P1791: 3-2 Downshift Solenoid Error
The P1791 code indicates a fault in the automatic transmission's shift solenoid, specifically related to the 3-2 downshift. This code is specific to Honda/Acura vehicles with electronically controlled automatic transmissions. The Transmission Control Module (TCM) detects that the commanded downshift did not complete correctly or that there is a discrepancy between the solenoid command signal and the actual hydraulic system response.
01. Most Common Causes
- Faulty 3-2 shift solenoid or solenoid resistance out of specification
- Stuck or worn shift control valve in the transmission valve body
- Low transmission fluid level or contaminated/degraded fluid
- Faulty wiring or connectors between the TCM and shift solenoid
- Outdated or damaged TCM software
- Internal transmission wear (friction discs, bands, or clutches)
02. Symptoms You Will Notice
- Harsh or delayed shifting, especially during 3-2 downshift
- Transmission slipping or failure to downshift
- Check Engine Light illuminated
- Transmission may enter limp mode
03. Step-by-Step Diagnosis
Check transmission fluid level and condition; top off or replace if necessary
Scan for additional codes and inspect wiring/connectors to the shift solenoid
Test the 3-2 shift solenoid resistance and operation per manufacturer specs
Inspect the valve body for stuck or worn shift control valves
Update or reprogram the TCM if software is outdated
Perform internal transmission inspection if other causes are ruled out
1. Frequently Asked Questions
Is it safe to drive?▼
Driving with this code is not recommended as it can cause further transmission damage. Have the vehicle diagnosed and repaired promptly.
How much does it cost to fix?▼
Repair costs typically range from $200 to $1,500 depending on the root cause, with solenoid replacement being on the lower end and internal transmission work on the higher end.