Engine Oil Pressure Sensor Circuit Voltage Low (SPN 100 FMI 4)
The JLG-TH-100-4 (J1939) diesel fault code means: Engine Oil Pressure Sensor Circuit Voltage Low (SPN 100 FMI 4). This is a serious severity code.
This is a standard J1939 fault, not a proprietary code. JLG-TH-100-4 is how this equipment displays SPN 100 with FMI 4 (voltage below normal or shorted low) under the SAE J1939 standard used across heavy equipment. The same SPN can appear on any J1939-compliant machine regardless of brand — so cross-referencing it against your engine maker's documentation is valid even when the equipment brand differs.
- Keep driving?
- Limited driving only
- DIY difficulty
- moderate
- Estimated cost
- Estimates only. Cleaning and reseating a connector: your time. Wiring repair at a shop: roughly $150-$500 depending on access. Oil pressure sensor: commonly $40-$150 for the part plus labour. Confirm real oil pressure mechanically before buying parts.
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What Are the Symptoms of JLG-TH-100-4?
- SPN 100 FMI 4 shown on the display or read with a diagnostic tool
- Oil pressure reading on the display drops to zero, goes blank, or reads implausibly low while the engine sounds and runs normally
- Fault sets at key-on or on start-up, before the engine has worked hard
- Fault comes and goes when the harness near the sensor is moved, or after washing the machine or working in rain
What Causes JLG-TH-100-4? (Most Likely First)
- Signal wire between the oil pressure sensor and the engine ECM shorted to ground (chafed or pinched harness) Very Likely
- Corroded, wet or loose sensor connector Likely
- Failed oil pressure sensor (internal electrical failure) Likely
- Loss of the sensor's reference supply or ground, depending on how the engine maker wired the circuit Possible
- ECM input fault (rare; rule out wiring and sensor first) Less Likely
Can I Still Drive with JLG-TH-100-4?
Limited driving only. JLG-TH-100-4 is rated serious severity. Keep trips short and get it diagnosed soon rather than waiting for symptoms to worsen.
Common Fixes by Vehicle
What techs usually find when diagnosing JLG-TH-100-4 on specific platforms — tap a platform for the fix and the exact part:
JLG G5-18A / G10-55A / G12-55A / 1644 telehandlers Moderate DIY
JLG telehandler oil pressure shutdown traces to the same root causes as boom lifts -- low oil level (top up with the engine OEM grade), worn pickup screen, or a failed pressure switch. The G5-18A and G10-55A run Deutz; G12-55A and 1644 run JLG-spec John Deere PowerTech. Always check level on level ground before condemning a sensor. Mechanical gauge in the test port confirms actual pressure if the warning persists after a level top-up.
Labor: 1-2 hoursFrequently Asked Questions
Does JLG telehandler code 100-4 mean my oil pressure is low?
No. SPN 100 FMI 4 means the oil pressure SENSOR's signal voltage is below its valid range, or the circuit is shorted low. It is a wiring, connector or sensor fault. Actual low oil pressure is a different code (SPN 100 FMI 1). The catch is that while FMI 4 is active the engine computer cannot see oil pressure at all, so check the oil level and confirm real pressure with a mechanical gauge before putting the machine back to work.
Can I keep running the machine with this code?
Only after you have confirmed the engine actually has oil pressure. The code itself does not mean the engine is damaged, but with the sensor circuit faulted the engine's low-oil-pressure protection is blind. Verify level and pressure first, then fix the circuit promptly.
What is the most common cause?
Wiring and connectors: a signal wire chafed through to ground, or a wet and corroded sensor connector. Inspect and test the circuit before replacing the sensor.
Where does this definition come from?
SPN and FMI numbers come from the SAE J1939 standard, and most engine makers use the standard failure modes, but not every maker does: Weichai's fault tables, for example, give some FMI numbers their own meanings. So the wording here is checked against the engine maker's own fault table for the Deutz TCD 2.2, which lists this pair as "Oil pressure voltage below normal or shorted to low."
Mechanics Guide Step-by-step diagnosis
How Do You Diagnose JLG-TH-100-4?
Step 1. Understand what the code says. SPN 100 is engine oil pressure; FMI 4 means the sensor's signal VOLTAGE is below the valid range, or the circuit is shorted to a low source. The engine maker's own table for the Deutz TCD 2.2 lists it as "Oil pressure voltage below normal or shorted to low." It is an electrical fault in the sensing circuit, not a measurement of low oil pressure.
Step 2. Because the ECM can no longer read oil pressure while this code is active, it cannot protect the engine from a real loss of pressure. Before running the machine again, check the oil level on the dipstick and confirm actual pressure with a mechanical gauge at the sensor port, against the engine maker's specification for your engine.
Step 3. With the key off, inspect the oil pressure sensor connector: look for water, green corrosion, pushed-back or spread terminals, and a broken locking tab. Clean and reseat it.
Step 4. Follow the harness from the sensor back toward the ECM, looking for chafing against brackets, the block or hydraulic lines, and for crushed sections. FMI 4 on a signal wire very often means that wire has rubbed through to ground.
Step 5. With the connector unplugged and the key on, measure the sensor's supply and ground at the harness side against the engine maker's wiring diagram. With the key off, check the signal wire for a short to ground and for continuity back to the ECM pin.
Step 6. If the wiring tests good, substitute a known-good sensor of the correct part number. If the code clears and stays clear, the sensor had failed.
Step 7. Clear the code and confirm it does not return, both at key-on and after the engine has warmed up. A code that returns only when the harness moves points back to the wiring.
Sources 2
This page is built from documented references. Verify against your own service info before repair work.
- Deutz TCD 2.2 L3 Engine Fault Codes table, printed in the Genie SX-135 XC Service and Repair Manual, Part No. 1263383GT, April 2023printed page 158: DTC 1022, SPN 100, FMI 4, "Oil pressure voltage below normal or shorted to low"; also DTC 1021 (SPN 100 FMI 3, voltage above normal) and DTCs 1025/1026 (SPN 100 FMI 1, low oil pressure warning and shut-off) for contrast. The table is the engine maker's; it establishes what the SPN-FMI pair means, not that a JLG display shows it.
- SAE J1939-73Application Layer: Diagnostics (defines the SPN/FMI fault-identifier framework)
Which Vehicles Commonly Get JLG-TH-100-4?
- JLG and SkyTrak telehandlers fitted with an electronically controlled (J1939) diesel engine
- Other brands' machines with the same engine report the same SPN-FMI pair
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