P0730-INCORRECT GEAR RATIO

For a complete wiring diagram Refer to Section 8W

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 trying to mechanically shift into a lower gear then the TCM intends.

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.

Possible Causes

INTERNAL TRANSMISSION PROBLEM

TRANSMISSION CONTROL MODULE

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

Diagnostic Test

1. CHECK FOR INTERNAL TRANSMISSION PROBLEM

Determine if there are any Transmission mechanical problems present.
Remove the Transmission Oil Pan and inspect for excessive debris or a plugged Transmission Oil Filter. (Refer to 21 - TRANSMISSION/AUTOMATIC - NAG1/FILTER - STANDARD PROCEDURE)
Inspect valve body for foreign material, starting with 3-4 holding valve, and continuing to the other valves.

Is there any Transmission mechanical problems present?

Yes

Repair as necessary per the Service Information.
Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)

Using the schematics as a guide, check the Transmission Control Module (TCM) pins, terminals, and connectors for corrosion, damage, or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace the TCM per the Service Information. (Refer to 8 - ELECTRICAL/ELECTRONIC CONTROL MODULES/TRANSMISSION CONTROL MODULE - REMOVAL)
Perform NAG1 TRANSMISSION VERIFICATION TEST. (Refer to 21 - TRANSMISSION/TRANSAXLE/AUTOMATIC - NAG1 - STANDARD PROCEDURE)