Generac 1501 is a fault code on Generac standby generators. Code 1501 specifically indicates the oil pressure sensor circuit has a fault - either open circuit, short circuit, or reading out of expected range. Unlike 1505 which indicates actual low oil pressure, 1501 is a sensor circuit problem.
Here's what I tell people when they call me about this one: don't freak out about your engine. Code 1501 is an electrical problem, not a mechanical one. Your oil's probably totally fine. The controller just can't confirm that because it's lost the signal from the pressure sensor. I've seen this a dozen times this past winter alone, mostly from rodent damage and corroded connectors. Ignore it long enough and your generator won't start when the next outage hits.
Digital multimeter with continuity and ohms settings, Phillips #2 screwdriver
What Does the 1501 Code Mean?
Don't panic. This isn't your engine seizing. Code 1501 means the brain of your Generac lost contact with the oil pressure sensor circuit, not that your oil is actually low. That's code 1505. This one's an electrical fault, usually a loose connector, chewed wire, or a sensor that's finally given up. Most of the time you're looking at a $15 sensor or a quick wiring fix, not a $2,000 engine job.
Most Likely Causes
Based on aggregated repair data, here is the probability breakdown for this error code:
Oil pressure sensor wiring open circuit40%
Sensor connector corroded24%
Oil pressure sensor failed14%
Wiring chafed against engine components12%
Controller input circuit damaged10%
Symptoms You May Notice
The 1501 alarm code is showing on the Evolution controller display with the red alarm light solid on, and the unit won't run.
Generator shut down mid-run or refused to start entirely, alarm beeping, and you're standing there in the dark.
The unit kicks on during the weekly exercise cycle, runs for a few seconds, then shuts down with an alarm before completing the cycle.
You found out the generator didn't start during a recent power outage and when you checked the history log, 1501 was sitting there waiting for you.
Intermittent alarm that clears on reset but keeps coming back every few weeks, usually worse when it's wet or cold outside.
Can you reset a Generac generator to clear the 1501 code?
Switch the controller to OFF first. Press ALARM RESET to clear the active fault. Before you clear it, scroll through the history log and write down what's in there so you have a record. Then press MANUAL to attempt a restart. If 1501 comes back immediately, don't keep hammering the reset button. You've got a hard wiring fault to find first. If it starts and runs clean, let it go for 10 minutes and watch closely. A clean run means the fault was temporary, but keep an eye on it over the next few exercise cycles.
Tools Required for Diagnosis
Digital multimeter with continuity and ohms settingsPhillips #2 screwdriver10mm socket with ratchetFlathead screwdriverNeedle-nose pliersHeadlamp or flashlightElectrical contact cleaner sprayWire stripper and crimping tool (if splicing damaged wires)
Diagnostic Checklist
Follow these steps in order. We start with the easiest external fixes before opening up the machine.
ComponentComponent Under Test
Expected Range0–5 ohms
ConditionIf Open (OL) or infinite, replace component.
Frequently Asked Questions
Is Generac code 1501 serious?
Yeah, it's serious in the sense that your generator won't run with it active. The controller won't start the engine if it can't confirm oil pressure status. But here's the good news: 1501 is an electrical fault, not a mechanical failure. Your engine's probably totally fine. I've seen guys panic thinking they need a new engine when all it was is a $14 pressure switch and 20 minutes of work. Get it fixed before the next outage though, because the whole point of a standby generator is that it starts when the power goes out.
Can I reset code 1501 myself?
You can reset it, but if the underlying problem's still there it'll come right back. Press OFF, then ALARM RESET, then MANUAL. If it starts and runs clean, great. Watch it. If 1501 pops back immediately, you've got a real fault to find. Don't keep hammering the reset hoping it'll stick. That's not how it works. Find the actual problem first. Usually it's that spade terminal on the sensor connector, takes like 2 minutes to check once you know where to look.
What's the difference between code 1501 and code 1505?
People mix these up all the time so good question. Code 1505 is the scary one. That means your engine actually has low oil pressure and shut down to protect itself. Check your oil level immediately if you ever see 1505. Code 1501 is different. That means the controller can't read the sensor at all because the electrical circuit has a problem. Your oil pressure might be perfectly fine but the sensor can't report it. Think of it like your car's gas gauge breaking versus actually running out of gas. Same instrument, totally different problem.
How much does fixing a 1501 code usually cost?
If it's just the sensor, you're looking at $15-30 for the part and maybe an hour of your time. The Generac oil pressure switch is part number 0D4787 on most Evolution-equipped units. If the wiring got chewed up by rodents and you need to splice and re-route, add another hour or two of labor if you're paying a tech. Worst case where the Evolution controller board itself needs replacing, that's $350-500 in parts alone. But the board's almost never the culprit. Start with the sensor and the connector. That's where 90% of these codes end up.
Should I call a Generac dealer for this code?
Depends on your comfort level with basic electrical work. If you can use a multimeter and you're OK poking around inside a generator cabinet, this is totally a DIY fix. If 'continuity test' sounds intimidating, call a pro. Generac has certified dealers who see 1501 regularly. Just tell them upfront it's an oil pressure sensor circuit fault so they bring the right parts. A good tech should have you sorted in under 2 hours.