What Does P1799 Mean?
DTC P1799 indicates the output speed sensor 2 is reporting RPM values that are too high relative to what the TCM expects based on input speed and commanded gear ratio. This could indicate a sensor fault, wiring issue, or an internal transmission problem such as clutch slippage causing an apparent over-speed condition.
Safety Warning
If caused by actual internal transmission slippage, continued driving risks catastrophic transmission failure. Even if sensor-related, incorrect speed data can cause dangerous shift behavior.
Common Causes
30%
Defective output speed sensor 2 generating erratic high-frequency signals
20%
Electromagnetic interference on the OSS2 signal wire
20%
Internal transmission clutch or band slippage causing actual over-speed
15%
Damaged reluctor ring with extra teeth or debris triggering false counts
15%
Intermittent short in the sensor wiring creating false pulses
Diagnostic Steps
1
Compare output speed sensor 2 to output speed sensor 1 and the calculated vehicle speed on the scan tool; identify which sensor is reading abnormally.
2
Inspect the OSS2 wiring for routing near ignition coils, spark plug wires, or other sources of EMI; reroute if necessary.
3
Remove and inspect the sensor tip for metallic debris accumulation and clean or replace as needed.
4
Check the reluctor ring for damage, extra material buildup, or debris that could create false trigger points.
5
If sensor and wiring are good, perform a transmission stall test and monitor for clutch slippage as a mechanical cause.
Estimated Repair Cost
$150 - $2,500
Parts + labor, varies by vehicle and location
DTC P1799 indicates the output speed sensor 2 is reporting RPM values that are too high relative to what the TCM expects based on input speed and commanded gear ratio. This could indicate a sensor fault, wiring issue, or an internal transmission problem such as clutch slippage causing an apparent ov...
The most common cause of P1799 (Output Speed Sensor 2 Circ. Rpm too High) is: Defective output speed sensor 2 generating erratic high-frequency signals
Typical repair costs for P1799 range from $150 to $2,500, depending on the vehicle, location, and whether you do it yourself or go to a shop.
If caused by actual internal transmission slippage, continued driving risks catastrophic transmission failure. Even if sensor-related, incorrect speed data can cause dangerous shift behavior.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P1799 to identify the root cause.
OBDHut Mobile App
Scan codes directly from your car with the OBDHut app.
Coming Soon
Quick Info
Category
Powertrain
System
Transmission
Difficulty
Type
Manufacturer
Recommended Tools
OBD2 Scanner
A quality scan tool helps you read codes, view live data, and clear faults.
