Throttle Position Sensor Voltage Too High
The KOHLER-COMMAND-P0123 (Kohler Command) diesel fault code means: Throttle Position Sensor Voltage Too High. This is a serious severity code.
- Keep driving?
- Yes, but fix soon
- DIY difficulty
- moderate
- Estimated cost
- DIY sensor replacement $45-$90 for the TPS part. Pro diagnosis and repair $120-$280 depending on whether the fault is a sensor, harness repair, or ECU issue.
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Common Symptoms
- Engine runs rough or surges at mid to high throttle positions
- Mower goes into reduced power or derate mode and will not reach full RPM
- EFI fault light on the equipment dash illuminates or blinks a fault sequence
- Engine may start but stumble or hesitate when the throttle is advanced
- Fuel consumption feels higher than normal for the workload
- Equipment may shut down under heavy cutting load
- Kohler PCM diagnostic tool shows active fault P0123 in the fault log
Probable Causes (Ranked by Likelihood)
- TPS signal wire shorted to 5V reference or 12V supply inside the harness Very Likely
- Throttle position sensor internally failed with signal pin stuck high Very Likely
- Damaged or corroded connector at the TPS causing a false high-voltage reading Likely
- ECU reference voltage circuit fault supplying more than 5V to the sensor Possible
- Chafed wiring between the TPS and ECU contacting a power wire or frame ground path reversed Possible
- Water or debris intrusion into the TPS connector causing a bridged circuit Less Likely
- Faulty ECU misreading a normal TPS signal as out of range Less Likely
Step-by-Step Diagnostic Procedure
Start with the engine OFF and key in the RUN position. Using a multimeter set to DC volts, backprobe the TPS signal wire at the sensor connector. Normal TPS signal voltage at idle closed-throttle should read between 0.5V and 1.0V. A reading above 4.5V with the throttle closed confirms the fault is live.
Check the TPS reference voltage. Backprobe the 5V reference wire at the TPS connector with the key ON, engine OFF. You should read 4.75V to 5.25V. A reading above 5.5V points to an ECU reference circuit problem rather than the sensor itself.
Unplug the TPS connector completely with the key ON. Measure the signal wire voltage at the harness side. If voltage drops to 0V or near zero with the sensor disconnected, the sensor itself is shorted internally. If voltage stays high, the short is in the wiring harness.
Visually inspect the entire TPS wiring harness from the sensor back to the ECU. Look for chafed insulation against engine sheet metal, melted spots near the exhaust, or pinched wires under a cover panel. Repair any damaged sections with solder and heat-shrink, not bare wire nuts.
Inspect the TPS connector pins for corrosion, spread pins, or moisture. Clean with electrical contact cleaner and a pin cleaning brush. Apply dielectric grease to the connector before reassembly.
If the harness checks out clean and the sensor still reads high, replace the TPS. Kohler EFI engines use a three-wire Hall-effect or potentiometer-style TPS. After replacement, connect the Kohler PCM diagnostic tool to verify the new sensor reads 0.5V to 1.0V at closed throttle and climbs smoothly to 4.0V to 4.5V at wide open throttle.
Clear the P0123 fault with the Kohler PCM diagnostic tool after repairs. Run the engine through a full throttle sweep and confirm the fault does not return. If P0123 comes back immediately after replacing a known-good sensor, suspect the ECU reference voltage circuit and contact a Kohler-authorized dealer for ECU diagnosis.
Frequently Asked Questions
What does Kohler Command code P0123 mean on my commercial mower?
P0123 means the ECU detected a voltage signal from the throttle position sensor that is higher than the expected range. The ECU expects a signal between roughly 0.5V and 4.5V depending on throttle position. When that signal reads above the maximum threshold, the ECU cannot trust throttle position data and may derate engine power to protect the machine.
Can I keep mowing with a P0123 code active?
You can finish a job in a pinch, but the engine is likely running in a derate or limp mode that limits RPM and power. Pushing hard cutting conditions with this fault risks a mid-job shutdown and could stress the engine if the ECU is commanding incorrect fueling based on a bad throttle signal. Fix it before the next full workday.
How much does it cost to fix P0123 on a Kohler EFI engine?
If the TPS itself is the problem, the sensor runs $45 to $90 in parts and you can swap it yourself in under an hour with basic tools, putting DIY cost under $100. If the fault turns out to be a wiring harness repair, add an hour of labor at a dealer, typically $120 to $180 all in. An ECU fault is rare but the most expensive path, potentially $250 to $400 at a Kohler-authorized shop.
Will P0123 clear itself if I just restart the engine?
The fault light may go out temporarily on a cold restart, but if the sensor or wiring fault is still present the code will come back within seconds or minutes of running. You need to repair the root cause and then clear the code with the Kohler PCM diagnostic tool for a confirmed clean bill of health.