JCB Dump Truck 27 Fault Code: Short Circuit To Battery Voltage Or Open Circuit At Converter Output Temperature Sensor Input
Short Circuit To Battery Voltage Or Open Circuit At Converter Output Temperature Sensor Input · ai-assisted, editor-reviewed · Last updated 2026-07-21
TL;DR
Fault code 27 means the transmission control unit is reading a voltage that is too high on the converter output temperature sensor circuit. This points to a short to battery voltage on the signal cable, an open (disconnected) cable, an internal sensor fault, or a connector pin shorted to battery voltage or broken.
Medium severity. This is a sensor input fault, not a direct mechanical failure, but it robs the transmission control unit of a real converter output temperature reading. Running without valid temperature feedback can let the converter overheat without warning, so it should be diagnosed the same shift it appears rather than ignored.
What does JCB Dump Truck error code 27 mean?
Fault code 27 is set when the transmission control unit measures a voltage on the converter output temperature sensor input that is too high to be a real reading. The control unit interprets this as an electrical fault rather than an actual high temperature.
The converter output temperature sensor tells the TCU how hot the fluid is coming out of the torque converter. That reading feeds into how the transmission manages cooling and protects itself from overheating. When the signal is corrupted by a wiring or connector problem, the TCU loses confidence in that value.
JCB describes this fault as either a short circuit to battery voltage or an open circuit at this sensor input, meaning the underlying electrical fault can be either a wire pushing full battery voltage into the signal circuit, or a break in the circuit that lets the voltage float high.
Common causes of 27
- Cable from the TCU to the temperature sensor is defective and has come into contact with battery voltage, most often from a chafed wire touching a powered circuit.
- Cable has no connection to the TCU at all, an open circuit that lets the input read as an abnormally high voltage.
- Temperature sensor itself has an internal defect that produces an incorrect high signal.
- Connector pin is contacted to battery voltage or is broken, which can happen from corrosion, physical damage, or a backed-out pin.
How to troubleshoot JCB Dump Truck 27: first checks
- Inspect the cable routing between the TCU and the converter output temperature sensor for chafing, pinch points, or contact with any wire carrying battery voltage.
- Check all connectors in that circuit for corrosion, bent or backed-out pins, and broken or loose terminals.
- With the connector disconnected, check the sensor cable for continuity end to end to rule out an open circuit.
- Test the temperature sensor itself for an internal short or open condition, replacing it if it fails.
- Verify the connector pin assigned to this signal is not shorted to a battery voltage source elsewhere in the harness.
How the code clears
No separate clearing step or reset procedure is listed for this code. Once the wiring, connector, or sensor fault is repaired and the input reads a normal voltage, the fault should clear on its own after a power cycle or the next diagnostic scan.
Frequently asked questions
What does JCB fault code 27 mean on a dump truck?
It means the transmission control unit sees too high a voltage on the converter output temperature sensor input. JCB lists the cause as either a short to battery voltage or an open circuit on that sensor's wiring.
Can I keep driving with fault code 27 active?
You can typically keep operating short term since this is a sensor circuit fault rather than a direct converter failure, but you lose the TCU's ability to properly monitor converter output temperature, so get it checked as soon as practical to avoid unmonitored overheating.
What is the difference between fault code 27 and fault code 25?
Code 25 covers the same type of short to battery voltage or open circuit fault, but on the transmission sump temperature sensor input instead. Code 27 is specific to the converter output temperature sensor circuit. If your symptom involves the sump temperature reading instead of converter output, check code 25 instead.
How do I check for a short to battery voltage on this sensor circuit?
With the key off and the sensor connector disconnected, check for voltage present on the signal wire. Any voltage reading there when nothing should be powering it suggests the wire has become shorted to a battery voltage source elsewhere in the harness.
Is the temperature sensor itself likely to be bad, or is it usually the wiring?
JCB lists both possibilities. Start with the cable and connectors since chafed wiring and corroded or broken pins are common and easy to inspect, then test the sensor itself if the wiring checks out clean.
Will replacing the connector or cable clear the fault automatically?
No separate reset procedure is listed. Once the short or open circuit is repaired and the TCU reads a normal voltage on the input, the fault should clear on its own without a manual reset.