Basic checks
Veepeak OBDCheck BLE
A Bluetooth LE adapter for reading standard engine codes and supported live data.
View on AmazonP0939
Hydraulic Pump Relay Control Circuit High
Moderate severity
The hydraulic oil temperature sensor reports a circuit low fault. Oil temperature feedback for hydraulic system is unreliable.
The hydraulic oil temperature sensor reports a circuit low fault. Oil temperature feedback for hydraulic system is unreliable.
Common causes
- high
Temperature sensor failed
One of the most commonly reported causes for this code — check this first.
Typical part cost: $70-330
- medium
Wiring fault
A plausible cause — test and verify before replacing parts.
Typical part cost: $70-330
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First things to check
- 1Confirm the code with a scan tool and check for additional related codes.
- 2Inspect the relevant sensors, wiring, and connectors for damage or corrosion.
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Tools you may need
Already have a compatible scanner? Use it. If not, a Bluetooth OBD2 adapter can help you confirm engine codes and check supported live sensor data before replacing parts.
Regular diagnostics
vgate iCar Pro BLE 4.0
A Bluetooth LE adapter with an automatic sleep feature for routine code and sensor checks.
View on AmazonAnother option
OBDLink CX
A Bluetooth LE adapter to consider when comparing supported vehicles and diagnostic apps.
View on AmazonIllustrations shown, not product photos. Check vehicle, phone and app compatibility before buying. These adapters do not guarantee access to ABS, airbags or manufacturer-specific systems. Clearing a code does not repair the fault and can reset emissions readiness monitors.
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Related codes
See related trouble codes
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Frequently asked questions
What does P0939 mean?
P0939 means "Hydraulic Pump Relay Control Circuit High". It is a generic OBD-II code that points to a fault in the transmission / hybrid-ev control.
What are the most common causes of P0939?
temperature sensor failed; wiring fault; connector pins corroded - high contact resistance — these are the most commonly reported causes. Verify with a proper diagnosis before replacing parts, or use the Wrenchify app for a vehicle-specific diagnosis.
Can I keep driving with this code?
The vehicle is usually drivable for short distances, but the problem can worsen or affect emissions. Diagnose and repair as soon as practical. Use the Wrenchify app for a full diagnosis specific to your vehicle.
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