NAG1 Automatic Transmission

P0731-GEAR RATIO ERROR IN 1ST

For a complete wiring diagram Refer to Diagrams/Electrical Electrical Diagrams


Theory of Operation


The Transmission Control Module (TCM) constantly calculates the transmission ratio based on the input speed sensor 1 and 2 (N2-N3) signals and the calculated output shaft speed. The intent of this diagnostic is to detect if the transmission is slipping or an invalid gear ratio is present.


- When Monitored:

Engine RPM greater than 450 RPM, output speed greater than 180 RPM, no N2 - N3 input speed sensor errors present, no gear selector lever errors present, no ABS system errors, and all wheel speeds above 450 RPM.

- Set Condition:

No shifting operation and detected gear is not the actual gear. No shifting operation - detected (calculated) gear is less than actual (expected) gear, no plausible gear is calculated, actual turbine speed - calculated turbine speed is greater than 300 RPM or calculated transmission ratio is above threshold. During an Upshift - detected (calculated) gear is less than actual (expected) gear. During Downshift - detected (calculated) gear is less than actual (expected) gear.







Always perform the NAG1 Pre-Diagnostic Troubleshooting procedure before proceeding. NAG1 - Pre-Diagnostic Troubleshooting Procedure



Diagnostic Test


1. CHECK IF PINION FACTOR IS PROGRAMMED

With the scan tool, check if the pinion factor has been programmed in the FCM.


NOTE: If the Pinion Factor is not properly programmed, a Gear Ratio DTC may set.

Was the Pinion Factor properly programmed for the actual tire size and axle ratio of the vehicle?

Yes

- Go To 2

No

- With the scan tool, properly program the Pinion Factor in the FCM.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test



2. CHECK FOR OTHER TRANSMISSION DTCs

With the scan tool, check transmission DTCs

Are there any solenoid and/or solenoid supply voltage DTCs present?

Yes

- Refer to the Transmission and Drivetrain and perform the appropriate symptom(s).

No

- Go To 3



3. CHECK TRANSMISSION FLUID LEVEL

Check the transmission fluid level.

Is the fluid level correct?

Yes

- Go To 4

No

- Properly adjust the fluid level.

- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test



4. CHECK IF DTC IS CURRENT

With the scan tool, record the Environmental Data and erase Transmission DTCs.


NOTE: If the TCM detects and stores a DTC, the TCM also stores the vehicles operating conditions under which the DTC originally set and is located in scan tool under Environmental Data. Before erasing any stored DTCs, record any available data to assist in duplicating the conditions in which the DTC originally set.

Using the Environmental Data recorded earlier, test drive the vehicle while trying to duplicate the conditions in which the DTC originally set.



Did the DTC P0731-GEAR RATIO ERROR IN 1ST reset?

Yes

- Repair internal transmission as necessary.

- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test

No

- Go To 5



5. INTERMITTENT WIRING AND CONNECTORS

The conditions necessary to set this DTC are not present at this time.

Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.

Wiggle the wiring and connectors while checking for any possible open or shorted circuits.

Check for any Service Information Tune-ups or Technical Service Bulletins that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform NAG1 TRANSMISSION VERIFICATION TEST. NAG1 Transmission Verification Test

No

- Test Complete.