What Does P1909 Mean?
The transmission fluid temperature sensor circuit has an abnormal voltage reading, indicating an open circuit, short to power, or short to ground. This prevents the TCM from accurately monitoring transmission temperature for proper shift scheduling and torque converter lockup.
Common Causes
35%
Damaged or corroded transmission temperature sensor connector or wiring harness
30%
Failed transmission fluid temperature sensor
20%
Chafed or pinched wiring causing short to ground or power
10%
Corrosion or moisture intrusion in TCM connector pins
5%
Failed transmission control module (TCM)
Diagnostic Steps
1
Step 1: Inspect transmission temperature sensor connector for corrosion, bent pins, or moisture; clean and repair as needed
2
Step 2: Measure resistance of transmission temperature sensor at various temperatures and compare to manufacturer specifications
3
Step 3: Check continuity and resistance of wiring harness between sensor and TCM; look for shorts to power or ground
4
Step 4: Inspect wiring harness routing for chafing points near exhaust, frame rails, or moving components
5
Step 5: If wiring and sensor test good, test TCM power and ground circuits, then consider TCM replacement
Estimated Repair Cost
$150 - $600
Parts + labor, varies by vehicle and location
The transmission fluid temperature sensor circuit has an abnormal voltage reading, indicating an open circuit, short to power, or short to ground. This prevents the TCM from accurately monitoring transmission temperature for proper shift scheduling and torque converter lockup.
The most common cause of P1909 (Trans Temp Sensor Circuit Open or Shorted to Pwr or Gnd) is: Damaged or corroded transmission temperature sensor connector or wiring harness
Typical repair costs for P1909 range from $150 to $600, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Vehicle may default to limp mode with harsh shifts or limited gear availability. Transmission may overheat without proper temperature monitoring, potentially causing internal damage.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1909 to identify the root cause.
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Quick Info
Category
Powertrain
System
Automatic Transmission
Difficulty
Type
Manufacturer
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