JLG Telescopic Boom Lift 34 Fault Code: Coolant Level Warning
Also called Driver Problem on a Platform Valve Block Valve Driver
Coolant Level Warning · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault 34 on JLG telescopic boom lifts (SPN 111 / FMI 1) most commonly flags a low coolant level switch input, and on platform valve block circuits it can indicate a driver problem such as a short or open circuit on basket or jib movement outputs. It is logged as a functional fault warning.
Medium severity. A low coolant warning should be treated seriously since running an engine low on coolant risks overheating and engine damage, but the machine may still be operable long enough to move to a safe stop. If the fault is instead a platform valve block driver problem, boom or jib functions tied to that circuit may not respond correctly, which affects safe operation and should be checked before continuing work.
What does JLG Telescopic Boom Lift error code 34 mean?
Fault code 34 has two distinct descriptions depending on the fault group involved: a coolant level warning, and a driver problem on a platform valve block valve driver. Both are logged under SPN 111 / FMI 1 and classified as functional fault warnings with a priority level of (6).
In the coolant level warning case, the machine's controller sees the low coolant level switch input as active, meaning the switch is telling the system that coolant is below the safe level. This is a straightforward protective warning meant to get the operator to check the cooling system before engine damage occurs.
In the platform valve block driver problem case, the fault relates to wiring or driver issues at the valve block controlling basket or jib movement (up, down, left, right). Listed problems include short to battery, short to ground, and open circuit conditions on these individual driver circuits, some of which only occur on machines equipped with electronic basket leveling.
Common causes of 34
- Low coolant level switch input has gone active, indicating the coolant level sensor detects insufficient coolant in the system.
- Faulty or failing coolant level sensor, even when coolant is actually at a proper level.
- Damaged, corroded, or disconnected cable running to the coolant level sensor.
- Short to battery on a basket or jib movement driver circuit (up, down, left, or right).
- Short to ground on a basket or jib movement driver circuit.
- Open circuit on a basket or jib movement driver circuit.
- Short to battery or open circuit specifically on machines equipped with electronic basket leveling, affecting basket up/down or platform control valve circuits.
- Short to battery, short to ground, or open circuit on the platform control valve driver itself, only on machines with electronic basket leveling.
How to troubleshoot JLG Telescopic Boom Lift 34: first checks
- Check the actual coolant level in the reservoir or radiator visually, and top off if low, only after the engine has cooled.
- Inspect the coolant level sensor and its wiring for damage, corrosion, loose connections, or disconnection.
- If the coolant level looks correct but the fault persists, suspect a faulty coolant level sensor rather than an actual low coolant condition.
- For platform valve block driver problems, inspect wiring and connectors at the valve block for the specific circuit flagged (basket up/down/left/right, jib up/down/left/right, or platform control valve).
- Check for chafed, pinched, or corroded wiring between the controller and the valve block drivers, since shorts to battery or ground and open circuits typically trace back to wiring damage or connector failure.
- If the machine has electronic basket leveling, pay particular attention to the platform control valve and basket up/down circuits, since some fault conditions are exclusive to that configuration.
How the code clears
No separate clearing step is listed for this code. Once the low coolant level is corrected or the sensor and cabling are repaired, or the wiring issue on the affected valve block driver circuit is fixed, the fault should clear on its own as the switch input or driver circuit returns to a normal state. Always verify by cycling the key or rechecking the fault display after repairs.
Frequently asked questions
What does JLG fault code 34 mean?
It depends on which fault group triggered it. Most commonly it means the low coolant level switch input is active, warning that engine coolant is below a safe level. On some machines it can also mean there is a driver problem, such as a short or open circuit, on a platform valve block circuit controlling basket or jib movement.
Is fault code 34 safe to ignore and keep working?
No. If it is a coolant warning, continuing to run the engine risks overheating and serious engine damage. If it is a platform valve block driver problem, the affected basket or jib movement may not function correctly, which is a safety concern that should be resolved before continuing to operate the lift.
My coolant level looks fine, why is fault 34 still showing?
If the reservoir level looks correct, suspect the coolant level sensor or its cable. A faulty sensor or damaged wiring can cause the switch input to read active even when coolant is actually sufficient.
Does fault code 34 always relate to coolant?
No. Fault code 34 is shared between two different fault descriptions: a coolant level warning and a platform valve block valve driver problem. The valve block version relates to wiring faults on basket or jib movement circuits, not coolant at all.
What is the platform control valve fault under code 34?
On machines equipped with electronic basket leveling, code 34 can indicate a short to battery, short to ground, or open circuit on the platform control valve driver itself, separate from the individual basket or jib movement circuits.
How do I fix a basket or jib movement fault under code 34?
Inspect the wiring and connectors for the specific circuit named in the fault, such as basket up or jib left. Look for shorts to battery or ground, or open circuits, which usually come from damaged, corroded, or disconnected wiring at the valve block.
Will fault 34 clear itself after I fix the problem?
No separate clearing procedure is listed. Once the actual coolant level, sensor, cabling, or valve block wiring issue is corrected, the fault should clear on its own. It is good practice to recheck the fault display after making repairs.