JLG Articulating Boom Lift 336 Fault Code: Crank Sync Noise
Also called Crank Signal Input Noise, Lift Down Valve-Open Circuit
Crank Sync Noise · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 336 (SPN 636 / FMI 2) on JLG articulating boom lifts most commonly indicates an open circuit at the lift down valve output detected by the ground module. Related descriptions for this same code also reference crank signal input noise and crank sync noise events. When set, the machine suspends lift up/down commands and limits lift speed to creep once controls are neutralized.
High severity. The machine restricts lift function to creep speed and blocks normal up/down commands until the fault is addressed, which affects productivity and could surprise an operator mid-cycle. It is not an immediate safety shutdown, but it should be diagnosed before continued lift use.
What does JLG Articulating Boom Lift error code 336 mean?
Fault code 336 covers more than one diagnostic description on JLG boom lifts. The primary body ties it to the lift down valve output circuit: the ground module monitors this circuit and sets the fault when it detects an open circuit, meaning the solenoid is not getting a complete electrical path.
A second description under the same code number relates to crank signal input noise or crank sync noise, where electrical noise or an irregular crank pattern causes multiple crank resynchronization events during a key-cycle. This triggers a warning lamp and disables adaptive fueling correction for the rest of that key-cycle.
In both cases the fault points to an electrical circuit problem rather than a mechanical failure of the valve or engine itself. The ground module's response is to protect the machine by limiting function until the circuit issue is resolved.
Common causes of 336
- Open circuit at the lift down valve output, meaning a break or disconnect somewhere in the wiring or at the solenoid connector
- Loose, corroded, or damaged connector at the lift down solenoid
- Physical damage to the wiring harness between the ground module and the solenoid
- Electrical noise or an irregular crank signal pattern causing repeated crank resynchronization events (for the crank sync noise description of this code)
How to troubleshoot JLG Articulating Boom Lift 336: first checks
- Inspect the connector at the lift down solenoid for a good, tight connection and signs of corrosion or damage
- Check continuity through the lift down valve circuit from the ground module output to the solenoid
- With the solenoid disconnected, check for an open circuit voltage of nearly 8.0 volts on the ground module output pin, this is expected for diagnostic purposes and confirms the ground module side of the circuit is functioning
- Visually inspect the full length of wiring for chafing, pinches, or physical damage, especially near boom pivot points and cable routing
- If the crank sync noise description applies, check for sources of electrical noise or interference near crank signal wiring and verify secure grounds
How the code clears
Cycle power to the machine to clear the fault after repairs are made. No further reset procedure is listed for this code beyond the power cycle. Confirm the connector is properly seated and the circuit shows continuity before returning the machine to service.
Frequently asked questions
What does JLG fault code 336 mean?
It usually means the ground module has detected an open circuit at the lift down valve output. A separate description tied to the same code number relates to crank signal noise or crank sync noise, which affects engine crank resynchronization rather than the lift valve.
Can I still operate the boom lift with fault code 336 active?
The machine will suspend normal lift up/down commands and revert to open loop current control, limiting lift speed to creep once both lift controls are returned to neutral and the machine is not enabled. This means you can still move the lift but at a restricted, slower speed until the fault is fixed.
How do I clear JLG code 336 after fixing the wiring?
Cycle power to the machine. That is the only clearing step listed for this fault, so make sure the repair is complete and continuity is confirmed before doing so.
Why would I see 8.0 volts at the solenoid connector?
With the solenoid disconnected, the ground module intentionally puts out an open circuit voltage of nearly 8.0 volts on that output pin for diagnostic purposes. Seeing this voltage with the solenoid disconnected is normal and does not indicate a problem by itself.
Is fault code 336 related to engine crank problems?
It can be. One of the descriptions tied to this code is crank signal input noise or crank sync noise, which is detected when electrical noise or an irregular crank pattern causes multiple resynchronization events. This triggers a warning lamp and disables adaptive fueling correction for the rest of that key-cycle.
What should I check first if I get code 336 on my JLG boom lift?
Start with the lift down solenoid connector and wiring. Check for a secure connection, inspect for corrosion or physical damage, and verify continuity through the circuit before assuming a more complex electrical or engine issue.