Code
P1900
LINCOLN
P — Powertrain
Output Shaft Speed OSS Circuit Intermittent Malfunction
Views:
UK: 23
EN: 40
RU: 36
AI status
Completed
Completed
100%
Causes
- Damaged, chafed, or pinched OSS sensor wiring or connector
- Corroded or loose OSS sensor connector terminals
- Faulty OSS sensor (hall-effect or variable reluctance)
- Damaged or missing tone/reluctor ring teeth or excessive air gap
- Intermittent short to battery or ground in the OSS circuit
- Poor module ground or connector at PCM/TCM
Symptoms
- Check Engine/Transmission warning lamp illuminated
- Intermittent or erratic speedometer or incorrect vehicle speed reading
- Harsh, delayed, or erratic shifting; transmission may go into limp/limp-home mode
- Transmission diagnostic trouble codes related to OSS or speed sensor present
- Cruise control may not hold or disengage unexpectedly
What to check
- Read and record freeze-frame and failure records with a scan tool; note vehicle speed and conditions when fault set
- Check for additional transmission or vehicle codes that could point to related faults
- Visually inspect OSS sensor connector and harness for damage, corrosion, and proper routing/retention
- Wiggle test harness/connectors while monitoring OSS data on a scan tool to reproduce intermittent behavior (do this carefully)
- Inspect reluctor/tone ring at output shaft for missing or damaged teeth and proper alignment/gap
- Check for obvious water intrusion or contamination at connector and repair as needed
Signal parameters
- Hall-effect sensor: typically a three-wire circuit — 5V reference, ground, and square-wave signal from ~0V to ~5V; signal frequency rises with shaft speed
- Variable reluctance (VR) sensor: usually a two-wire AC signal; amplitude and frequency increase with speed (may be a few hundred millivolts to several volts AC depending on speed)
- At rest: OSS signal should be stable at 0V (hall) or no AC output (VR) until shaft turns
- At driving speeds: signal frequency should increase smoothly with vehicle speed without dropouts or intermittent gaps
- If intermittent: waveform will show missing pulses, voltage spikes, short drops to 0V, or noisy/smeared signal
Diagnostic algorithm
- Connect a capable scan tool and view live OSS data; attempt to reproduce the fault by performing a test drive or operating the transmission under load
- Perform a visual inspection of the OSS sensor, tone ring, harness and connectors; repair any mechanical damage or poor connections
- Backprobe the OSS connector and with the ignition on (engine off) verify reference voltage and ground (for hall sensors). Compare to known good values or service data.
- If VR-type, measure AC signal while rotating output shaft (use safe method like lifting vehicle securely and spinning driveline by wheels) or during road test; use oscilloscope for best diagnosis.
- Wiggle the wiring harness and connectors while watching live data or oscilloscope for intermittent changes (take safety precautions and avoid moving parts).
- Check continuity and resistance of sensor circuit between sensor connector and PCM/TCM connector; look for intermittent opens using a multimeter with wiggle test or dedicated continuity tool.
- Inspect and measure air gap between sensor and tone wheel per service manual; repair or replace if out of tolerance.
- If waveform is noisy or missing at sensor but present at module (or vice versa), isolate by testing at both ends to locate harness vs module problem.
- Repair or replace damaged wiring, connectors, sensor, or tone ring as confirmed by tests. After repairs, clear codes and perform a road test and re-scan to verify the intermittent fault is resolved.
- If wiring and sensor check good and intermittent readings persist, consider module connector/ground issues or intermittent TCM/PCM failure and consult dealer-level diagnostic procedures and software updates.
Likely causes
- Wiring harness abrasion near transmission or frame causing intermittent contact
- Corroded sensor/plug from road salt or moisture leading to intermittent signal
- Connector not fully seated or bent terminals producing intermittent connection
- Sensor partially failed and producing inconsistent waveform under certain speeds or temperatures
- Reluctor ring damage that only causes issues at specific shaft positions/speeds
Fault status
Status
Output Shaft Speed (OSS) Circuit — Intermittent malfunction detected. Sporadic or missing OSS signal to transmission control module affecting shift and speed functions.
Repair difficulty: Medium
Diagnostic time: 1.0-3.0 hours
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