What Does P1879 Mean?
The transmission control module has detected a power supply issue to the Hall effect sensor(s) used to monitor transmission component positions or speeds. This sensor requires a stable reference voltage to operate correctly.
Common Causes
35%
Damaged wiring harness or corroded connectors between TCM and Hall effect sensor
30%
Faulty Hall effect sensor internal failure
20%
Transmission control module internal power supply circuit fault
15%
Blown fuse or faulty relay supplying sensor power
Diagnostic Steps
1
Step 1: Inspect transmission wiring harness and connectors for damage, corrosion, or loose connections
2
Step 2: Check power supply voltage at Hall effect sensor connector with key on, engine off (should be 5V or 12V depending on manufacturer)
3
Step 3: Test Hall effect sensor resistance and compare to manufacturer specifications
4
Step 4: Monitor sensor signal with oscilloscope or scan tool data while operating transmission through gear ranges
5
Step 5: If all sensor and wiring tests pass, test TCM power output circuit or consider TCM replacement
Estimated Repair Cost
$150 - $800
Parts + labor, varies by vehicle and location
The transmission control module has detected a power supply issue to the Hall effect sensor(s) used to monitor transmission component positions or speeds. This sensor requires a stable reference voltage to operate correctly.
The most common cause of P1879 (Transmission Automatic Hall Effect Sensor Power Circuit Failure) is: Damaged wiring harness or corroded connectors between TCM and Hall effect sensor
Typical repair costs for P1879 range from $150 to $800, depending on the vehicle, location, and whether you do it yourself or go to a shop.
May cause transmission shifting issues, limp mode activation, or incorrect gear selection. Vehicle should be drivable but may experience reduced performance.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1879 to identify the root cause.
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Quick Info
Category
Powertrain
System
Transmission Control System
Difficulty
Type
Manufacturer
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