P1738: 3-4 Shift Malfunction Detected
The P1738 code indicates that the Transmission Control Module (TCM) or Powertrain Control Module (PCM) has detected a malfunction during the 3rd-to-4th gear shift (or vice versa). This occurs when the speed ratio between the input shaft speed sensor and output shaft speed sensor does not match the target gear ratio for 3rd or 4th gear for a calibrated period, or when a fault is detected in the 3rd/4th clutch pressure switch circuit.
01. Most Common Causes
- Low or contaminated automatic transmission fluid (ATF)
- Faulty 3rd or 4th clutch pressure switch
- Defective shift solenoid C or D
- Short, open, or corroded wiring/connectors in the pressure switch or solenoid circuits
- Faulty linear pressure control solenoid
- Internal transmission mechanical failure (clutches, valve body)
- Faulty TCM/PCM or need for reprogramming
02. Symptoms You Will Notice
- Harsh or delayed shifts between 3rd and 4th gear
- Transmission slipping or failure to shift
- Check Engine Light illuminated
- Reduced fuel economy
- Transmission stuck in 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 related to shift solenoids and pressure switches.
Test shift solenoids C and D, and the 3rd/4th clutch pressure switch for proper operation.
Perform a transmission pressure test and evaluate line pressure control solenoid.
If all electrical tests pass, suspect internal mechanical failure; consult a transmission specialist.
1. Frequently Asked Questions
Is it safe to drive?▼
No, driving with this code can cause further transmission damage and unsafe driving conditions. It is recommended to have the vehicle towed to a repair shop.
How much does it cost to fix?▼
Repair costs vary widely: from $100–$300 for a fluid change or solenoid replacement, to $1,500–$3,500+ for a transmission rebuild or replacement.