Code
P1795
VOLKSWAGEN
P — Powertrain
Vehicle Speed Signal Circuit Open
Views:
UK: 27
EN: 34
RU: 27
AI status
Completed
Completed
100%
Causes
- Open or broken wiring between speed sensor and control module
- Corroded, loose or damaged connector at sensor or module
- Failed vehicle speed sensor (wheel, transmission or gearbox sensor)
- Faulty instrument cluster/ABS/TCM receiving module
- Blown fuse or missing power/ground/reference to sensor
- Damaged reluctor/tooth ring or missing tone wheel
Symptoms
- Speedometer/odometer inoperative or erratic
- Cruise control disabled or will not set
- Transmission shift problems or default limp shifting (automatic/DSG)
- ABS, ESP or traction control warnings or degraded function
- Check Engine Light (MIL) set with P1795
- Loss of speed‑dependent features (speed limiter, adaptive systems)
What to check
- Read stored codes and freeze‑frame data with a scan tool; note simultaneous ABS/TCM/ECM codes
- Visually inspect sensor, tone wheel/reluctor and wiring harness for damage, corrosion or pinched sections
- Check fuses and module power/ground circuits related to the speed sensor
- Back‑probe sensor connector and check for reference voltage/ground per manufacturer spec
- Check for speed signal at the module connector (oscilloscope preferred) while rotating wheel or driveshaft
- Wiggle test wiring while monitoring live speed data to reproduce intermittent faults
Signal parameters
- Typical signal: digital square wave (Hall/active sensor) — ~0 V (low) to ~5 V (high) with pulses proportional to wheel/driveshaft speed
- Passive (magnetic) tone wheel: alternating AC voltage whose amplitude rises with speed; waveform sinusoidal/AC
- Expected idle/rest: 0 V (active) or no pulses; when moving, frequency increases roughly proportional to vehicle speed
- Frequency range: low hertz at walking speed up to several hundred to ~1–2 kHz at highway speeds (varies by sensor and gear ratio)
- Duty cycle approximately 40–60% for many Hall sensors; waveform should be consistent and free of dropouts
Diagnostic algorithm
- Confirm P1795 with a scan tool and note related codes and freeze frame data
- Inspect sensor, connector, wires and reluctor ring for physical damage or contamination
- Verify sensor supply: back‑probe connector and measure reference voltage and ground with ignition ON; compare to factory spec
- With vehicle safely raised and wheels supported, rotate wheel/drive component and observe speed signal at sensor connector with multimeter (AC for passive) or oscilloscope (preferred)
- If no signal at sensor but power/reference present, test continuity from sensor connector to control module pin; repair any open circuits
- If sensor shows correct output at connector but no signal at module, trace/repair wiring between sensor and module and check connector pins
- If wiring and connectors are good but no/erratic signal, replace suspect speed sensor (wheel or transmission) and recheck
- Inspect reluctor ring for missing/bent teeth or heavy rust; replace if damaged
- After repairs, clear codes and perform a road test while monitoring live speed data to confirm proper operation
Likely causes
- Wiring harness chafe or connector corrosion at sensor
- Failed speed sensor on transmission or wheel hub
- Connector pushed out or pins bent at control module or ABS unit
- Broken or missing ground or reference voltage to sensor
- Damaged reluctor ring (missing teeth, heavy corrosion)
Fault status
Status
Vehicle Speed Signal Circuit Open — the control module detects no valid vehicle speed signal. Speed‑dependent systems may be disabled until the circuit is repaired.
Repair difficulty: Medium
Diagnostic time: 1-3 hours
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