Transmission Control Module (TCM) - 8HP45

P1731-INCORRECT GEAR ENGAGED

For a complete wiring diagram Refer to the Wiring Information.

Theory of Operation

The Transmission Control Module (TCM) constantly calculates the transmission ratio based on the Input Speed Sensor (ISS) and Output Shaft Speed (OSS). The intent of this diagnostic is to detect if the transmission is trying to mechanically shift into a different gear than which the TCM commanded.

- When Monitored:
Engine rpm is greater than 450 rpm, no input speed sensor DTCs present, no gear selector lever DTCs present, no ABS system DTCs and vehicle speed above 10 Km/h (6 mph).

- Set Condition:
No shift operation and actual gear differs from the target gear. No shift operation - actual (calculated) gear differs from target (expected) gear, actual (calculated) turbine speed is greater than 300 rpm or calculated transmission ratio is above calibrated threshold. During an Upshift - actual (calculated) gear is less than target (expected) gear. During Downshift - actual (calculated) gear is greater than target (expected) gear. Exception: Actual (calculated) gear is 1st and target (desired) gear is 2nd.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. 8HP45 Pre-Diagnostic Troubleshooting Procedure

1. CHECK IF ABS DTCS ARE PRESENT
1. With the scan tool, check for ABS DTCs.

Are any ABS DTCs present?

Yes

- Testing and Inspection Perform the appropriate repair.

No

- Go to 2

2. CHECK IF TRANSMISSION SOLENOID DTCS ARE PRESENT
1. With the scan tool, check for other transmission DTCs.

Are any transmission solenoid, speed sensor and/or any other transmission electrical related DTCs present?

Yes

- Testing and Inspection Perform the appropriate repair.

No

- Go to 3

3. CHECK TRANSMISSION FLUID LEVEL

NOTE: Low fluid level can be the cause of many transmission problems. Visually inspect the transmission and cooler lines for leakage and repair as necessary and adjust the fluid level. If no visual leaks are observed and the vehicle has obtained over 1610 km (1000 miles) from new or transmission service, a fluid level check is unnecessary.

1. Check the transmission fluid level and condition.

Is the fluid level correct?

Yes

- Go to 4

No

- Correct the fluid level. 8HP45 Automatic Transmission
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests

4. CHECK ENVIRONMENTAL DATA
1. With the scan tool, check environmental data for P1731.

Did the environmental data show the code setting during a 3-4 upshift or 4-3 downshift?

Yes

- Replace and program the TCMA. Valve Body - Removal.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests

No

- Go to 5

5. CHECK FOR INTERNAL TRANSMISSION PROBLEM
1. Check for an internal transmission mechanical problems.
2. Remove the transmission oil pan and inspect for excessive debris or a plugged transmission oil filter.
3. Inspect the valve body for foreign material.
4. This DTC is usually set due to an internal transmission problem such as but not limited to: stuck solenoid valve and/or contamination in the valve body, broken springs, leaking clutch seals, dislodged or broken snap ring etc.
5. Check Service Information for the appropriate service procedure and any other possible causes.

Were any problems found?

Yes

- Repair as necessary.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests

No

- Using the schematics as a guide, check the Transmission Control Module A (TCMA) terminals for corrosion, damage or terminal push out. Pay particular attention to all power and ground circuits. If no problems are found, replace and program the TCMA. Valve Body - Removal.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests