Input ON	1 - 3
Activate the BRAKE pedal. The 1-4 code should flash. De-activate the pedal.	Brake Switch Input ON	1 - 4
Sit on seat to activate the SEAT switch. The 1-5 code will should flash. Get out of the seat.	Seat Switch Input ON	1 - 5
Push the black button on the left lever arm to activate the DECK LIFT switch. The 1-8 Code should flash. Release the button.	Deck Lift Switch Input ON	1 - 8
Push the yellow button on the right lever arm to activate the PTO STOP switch	PTO Stop Switch ON	1 - 9
Requires removal of the harness connector at the oil pressure switch on the engine. This will generate the code.	Harness connection to the oil pressure switch is working.	2 - 2

If the Diagnostic Test Mode Codes cannot be achieved when applying the INPUT Actions listed above, inspect the applicable wiring harness connections and switch, or contact your local John Deere Dealer for further assistance or part replacement.