JLG Telescopic Boom Lift 43 Fault Code: Problems with the Engine
Also called Engine Coolant Temperature (ECT) Sensor Low Voltage
Problems with the Engine · ai-assisted, editor-reviewed · Last updated 2026-07-13
TL;DR
Fault code 43 on JLG telescopic boom lifts covers a group of engine-related problems, most notably a coolant temperature sensor reading a short to ground (below 0.1 volts) on Deutz-configured engines. It is also the umbrella code JLG uses for high engine temperature, low oil pressure, no alternator output, air filter bypass, fuel sensor faults, and lost ECM communication. Because it spans several engine protection circuits, treat any code 43 event as a signal to check engine temperature, oil pressure, charging voltage, and coolant sensor wiring before continuing operation.
High severity. Code 43 groups several engine protection faults, some of which (high coolant temperature, low oil pressure, no alternator output) can lead to engine damage if ignored. Treat it as a stop-and-check condition until the specific underlying fault is identified.
What does JLG Telescopic Boom Lift error code 43 mean?
JLG telescopic boom lifts use fault code 43 as a shared reporting code for a cluster of engine-related problems rather than one single failure. Depending on which sub-fault is active, it can mean the coolant temperature sensor circuit is shorted to ground, the engine is overheating, oil pressure is too low, the alternator is not charging, the air filter is clogged, the fuel level sensor circuit has a wiring fault, or the machine has lost communication with the engine's ECM.
The coolant temperature sensor low voltage condition specifically applies to Deutz-configured engines: the controller sees the coolant temperature signal reading below 0.1 volts, which it interprets as a short to ground on that sensor circuit rather than a real temperature reading.
Because this code can represent overheating, oil starvation, or loss of charging, all of which protect the engine from damage, it should never be treated as a minor nuisance code. The specific sub-fault text shown on the analyzer tells you which system actually tripped the code.
Common causes of 43
- Coolant temperature sensor circuit shorted to ground, reading below 0.1 volts (Deutz engines)
- Engine coolant temperature above 117°C (Ford engines) or above 130°C (Deutz engines), also stated as above 130°C (266°F) in later variants
- Low oil pressure: below 8 PSI (or 0.5 bar) after the engine has run for at least 10 seconds (Deutz), or a low oil pressure fault reported directly by the Ford ECM
- Oil pressure sensor shorted to battery, reading above 6.6 volts (Deutz)
- Oil pressure sensor shorted to ground, reading below 0.1 volts for more than 5 seconds, not detected during crank (Deutz)
- No alternator output: engine running 15 seconds or more with battery voltage still below 11.5 volts, or in later variants measured battery voltage below 12.5 VDC
- Air filter bypassed due to a clogged air filter
- Fuel level sensor shorted to battery, reading above 4.3 volts, or shorted to ground, reading below 0.2 volts
- Ford ECM fault codes passed through directly (all except code 63), possible during power-up
- Unrecognized Ford ECM fault code received, possible during power-up
- Loss of 485 communications with a Ford ECM for 2.5 seconds or more, possible during power-up
- Wrong engine configuration: an ECM detected on the CANBUS when the machine is configured for a non-CANBUS engine
- ECM CAN communication lost: no ECM detected when the machine is configured for a CANBUS-controlled engine, caused by lost power to the ECM or a break in the CANBUS wiring
- J1939 CANBUS engine fault reported using SPN and FMI numbers, indicating what component failed and how it failed
How to troubleshoot JLG Telescopic Boom Lift 43: first checks
- Check the analyzer's specific fault text under code 43 first, since it identifies which sub-condition (temperature, oil pressure, alternator, air filter, fuel sensor, or ECM communication) actually tripped
- Check coolant level and look for obvious overheating signs (steam, high fan noise, coolant loss) if a high engine temperature message is shown
- Check oil level and inspect the oil pressure sensor wiring and connector for corrosion or damage if a low oil pressure or oil pressure short message is shown
- Check alternator belt condition, alternator wiring, and battery connections if a no alternator output message is shown, along with actual battery voltage at idle after startup
- Inspect the coolant temperature sensor connector and wiring harness for corrosion, moisture, or a pinched/shorted wire if a coolant temperature short to ground message is shown
- Inspect the air filter and housing for clogging or a bypassed filter element if an air filter bypassed message is shown
- Check the fuel level sender wiring for a short to battery voltage or a short to ground if a fuel sensor fault message is shown
- Check the CANBUS wiring and ECM power connections if an ECM communication lost message is shown, confirming the engine configuration setting matches the actual engine installed
How the code clears
No separate clearing step is listed. Because code 43 is a shared reporting code for multiple underlying engine faults, correcting the specific condition shown in the analyzer's fault text (temperature, oil pressure, charging, air filter, fuel sensor, or ECM communication) is required before the fault will stop being reported.
Frequently asked questions
What does JLG fault code 43 mean?
It's a shared engine fault code that JLG uses to report several different problems, including coolant temperature sensor issues, high engine temperature, low oil pressure, no alternator output, a clogged air filter, fuel sensor wiring faults, and lost communication with the engine's ECM. The exact cause is shown in the analyzer's fault text, not the code number alone.
Is fault code 43 the same on every JLG boom lift?
No. The exact sub-faults and thresholds differ slightly depending on engine type (Ford or Deutz) and machine configuration. For example, high temperature is set above 117°C on Ford engines and above 130°C on Deutz engines, and some later configurations report engine temperature and alternator thresholds slightly differently.
Can I keep operating the lift with code 43 active?
It depends on which sub-fault triggered the code. If it's related to overheating, low oil pressure, or no alternator output, stop the engine and investigate before continuing, since these conditions can cause engine damage. If it's a minor sensor wiring issue, it still needs prompt attention but may not require an immediate shutdown.
What causes the coolant temperature short to ground message under code 43?
On Deutz-configured engines, this happens when the coolant temperature sensor circuit reads below 0.1 volts, which the controller interprets as a wiring short to ground rather than a valid low temperature reading. Check the sensor connector and harness for corrosion or damage.
Why does code 43 sometimes show a Ford fault code number instead?
On machines configured with a Ford engine, the JLG controller passes most Ford ECM fault codes directly through to the analyzer under code 43, except for code 63. This can also happen during the power-up sequence if the ECM reports a code before the machine finishes initializing.
What should I check first when code 43 appears with a low oil pressure message?
Check the engine oil level immediately, then inspect the oil pressure sensor and its wiring. On Deutz engines, the fault sets when pressure reads below 8 PSI (or 0.5 bar) after the engine has run for at least 10 seconds. Low oil pressure faults on Ford engines are reported directly by the Ford ECM.
Does code 43 clear itself once the problem is fixed?
No separate reset procedure is listed for this code. Since it reports several different underlying engine conditions, the fault should stop appearing once the specific issue identified in the fault text, such as overheating, low oil pressure, charging failure, or a sensor short, is corrected.