JCB Dump Truck 93 Fault Code: Open Circuit At The Reverse Warning Alarm Relay
Open Circuit At The Reverse Warning Alarm Relay · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 93 means the TCU detected a wrong voltage at the output pin for the reverse warning alarm circuit, a signal that looks like a short circuit to battery voltage. It points to a broken connection somewhere between the TCU and the reverse alarm device.
Medium severity. This code does not stop the truck from driving or working, but it means the reverse warning alarm may not sound when the truck is backing up. That is a real safety gap for anyone working around the machine, so it should be diagnosed before the next shift, not ignored.
What does JCB Dump Truck error code 93 mean?
Fault code 93 is set when the Transmission Control Unit (TCU) reads a voltage at the output pin for the reverse warning alarm relay that does not match what it expects. The TCU sees this as looking like a short circuit to battery voltage, which typically happens when the circuit is actually open, meaning the wiring or connector has lost its normal connection.
In plain terms: the reverse alarm is the beeper or buzzer that warns people nearby when the truck is backing up. If the circuit between the TCU and the alarm device is broken, the TCU can no longer confirm the alarm is working, and it raises this fault instead of letting the alarm silently fail.
This is an electrical wiring and connector fault, not a mechanical transmission problem. The transmission and drivetrain can keep operating normally, but the reverse alarm function tied to this circuit is compromised until the open circuit is found and fixed.
Common causes of 93
- The cable running from the TCU to the reverse alarm device is defective or has no connection to the TCU.
- The reverse alarm device itself has an internal defect.
- The connector between the reverse alarm device and the TCU has no connection to the TCU.
How to troubleshoot JCB Dump Truck 93: first checks
- Visually inspect the cable routing from the TCU to the reverse alarm device for cuts, chafing, pinches, or corrosion, especially near vibration points and connectors.
- Check both connectors in the circuit, at the reverse alarm device and at the TCU, for loose pins, corrosion, bent terminals, or connectors that are not fully seated.
- Measure the resistance of the reverse alarm device itself to confirm it has not failed internally.
- With the key on and the truck in reverse, listen and check if the alarm sounds at all, which helps confirm whether the fault is in the wiring or the alarm device.
- Check for any recent work near the reverse alarm wiring, such as body repairs, dump body modifications, or pressure washing, that could have damaged or loosened the cable or connector.
How the code clears
No separate clearing procedure or reset step is listed for this code. Once the open circuit is found and repaired, whether that means fixing or replacing the cable, reseating or replacing a connector, or replacing a defective reverse alarm device, the fault should clear on its own once the TCU sees a proper voltage signal again. Confirm the alarm sounds correctly in reverse after the repair.
Frequently asked questions
What does JCB fault code 93 mean on a dump truck?
It means the TCU detected a wrong voltage at the output pin for the reverse warning alarm relay circuit, which looks like a short to battery voltage but is usually caused by an open circuit, meaning a broken cable or connector, between the TCU and the reverse alarm device.
Is it safe to keep driving the dump truck with code 93 active?
The truck can still be driven and operated, but the reverse warning alarm may not be working. Since that alarm protects people working around the truck, treat this as something to fix promptly rather than something to ignore.
What usually causes fault code 93?
JCB lists three possible causes: a defective cable with no connection to the TCU, an internal defect in the reverse alarm device itself, or a connector that has no connection to the TCU.
How do I diagnose fault code 93?
Check the cable running from the TCU to the reverse alarm device, inspect the connectors on both ends of that circuit, and check the resistance of the reverse alarm device to see if it has failed internally.
Will fixing the wiring clear the fault automatically?
No separate reset procedure is listed for this code. Once the open circuit is repaired, the TCU should stop seeing the abnormal voltage and the fault should clear during normal operation.
Could the reverse alarm itself be the problem instead of the wiring?
Yes. JCB lists an internal defect in the reverse alarm device as one of the three possible causes, so checking the resistance of the alarm device is part of the recommended diagnostic steps.