Faulty Output Speed Sensor 2 itself, often due to internal electrical failure or contamination.; Damaged or corroded wiring harness or connector at the sensor, including chafed wires or pushed-back pins.; Metal debris or sludge buildup on the sensor tip, disturbing the magnetic signal.; Incorrect air gap between the sensor and the tone ring on the transmission output shaft.; Damaged or worn tone ring (reluctor wheel) on the output shaft, causing erratic pulses.; Internal transmission mechanical issues, such as a slipping clutch or brake, causing actual output speed to exceed expected values.; TCM software calibration issues or internal TCM faults, though less common.

DTC codes / Volkswagen codes / P1799

P1799 · VolkswagenOutput Speed Sensor 2 Circuit RPM Too High

Q: What does code P1799 mean?

Output Speed Sensor 2 Circuit RPM Too High. P1799 on Volkswagen vehicles means the transmission control module (TCM) has detected that the signal from Output Speed Sensor 2 is reporting an excessively high revolutions per minute (RPM) value, indicating a circuit or sensor fault. The TCM compares this signal against expected values from other speed sensors and flags the code when the calculated RPM exceeds a plausible threshold for the current gear and vehicle speed.

P1799 on Volkswagen vehicles means the transmission control module (TCM) has detected that the signal from Output Speed Sensor 2 is reporting an excessively high revolutions per minute (RPM) value, indicating a circuit or sensor fault. The TCM compares this signal against expected values from other speed sensors and flags the code when the calculated RPM exceeds a plausible threshold for the current gear and vehicle speed.

SystemPowertrain

Code typeVolkswagen specific

SeverityMedium

Fix difficultyIntermediate

AreaTransmission

Symptoms you may notice

Illumination of the malfunction indicator lamp (MIL) on the dashboard, often with no other noticeable symptoms.
Harsh or erratic gear shifts as the transmission enters a failsafe or limp-home mode.
The transmission may stick in a single gear or refuse to shift up or down.
A flashing or illuminated gear indicator on the instrument cluster, sometimes showing 'P' or a wrench symbol.
Speedometer fluctuation or inaccuracy if the faulty sensor also feeds the speed display.
Reduced engine power or limited vehicle speed due to torque limiting strategies.

Common causes, most likely first

Faulty Output Speed Sensor 2 itself, often due to internal electrical failure or contamination.
Damaged or corroded wiring harness or connector at the sensor, including chafed wires or pushed-back pins.
Metal debris or sludge buildup on the sensor tip, disturbing the magnetic signal.
Incorrect air gap between the sensor and the tone ring on the transmission output shaft.
Damaged or worn tone ring (reluctor wheel) on the output shaft, causing erratic pulses.
Internal transmission mechanical issues, such as a slipping clutch or brake, causing actual output speed to exceed expected values.
TCM software calibration issues or internal TCM faults, though less common.

How to diagnose and fix it

Perform a visual inspection of Output Speed Sensor 2, its connector, and wiring for damage, corrosion, or loose pins.
Check the sensor tip for metallic debris or sludge and clean it gently with a lint-free cloth.
Measure the sensor resistance and compare to Volkswagen specifications for the specific transmission; replace if out of range.
Verify the air gap between the sensor and tone ring using a feeler gauge, adjusting or replacing the sensor if incorrect.
Inspect the tone ring for cracks, missing teeth, or wear through the sensor hole; replace if damaged.
Use a scan tool to monitor live data from Output Speed Sensor 2 and compare with Output Speed Sensor 1 and engine speed to confirm erratic or high readings.
Check for technical service bulletins (TSBs) or software updates for the TCM that address false P1799 settings.

Don't overlook the tone ring and wiring

A common misdiagnosis is replacing the sensor when the real problem is a damaged tone ring or metallic debris on the sensor tip, which mimics a failed sensor.
The code can be set by a slipping transmission clutch or brake that causes actual output speed to spike, so always compare sensor data with other speed sensors before condemning the sensor.
Corroded or chafed wiring near the transmission connector is a frequent cause on higher-mileage Volkswagens, especially where the harness rubs against the engine or transmission mounts.
After replacing the sensor, the TCM may require a basic setting or adaptation reset to clear the learned values and prevent the code from returning immediately.
P1799 can sometimes be triggered by low transmission fluid level or degraded fluid, which affects the hydraulic pressure and causes speed sensor signals to exceed expected ranges.

Can I keep driving with P1799?

It is generally safe to drive the vehicle to a repair shop if the transmission still shifts reasonably and the vehicle does not enter limp mode, but avoid aggressive acceleration or heavy towing. If the transmission is stuck in a gear or the vehicle is in limp-home mode, limit driving to a short distance at low speed to prevent further damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for Volkswagen vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.