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Home / DTC / P0940 — Hydraulic Oil Temperature Sensor Circuit High

P0940 — Hydraulic Oil Temperature Sensor Circuit High

Detailed page for trouble code P0940.

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P0940

Generic P — Powertrain

Hydraulic Oil Temperature Sensor Circuit High

Brand: Generic
Type: P — Powertrain
Views: UK: 16 EN: 30 RU: 22
AI status
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Page language: EN

Causes

  • Open or shorted wiring in sensor circuit (short to battery/ignition voltage)
  • Faulty hydraulic oil temperature sensor
  • Poor or corroded connector or grounding at the sensor or control module
  • Failed or intermittent reference power or ground from control module
  • Actual hydraulic oil over-temperature or related thermal fault (cooler clogged, low fluid)
  • Internal control module fault or damaged sensor harness (chafing, pinched)

Symptoms

  • Transmission or hydraulic system warning lamp illuminated (CHECK TRANS/AT/PS warning)
  • Stored DTC P0940 and possibly related codes
  • Transmission may go into limp mode or reduced performance
  • Erratic shifting, harsh engagement or shift delays (if related to transmission control)
  • Visible signs of overheated hydraulic oil (burnt smell, dark oil) in severe cases
  • Intermittent or constant incorrect temperature reading on scan tool/live data

What to check

  • Read and record trouble codes and freeze frame data with a scan tool; note engine and hydraulic oil temperatures, vehicle speed and operating conditions
  • Check live data: hydraulic oil temperature sensor voltage and reported temperature while cold and after warm-up
  • Visually inspect sensor, connector and harness for damage, corrosion, melted insulation or pinched wires
  • Perform a wiggle test on the harness and connector while watching live data for intermittent changes
  • Verify hydraulic oil level and condition; check for signs of overheating (discoloration, odor)
  • Check for related DTCs (e.g., pressure, coolant or other temperature sensors) that indicate systemic overheating

Signal parameters

  • Typical sensor circuit uses a reference voltage (often 5 V) and returns 0–5 V signal; expected operating voltage depends on sensor design — check OEM spec
  • Many oil-temperature sensors are thermistors: resistance changes with temperature. Expected resistance at 20–25°C commonly falls in the kilo-ohm range; consult OEM chart for exact values
  • Look for a stable signal that changes smoothly with temperature; abrupt jumps or a fixed high voltage often indicate wiring/short faults
  • Reference voltage (if present) should be ~5 V with key ON; sensor ground should be near 0 V

Diagnostic algorithm

  1. Safety first: allow hot hydraulic components to cool before touching. Use appropriate PPE.
  2. Capture codes and live data: note stored freeze frame. Check for additional transmission/hydraulic codes.
  3. Compare hydraulic oil temperature reading from scan tool to ambient/engine temp. If reading is implausibly high immediately after cold start, suspect electrical fault.
  4. Visually inspect sensor, connector and wiring for damage, corrosion, or melted insulation. Repair any obvious problems.
  5. With ignition ON (engine off) backprobe the sensor connector: verify reference voltage (typically ~5 V) and sensor signal voltage. Record values.
  6. Check sensor ground continuity to chassis ground. Repair poor ground connections.

Likely causes

  • Sensor wiring shorted to 12 V at connector or splice
  • Faulty sensor with internal short or wrong resistance
  • Corroded/loose connector causing high reading or intermittent high voltage
  • Loss of sensor ground or damaged ground circuit causing elevated signal
  • Actual hydraulic oil overheating causing a legitimately high sensor reading

Fault status

⚠️ Status
Hydraulic oil temperature sensor circuit voltage higher than expected; control module stored P0940 and may reduce system performance or set a warning.
🟡 Repair difficulty: Medium
⏱️ Diagnostic time: 0.5-2.0 hours

Similar codes

P0118 P0117 P0119 P0181 P0191
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