Hydraulic Oil Temperature Sensor Circuit High
The P0940 code means the vehicle's onboard diagnostic system has detected: Hydraulic Oil Temperature Sensor Circuit High. This is a moderate severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- $80 - $450 (wiring or connector at the low end; sensor replacement at the high end - diagnose before buying parts)
Read and clear transmission codes. Many trans codes are caused by low or burnt fluid -- check level and color before assuming the worst.
Basic scanners only read engine codes. This reads transmission, ABS, and airbag too.
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Common Symptoms
- Check Engine Light on
- Drivability may be normal - many circuit faults show no symptom the driver notices
- The affected system may fall back to a default strategy, costing power or economy
- Related values implausible or frozen on a scan tool
Probable Causes (Ranked by Likelihood)
- Fault in the Hydraulic Oil Temperature Sensor circuit: the signal reading above its valid range - typically a short to voltage or an open reference High
- Damaged wiring, a chafed harness, or a corroded connector at the Hydraulic Oil Temperature Sensor High
- Failed Hydraulic Oil Temperature Sensor Moderate
- Control module input/driver fault (rule this out last - it is the least common) Low
Frequently Asked Questions
What does P0940 mean?
P0940 is a generic OBD-II code defined by SAE J2012 as "Hydraulic Oil Temperature Sensor Circuit High". It means the control module detected the signal reading above its valid range - typically a short to voltage or an open reference
Can I keep driving with P0940?
Yes for normal use, but get it diagnosed - the system is running on a fallback strategy and a small wiring fault left alone tends to become a bigger one.
Does P0940 mean the same thing on every car?
Yes. P0940 is in the generic (SAE J2012) range, so the definition is standardized across manufacturers. The specific component location and repair procedure still vary by vehicle - check your service information.
Mechanics Guide Step-by-step diagnosis
Step-by-Step Diagnostic Procedure
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Read the code and freeze-frame data, then watch the Hydraulic Oil Temperature Sensor live on a scan tool.
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Inspect the connector and harness at the Hydraulic Oil Temperature Sensor before replacing anything - wiring and corrosion cause most of these.
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Back-probe the circuit and compare signal, ground, and reference voltage against the service-manual values.
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Wiggle-test the harness while watching the live value if the fault is intermittent.
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Clear the code and confirm with a road test that covers the conditions in the freeze frame.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- SAE J2012Diagnostic Trouble Code Definitions (defines the generic OBD-II code ranges)
- Cross-checked against the SAE J2012:2002 DTC table (2026-08-27)archived scan of the SAE standard — readable copy, not SAE’s current edition
Commonly Affected Vehicles
- All OBD-II vehicles - this is a generic (SAE J2012) code with the same meaning across makes
Related Codes
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