Coolant Temperature Sensor Signal Too Low
What does KOHLER-COMMAND-P0117 mean?
The KOHLER-COMMAND-P0117 (Kohler Command EFI) diesel fault code means: Coolant Temperature Sensor Signal Too Low. This is a moderate severity code.
Common Symptoms
- Engine fault indicator or LED blink code active on equipment dash
- Engine may start hard in cold weather because ECM cannot read actual coolant temperature
- Rich-running condition, black smoke from exhaust, or strong fuel smell at startup
- Engine may hunt or surge at idle because fuel trim is not calibrating correctly
- Equipment dash displays P0117 or equivalent blink count on EFI models
- Engine runs but may feel sluggish until fully warmed up
- Fuel consumption noticeably higher than normal during mowing
Probable Causes (Ranked by Likelihood)
- Coolant temperature sensor internally shorted or failed, pulling signal voltage below 0.2V Very Likely
- Signal wire from sensor to ECM shorted to ground, collapsing the reference voltage Very Likely
- Corroded or damaged sensor connector causing a low-resistance path to ground Likely
- Broken sensor ground wire creating a reference voltage collapse at the ECM input Possible
- Water or debris intrusion into the sensor connector causing a short circuit Possible
- ECM internal input circuit fault on the coolant temp signal pin Less Likely
Step-by-Step Diagnostic Procedure
Step 1. Park the mower on level ground, engage the parking brake, disconnect the spark plug wires, and let the engine cool completely before touching any sensor or wiring.
Step 2. Locate the coolant temperature sensor on the EFI engine block, typically near the cylinder head or thermostat housing. On Kohler ECV and ECV880 engines it is a two-wire sensor with a molded plastic connector.
Step 3. Unplug the sensor connector. Set your multimeter to DC volts. With the key switch in the RUN position but engine not cranking, probe the signal wire (usually the lighter-colored wire) against chassis ground. You should read approximately 4.5-5.0V reference from the ECM. If you read less than 0.5V with the sensor unplugged, the wiring or ECM is the problem, not the sensor itself.
Step 4. With the connector still unplugged, set your multimeter to resistance (Ohms). Probe from the signal wire in the harness connector to chassis ground. You should read open circuit (OL) or very high resistance. A reading below 100 ohms confirms a short to ground in the harness wiring. Trace the wire from the sensor back to the ECM looking for pinched, melted, or chafed insulation near the engine block or frame.
Step 5. Test the sensor itself. With the engine cold (room temperature, approximately 70F), disconnect the sensor and measure resistance across its two terminals. A good Kohler coolant temperature sensor should read roughly 2,000-3,000 ohms at 70F. A shorted sensor will read near zero ohms. Replace the sensor if resistance is below 200 ohms at room temperature.
Step 6. Inspect the sensor connector body and pins closely. Look for green corrosion, bent pins, or moisture inside the connector shell. Clean with electrical contact cleaner and a small wire brush if corrosion is present. Apply dielectric grease before reconnecting.
Step 7. If harness wiring and connector test good but the fault returns, reconnect the sensor, clear the code using the Kohler PCM diagnostic tool if available, run the engine to operating temperature, and recheck. If P0117 returns with a known-good sensor and clean wiring, suspect an ECM input circuit fault and contact a Kohler-authorized dealer for ECM evaluation.
Step 8. After any repair, reconnect the spark plug wires, start the engine, and confirm the fault indicator clears within one warm-up cycle. On models without a scan tool, count LED blink codes on the EFI controller to confirm no active faults remain.
Frequently Asked Questions
What does Kohler Command code P0117 mean on my commercial mower?
P0117 means the ECM is reading an abnormally low voltage on the coolant temperature sensor signal circuit. The ECM expects to see a voltage that changes with engine temperature, roughly 0.5V when hot and up to 4.5V when cold. When it sees a signal below its minimum threshold, usually caused by a shorted sensor or a wire shorted to ground, it sets P0117 and may default to a fixed fuel map that hurts performance.
Can I still mow with P0117 active on a Kohler EFI engine?
You can usually keep mowing, but the engine will not fuel correctly because the ECM cannot read actual coolant temperature. Expect hard starts when cold, possible rich running, higher fuel use, and some power loss. Running long-term in this condition can increase engine wear. Fix it before your next full mowing day if possible.
How much does it cost to fix P0117 on a Kohler EFI mower engine?
If it is just the sensor, you are looking at $25-$55 for the part and about 30 minutes of your time if you are comfortable with basic wrenching. If a shop diagnoses and replaces it, expect $80-$180 with labor. If the wiring harness is damaged or the ECM itself is faulty, costs go up to $350-$600 for ECM replacement at a dealer.
Will clearing P0117 fix the problem or will it come back?
Clearing the code without fixing the root cause will only make the fault light go away temporarily. P0117 will return within one warm-up cycle if the sensor or wiring is still shorted. Replace the faulty component first, then clear the code. If it does not return after a full run cycle, the repair is solid.