Oil Pressure Sensor Signal Voltage Below Lower Limit
What does PERKINS-100-4 mean?
The PERKINS-100-4 (Kohler RDC2) diesel fault code means: Oil Pressure Sensor Signal Voltage Below Lower Limit. This is a serious severity code.
Common Symptoms
- Panel displays fault code 100-4 and the alarm light comes on
- Generator shuts down immediately or refuses to start
- Oil pressure gauge reads zero or shows an abnormally low value even at idle
- Red shutdown lamp illuminates on the PowerWizard 1.1/2.0 controller display
- Alarm horn sounds continuously after the fault is logged
- Event log in the PowerWizard controller shows a sensor voltage fault, not necessarily a true low-oil condition
- Generator may crank but immediately trips on shutdown before building load
Probable Causes (Ranked by Likelihood)
- Wiring harness shorted to ground between the oil pressure sensor and the ECM or controller Very Likely
- Failed or internally shorted oil pressure sensor sending a zero-volt signal Very Likely
- Corroded or loose connector at the oil pressure sensor plug causing a low-resistance path to ground Likely
- Damaged wiring insulation from heat, chafing, or rodent damage creating a ground short Likely
- Failed ECM or PowerWizard controller input channel interpreting the signal incorrectly Possible
- Incorrect sensor installed (wrong resistance or voltage range for the platform) Possible
- Actual critically low oil pressure causing the sensor to rail at its lower voltage limit Less Likely
Step-by-Step Diagnostic Procedure
Before anything else, check the engine oil level with the dipstick. If oil is low, top it off to the full mark and note whether this was the real issue. Do not start the engine if oil is absent or well below the minimum mark.
Locate the oil pressure sensor on the engine block. On most Perkins 1100 and 1300 series engines it is threaded into the left or front side of the block near the oil filter. On 2200 and 2800 series engines check the workshop diagram or Perkins EST for exact location.
With the generator OFF and the battery isolator open, unplug the wiring connector from the oil pressure sensor. Set your multimeter to DC volts. Reconnect battery power without starting the engine and measure the voltage on the signal wire in the harness connector (the wire that runs back toward the ECM, not chassis ground). You should see a reference voltage typically between 4.5 V and 5.0 V. A reading near 0 V with the sensor disconnected confirms a short to ground in the wiring harness, not a failed sensor.
If voltage is correct (near 5 V) with the sensor unplugged, plug the sensor back in and measure voltage again. A drop to near 0 V confirms the sensor itself is shorted internally. Replace the oil pressure sensor. Perkins part numbers vary by series. Note the thread size (commonly 1/8 NPT or M10x1) and pressure range before ordering.
If voltage stays near 0 V even with the sensor disconnected, trace the signal wire back toward the ECM or PowerWizard controller looking for pinched insulation, burn marks, or spots where the harness contacts the block or exhaust. Repair or replace the damaged section of harness.
Inspect the sensor connector pins for green corrosion, pushed-back terminals, or moisture intrusion. Clean with electrical contact cleaner and a small brush. Apply dielectric grease before reassembling.
If the wiring and sensor both test good, connect Perkins EST (Electronic Service Tool) to the diagnostic port and read live sensor data. Compare the voltage reading in the software against your multimeter reading at the harness. A mismatch points to an ECM input channel fault. This step requires specialty tooling. Call a certified Perkins or FG Wilson technician if you reach this point.
After any repair, clear the fault code using the PowerWizard 1.1/2.0 controller menu or Perkins EST, start the engine, and verify oil pressure reads within the normal operating range (typically 250 kPa to 480 kPa at rated speed) before returning the set to AUTO mode.
Frequently Asked Questions
What does Perkins code 100-4 mean?
It means the controller measured a voltage on the oil pressure sensor signal wire that was below the lowest value the system accepts as valid. This usually means the sensor wire is shorted to ground, the sensor itself has failed internally, or there is a corroded connector. In rare cases it can mean actual oil pressure is so low the sensor is reading at the bottom of its range, so always check your oil level first.
Can my generator still run with this code?
No. The PowerWizard controller treats a 100-4 as a shutdown fault. The generator will either refuse to start or will shut itself down within seconds of cranking. This is a protective behavior. Running an engine with genuinely low oil pressure would destroy it within minutes, so the controller does not take chances when the sensor signal looks wrong.
How much does it cost to fix?
If the oil pressure sensor is the problem, parts run roughly $40 to $120 depending on the engine series, and a handy owner can swap it in under an hour. If the wiring harness is shorted, expect $20 to $80 in materials for a DIY repair. A professional technician will typically charge $200 to $600 total once you add diagnostic time and labor, and more if the ECM itself needs replacement.
Will the generator start the next time the power goes out?
Not until the fault is cleared. The PowerWizard controller will log the shutdown event and block automatic restart in AUTO mode. You need to repair the root cause, clear the code through the controller menu or Perkins EST, and confirm the sensor reads a valid voltage before the set will respond to an ATS signal during a real outage.