What does it mean?
P1900 is a Powertrain (engine, transmission, fuel system) fault code. It indicates: Output Shaft Speed Sensor Circuit Intermittent .
Symptoms
- Malfunction indicator lamp that comes and goes rather than staying on
- Speedometer flickers, drops to zero briefly or reads erratically
- Sudden harsh or unexpected shifts while driving
- Transmission drops into default (limp) operation and then recovers
- Cruise control cuts out; ABS or stability functions may drop out momentarily
- Torque converter clutch cycling in and out at steady speed
Likely causes
- Intermittent open in the sensor circuit from a chafed wire or a loose terminal
- Corroded or fluid-contaminated connector at the transmission case
- Sensor failing when hot and recovering as it cools
- Metal debris on the sensor tip disturbing the signal
- Damaged, dirty or loose reluctor/tone ring teeth
- Sensor bolt loose or air gap incorrect after a repair
- Harness routed too close to a high-current cable causing electrical interference
How to fix it
- Read the freeze frame data and note speed, temperature and load when the fault set
- Road-test while graphing output shaft speed against vehicle speed and look for momentary dropouts
- Wiggle-test the sensor connector and harness while monitoring the live signal
- Remove the sensor and inspect the tip and the tone ring for debris, chips and damage
- Measure sensor resistance or check its output waveform with a meter or scope
- Confirm the mounting bolt is tight and the air gap is correct
- Repair the harness or reseat terminals first; replace the sensor if dropouts persist with proven-good wiring