JLG Telescopic Boom Lift 66 Fault Code: Problems with the CAN Bus
Also called CAN Bus
Problems with the CAN Bus · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 66 is a priority (10) CAN bus communication fault on JLG telescopic boom lifts, including the E600. It means the ground module, platform module, power module, blam module, chassis module, cylinder load pin, boom angle sensors, or UMS module have lost communication with each other over the CAN bus network, almost always traced to inter-module wiring problems.
High severity. This code shuts down normal machine communication between control modules, which can affect platform controls, boom position feedback, and safety interlocks. It should be treated as a stop-and-diagnose condition before continuing to operate the lift.
What does JLG Telescopic Boom Lift error code 66 mean?
Fault code 66 covers a family of CAN bus communication failures reported across JLG's control system modules. The CAN bus is the shared electronic network that lets the ground module, platform module, power module, chassis module, blam module, cylinder load pin, boom angle sensors, and UMS module all talk to each other. When one of these stops sending or receiving messages, the system logs a version of code 66 identifying which link failed.
In most cases listed, the platform module and ground module lose communication with each other, and this is attributed to wiring problems between those two modules. Similar module-to-module communication losses are described for the blam module, chassis module, cylinder load pin, and main boom angle sensors #1 and #2 (on 1250AJP machines), all pointing back to wiring issues on the affected circuit.
One variant is different: excessive CAN bus communication errors, which is set when the ground module detects more than 500 bus off conditions or more than 500 bus passive conditions in the current power cycle. Another variant, 48V protection tripped, occurs when the power module stops receiving acknowledgments from the platform or ground modules and the protection circuit supplying those modules trips, again usually traced to wiring at the platform or ground module.
What triggers a JLG Telescopic Boom Lift 66 code?
Most variants of code 66 are triggered simply by loss of CAN messages between two modules, with no numeric threshold given. The exception is the excessive CAN bus communication errors variant, which sets when the ground module detects more than 500 bus off conditions or more than 500 bus passive conditions within the current power cycle.
Common causes of 66
- Wiring problems between the platform module and ground module, the most commonly cited cause across variants
- Wiring problems between the blam module and ground module (machines equipped with a blam)
- Wiring problems between the chassis module and ground module (machines equipped with a chassis module)
- Wiring problems between the cylinder load pin and ground module (machines equipped with a cylinder load pin)
- Loss of CAN communications with main boom angle sensor #1 or #2 (1250AJP only)
- Excessive CAN bus errors, more than 500 bus off or bus passive conditions detected by the ground module in the current power cycle
- Wiring problems between the platform or ground module and the power module, including a tripped 48V protection circuit that supplies the platform and ground modules
- Loss of CAN bus information from the UMS module to the ground module
- A case where the power module receives from the platform module but not the ground module, described as a condition that should not be possible, suggesting a ground module or wiring fault
How to troubleshoot JLG Telescopic Boom Lift 66: first checks
- Inspect all CAN bus wiring and connectors between the platform and ground modules first, since this is the most frequently cited link in every variant of code 66
- If the machine has a blam module, chassis module, or cylinder load pin, check the wiring and connectors specific to each of those modules for corrosion, looseness, or damage
- Check connectors and wiring at the power module, since several variants point to lost acknowledgments between the power module and the platform or ground modules
- On 1250AJP machines, check wiring and connectors at main boom angle sensor #1 and #2 if the fault names either sensor
- Check UMS module wiring and connector if the fault text specifically names lost UMS sensor communications
- Look for signs of chafed, pinched, or water-intruded harness sections anywhere along the CAN bus run, since intermittent wiring faults are the common thread across all listed causes
How the code clears
No separate clearing or reset procedure is listed for this code. Once the wiring problem causing the lost CAN communication is found and repaired, the fault should stop being reported; a power cycle of the machine may be needed to confirm the modules are communicating again, especially for the excessive CAN bus errors variant which counts events per power cycle.
Affected models and serial ranges
66 appears in our records across 1 JLG Telescopic Boom Lift models. Match your machine by model and serial number.
| Model | Serial ranges |
|---|---|
| E600 | Serial range not listed in source records |
Frequently asked questions
What does JLG fault code 66 mean?
It means a CAN bus communication failure has been detected between two or more control modules on the machine, such as the platform module, ground module, power module, blam module, chassis module, cylinder load pin, boom angle sensors, or UMS module. It is almost always tied to wiring problems on the affected circuit.
Is fault code 66 safe to keep operating with?
No. Since this fault affects communication between control modules that manage platform functions, boom position, and safety interlocks, the machine should be taken out of service and diagnosed before continued operation.
Which wiring should I check first for code 66?
Start with the wiring and connectors between the platform module and ground module, since this is the most commonly cited cause across every listed variant of this fault.
Does code 66 always point to the same fault?
No. Code 66 covers several related CAN bus communication faults depending on which modules lose contact, including platform-to-ground, blam, chassis, cylinder load pin, boom angle sensor, power module, and UMS module communication losses. The fault text displayed on the analyzer identifies which specific link failed.
What triggers the excessive CAN bus communication errors variant?
This variant sets when the ground module detects more than 500 bus off conditions or more than 500 bus passive conditions during the current power cycle, rather than a simple loss of messages between two modules.
Is there a reset procedure for fault code 66?
No separate reset procedure is listed. The fix is to locate and repair the wiring problem causing the lost communication; the fault should clear once communication is restored, possibly requiring a power cycle.
Does code 66 apply to all JLG telescopic boom lifts?
It is documented for the E600 model specifically, with additional module variants such as boom angle sensor loss noted for the 1250AJP. Other telescopic boom models may report similar CAN bus faults depending on their control system configuration.