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DTC codes / Ford codes / P1900

P1900 · FordOutput Shaft Speed OSS Circuit Intermittent Malfunction

P1900 on a Ford means the powertrain control module (PCM) has detected an intermittent fault in the output shaft speed (OSS) sensor circuit, which measures transmission output speed. The PCM sets this code when the OSS signal drops out or becomes erratic for a brief period, often without storing a hard failure.

SystemPowertrain
Code typeFord specific
SeverityMedium
Fix difficultyIntermediate
AreaTransmission

Symptoms you may notice

  • Illumination of the check engine light or transmission warning light, often with no other symptoms.
  • Intermittent harsh or delayed shifting, especially when the signal drops out momentarily.
  • Speedometer needle fluctuation or erratic readings if the OSS signal is used for vehicle speed.
  • Transmission may enter limp mode (stuck in a single gear) during the intermittent fault.
  • Poor fuel economy or unusual engine RPM fluctuations during steady driving.

Common causes, most likely first

  1. Damaged or chafed wiring in the OSS sensor circuit, often near the transmission or exhaust.
  2. Corroded or loose electrical connector at the OSS sensor or PCM.
  3. Faulty OSS sensor itself, producing an intermittent signal due to heat or vibration.
  4. Metal debris or damage on the output shaft speed sensor reluctor wheel or tone ring.
  5. Internal transmission mechanical issues causing erratic reluctor wheel movement.
  6. PCM software glitch or internal fault in the OSS signal processing circuit.

How to diagnose and fix it

  1. Inspect the OSS sensor connector and wiring for corrosion, chafing, or loose pins; repair as needed.
  2. Check the OSS sensor resistance and signal output with a multimeter or oscilloscope while wiggling the harness.
  3. Remove and inspect the OSS sensor for metal debris or damage; clean or replace if necessary.
  4. Inspect the reluctor wheel or tone ring on the output shaft for damage or debris through the sensor hole.
  5. Perform a wiggle test on the wiring harness from the OSS sensor to the PCM while monitoring live OSS data.
  6. If wiring and sensor are good, check for intermittent PCM connection issues or software updates.
  7. Clear the code and road test under various conditions to confirm the repair.

Intermittent OSS faults often hide in the harness

  • A common misdiagnosis is replacing the OSS sensor when the real problem is a chafed wire near the exhaust manifold or a corroded connector pin.
  • The OSS signal can drop out only at certain temperatures or road speeds, so a static resistance check may pass while the fault is still present.
  • On some Ford models, the OSS sensor shares a ground with other sensors, so a bad ground can cause intermittent OSS codes along with other drivability symptoms.
  • P1900 can be set by a momentary loss of signal that does not trigger a limp mode, leading owners to ignore it until a hard failure occurs.
  • Aftermarket transmission work or a recent clutch replacement can disturb the OSS sensor or reluctor wheel, causing this code to appear shortly afterward.

Can I keep driving with P1900?

You can usually continue driving with P1900, but avoid aggressive acceleration or heavy towing until the intermittent fault is repaired, as a sudden loss of OSS signal can cause harsh shifting or limp mode.

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 Ford vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.

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