I have checked codes and tried to find online what they are…

I don't find info for a 029 MID but 039 is common for these machines.

Based on your problem, I suspect the shift handle is at fault. It is a data link connection to the ECM and has communication problems.

Here are the details of the codes for your list.

Possible causes of the 668-9 diagnostic code are listed below:

An open, short, or a poor connection in the Cat data link circuit
Excessive noise on the data link circuit
The shifter controller has failed
The machine ECM has failed. This condition is unlikely.
System Response:

This failure results in events that are logged against an ECM that cannot be explained directly. The machine ECM cannot communicate with this ECM or the ECM appears to communicate intermittently.

The possible causes of this diagnostic code are listed below:

The alternator has failed.
Intermittent connections or poor connections
Mechanical devices are loose.
The ECM has failed. This is unlikely.

The possible causes of this diagnostic code are listed:

The energize circuit of the alarm is shorted to ground.
The alarm has failed.
The ECM has failed. This is unlikely.

System Response:

When this failure occurs, the following responses occur.

The transmission will neutralize.
The action alarm will sound.

The position sensor is a PWM sensor that operates at a frequency of approximately 250 hertz. The sensor has an operating duty cycle of 10% to 90%. 10% represents the shaft position at 0 mm (0.0 inch). 90% represents the shaft position at 24 mm (0.95 inch).

The possible causes of this diagnostic code are listed below:

The signal circuit for the sensor is shorted to ground.
The sensor has failed.
The ECM has failed. This is unlikely.

OOPS, the(###) ###-####02 code is wrong, that is for a(###) ###-####02 code for the shift handle.

The 0750 is for the steering manual mode selector switch.

This diagnostic code is associated with the Switch (Steering Mode). The FMI 02 means that the ECM determined that the signal is intermittent, erratic, or incorrect. The ECM could be receiving invalid combinations from the circuit.

System Response:

An event category 1 is logged. The system will default to a two-wheel system.

Testing the shuttle shift handle normally requires CAT ET program. I have this basic testing you could do to verify the handle and not the harness is the issue.

Test Step 3. INSPECT THE HARNESS CONNECTIONS.

1. Turn the disconnect switch to the OFF position.

1. Inspect all harness connections. Make sure that the connectors are clean and tight.

1. Check the connectors for proper mating. Ensure that all the seals are present and in place.

1. Check the harness for signs of damage or abrasion.

1. Check the wires at the connector. Ensure that the wires are secured tightly into the connector. Take care not to pull the wire out of the connector.

1. Check the exposed wires at the connectors for nicks or signs of abrasion.

1. Check for moisture inside the connector.

1. Check the connectors for dirty contacts or corroded contacts.

1. Check each pin and each socket of the machine harness connectors. Ensure that the contacts are properly installed. The contacts should mate correctly when the two pieces of the connector are placed together.

Expected Result:

The machine harness connectors are tight and free of corrosion.

Results:

• OK - The machine harness connectors are tight and free of corrosion. Proceed to Test Step 4.

   

• NOT OK - The machine harness connectors are in need of repair.

  Repair: Repair the machine harness or replace the machine harness.

  Stop.

Test Step 4. CHECK FOR SHORTS TO GROUND

Table 2

Circuit Contact

Forward Input +
H731-GY J1-25

Forward Input -
G750-BU J2-59

Reverse Input +
H730-BR J1-24

Reverse Input -
G755-GY J2-60

1. The disconnect switch remains in the OFF position.

1. Disconnect the machine harness connectors from the shuttle lever and the machine ECM.

1. At the machine harness for the ECM, measure the resistance from the contacts that are provided in the table to all possible sources of ground.

Expected Result:

The resistance is greater than 5000 ohms.

Results:

• OK - The resistance is greater than 5000 ohms. The harness circuit resistance is correct. Proceed to Test Step 5.

   

• NOT OK - The resistance is less than 5000 ohms in one or more of the measurements. The machine harness has failed.

  Repair: There is a short in the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 5. CHECK FOR SHORT TO THE +BATTERY CIRCUIT

Table 3

Circuit Contact

Forward Input +
H731-GY J1-25

Forward Input -
G750-BU J2-59

Reverse Input +
H730-BR J1-24

Reverse Input -
G755-GY J2-60

1. The disconnect switch remains in the OFF position.

1. All related machine harness connectors remain disconnected.

1. At the machine harness for the ECM, measure the resistance from the contacts that are provided in the table to all possible sources of +battery.

Expected Result:

The resistance is greater than 5000 ohms.

Results:

• OK - The harness circuit resistance is correct. Proceed to Test Step 6.

   

• NOT OK - The resistance is less than 5000 ohms. The machine harness has failed.

  Repair: There is a short between the +battery circuit and the circuit with the low resistance measurement. Repair the machine harness or replace the machine harness.

  Stop.

Test Step 6. CHECK IF THE DIAGNOSTIC CODE REMAINS.

1. Inspect the contacts and clean the contacts of the harness.

1. Reconnect all harness connectors.

1. Turn the disconnect switch and the key start switch to the ON position.

1. Operate the machine.

1. Stop the machine and engage the parking brake.

1. Observe the status of the diagnostic code.

Expected Result:

The diagnostic code is no longer active. The diagnostic code is no longer present.

Results:

• OK - The diagnostic code is no longer present. The diagnostic code does not exist at this time. The initial diagnostic code was probably caused by a poor electrical connection or a short at one of the harness connectors that was disconnected and reconnected. Resume normal machine operation. Stop.

   

• NOT OK - The diagnostic code has not been corrected. The ECM may have failed.

  Repair: It is unlikely that the ECM has failed. Exit this procedure and perform this diagnostic code again. If the cause of the diagnostic code is not found, replace the ECM. See Testing and Adjusting, "Electronic Control Module (ECM) - Replace".

  Stop.

I have replaced several handles in the past and they are not cheap. However, the harness is a more common issue. I would inspect the harness where it rubs at the front just below the ECM mount and where it passes under the machine frame as these are common damage points. Exposed wires will cause interference in the data link to the shift handle and create the -688 codes.

Thank you for using JustAnswer, if you do need further help please let me know.

If you are satisfied with my service, please take a moment to provide a rating.

Thanks again, Don

CATMASTERTECH

Glad I could help.

Thanks again, Don

CATMASTERTECH