P1780: Transmission Control System (TCS) Circuit Out of Self-Test Range
The P1780 code indicates that the Transmission Control System (TCS) circuit has failed the self-test range check. This typically means the transmission control module (TCM) has detected an electrical fault in the TCS circuit, such as an open, short, or out-of-range voltage signal. The TCS circuit is responsible for controlling shift solenoids, pressure control solenoids, and other transmission functions. This code is common in Chrysler, Dodge, Jeep, and Mitsubishi vehicles.
01. Most Common Causes
- Faulty transmission control module (TCM)
- Open or shorted wiring in the TCS circuit
- Corroded or damaged connectors
- Failed shift solenoid or pressure control solenoid
- Low transmission fluid level or dirty fluid
02. Symptoms You Will Notice
- Check Engine Light illuminated
- Transmission stuck in limp mode or fails to shift
- Harsh or delayed shifts
- Transmission slipping or overheating
- Poor fuel economy
03. Step-by-Step Diagnosis
Step 1: Scan for additional codes and note freeze frame data.
Step 2: Inspect transmission fluid level and condition; top off or replace if necessary.
Step 3: Visually check wiring and connectors for damage, corrosion, or loose connections.
Step 4: Test TCS circuit voltage and resistance with a multimeter; compare to manufacturer specs.
Step 5: If wiring is okay, test solenoids and TCM; replace as needed.
04. Commonly Affected Makes
05. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with P1780 as it can cause transmission damage or unsafe driving conditions. The vehicle may enter limp mode, limiting speed and gear selection.
How much does it cost to fix?▼
Repair costs vary from $150 to $400 depending on the cause. Simple wiring repairs may be cheaper, while replacing a TCM or solenoids can be more expensive.