JCB Dump Truck 94 Fault Code: Short Circuit At Starter Interlock Relay
Short Circuit At Starter Interlock Relay · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 94 means the TCU detected a wrong voltage at the output pin to the starter interlock relay, consistent with a short circuit to vehicle earth. It is an electrical fault in the starting circuit, not an engine or hydraulic problem.
High severity. The truck may not start or the starter interlock function may not work as intended until this is fixed. Treat it as a stop soon and diagnose issue since it affects a safety-related starting interlock circuit.
What does JCB Dump Truck error code 94 mean?
Fault code 94 is set when the TCU (transmission control unit) detects a wrong voltage at the output pin feeding the starter interlock relay. The pattern the TCU sees looks like a short circuit to vehicle earth (chassis ground), meaning the signal is being pulled low when it should not be.
The starter interlock relay is a safety and control component that prevents the starter from engaging unless certain conditions are met, such as the transmission being in a safe position. If the TCU cannot read the correct voltage on this circuit, it cannot trust the interlock relay's state, which can affect starting or safe operation of the truck.
This is a wiring and relay integrity fault rather than a mechanical or hydraulic fault. It points to a problem somewhere between the TCU and the starter interlock relay, in the cable, the connectors, or the relay itself.
Common causes of 94
- Cable running from the TCU to the starter interlock relay is defective and is contacting vehicle earth.
- Starter interlock relay has an internal defect.
- A connector pin in the circuit is connected to vehicle earth.
How to troubleshoot JCB Dump Truck 94: first checks
- Inspect the cable from the TCU to the starter interlock relay for chafing, cut insulation, or any point where bare wire could be touching a grounded metal surface.
- Check all connectors between the starter interlock relay and the TCU for corrosion, moisture, bent pins, or pins that are shorting to a ground point.
- Check the resistance of the starter interlock relay to confirm it is not internally defective.
- With the truck safely shut down and battery disconnected where appropriate, visually trace the harness routing near the relay and TCU for pinch points or rubbing against the frame.
How the code clears
No separate clearing step or reset procedure is listed for this code. Repair the wiring, connector, or relay fault identified during checks, then verify the fault does not reset after the circuit is cycled and retested.
Frequently asked questions
What does JCB fault code 94 mean on a dump truck?
It means the TCU detected a wrong voltage at the output pin going to the starter interlock relay, a pattern that looks like a short circuit to vehicle earth.
Will fault code 94 stop the truck from starting?
It can affect the starter interlock circuit, which is involved in controlling safe starting conditions. Because of that, it should be diagnosed and repaired promptly rather than ignored.
What usually causes this short circuit fault?
JCB lists three causes: a defective cable contacting vehicle earth, an internal defect in the starter interlock relay, or a connector pin that is connected to vehicle earth.
Where should I start looking for the fault?
Start by checking the cable and connectors between the TCU and the starter interlock relay for shorts to ground, then check the resistance of the relay itself to rule out an internal fault.
Is this an engine or hydraulic problem?
No. This is an electrical fault in the starter interlock wiring circuit, not related to engine mechanicals or the hydraulic system.
Is there a reset procedure after repairing the wiring?
No separate clearing step or reset procedure is listed for this code. After repairing the cable, connector, or relay, retest the circuit to confirm the fault does not return.