Overcrank: Engine Failed to Start After Maximum Crank Attempts

Common Symptoms

• Generator cranks several times but never fires, then shuts down with code 16 on the RDC2 controller display
• Red fault light illuminates on the panel after crank attempts stop
• Generator does not come online during a power outage even though the ATS signaled it to start
• You can hear the starter motor engaging and disengaging multiple times before the unit goes silent
• OnCue Plus monitor or Mobile Link app shows a fault alert with no utility backup power transferred
• Weekly exercise cycle starts but the engine never runs and the unit resets to fault state
• Panel buttons are unresponsive in AUTO mode after the fault; unit requires a manual reset

Probable Causes (Ranked by Likelihood)

• Low or depleted fuel supply: gas valve closed, empty LP tank, or insufficient NG line pressure below 5 inches water column Very Likely
• Weak or failed battery unable to spin the starter fast enough to reach ignition RPM Very Likely
• Faulty fuel solenoid or gas valve not opening during crank sequence Likely
• Spark plug fouled, worn, or failed so the air-fuel mixture never ignites Likely
• Choke or air-fuel mixture issue: carburetor fault, restricted air filter, or incorrect fuel-to-air ratio for LP vs NG selection Possible
• Faulty crankshaft position sensor or RPM pickup sending no speed signal to the RDC2 controller, causing it to cut crank before ignition is confirmed Possible
• Starter motor or starter solenoid mechanically failing, producing weak cranking torque Less Likely

Step-by-Step Diagnostic Procedure

1. Step 1: Check fuel first. For LP, verify the tank is above 20% full and both the main tank valve and the generator fuel shutoff valve are fully open. For NG, confirm service is active at your meter and that no other appliances are starving the line. Low pressure is the single most common cause of overcrank on Kohler RES generators.

2. Step 2: Measure battery voltage with a multimeter. With the generator OFF, a healthy 12V battery should read 12.4V or higher. Crank the engine manually and watch for voltage to drop below 9.5V during cranking. Anything below 9.5V under load means the battery cannot deliver enough current to spin the engine to ignition speed.

3. Step 3: Inspect battery cable connections at both terminals and at the chassis ground lug. Corroded or loose connections can cause the same low-voltage drop as a bad battery. Clean with a wire brush and reconnect firmly.

4. Step 4: Locate the fuel solenoid on the carburetor or gas valve assembly. When the controller initiates a start, you should hear a distinct click as the solenoid opens. If you hear cranking but no click, the solenoid may have failed or lost its 12V signal from the RDC2 controller. Verifying solenoid voltage requires a multimeter and comfort around live 12V DC circuits.

5. Step 5: Remove and inspect the spark plug or plugs. A healthy plug has a light tan or gray electrode. A black, oily, or heavily fouled plug will not ignite fuel reliably. Kohler RES engines typically use a Champion RC12YC or equivalent. Replace if in doubt; plugs are a low-cost item.

6. Step 6: Pull the air filter and check for blockage or collapse. A severely restricted filter starves the engine of air, creating a rich mixture that will not ignite cleanly during cold cranking.

7. Step 7: After correcting any obvious issues, press OFF on the RDC2 panel to clear the fault, then press AUTO to return to standby mode. Manually trigger a test run using the MANUAL button. Watch and listen to confirm the engine fires within the first two crank attempts. If it still overcranks, the fault may be in the RPM sensor, fuel delivery components, or RDC2 controller programming. At that point, call a Kohler-authorized technician.

8. Step 8: If all basics check out and the unit still will not start, do not continue cranking manually. Repeated overcranking can overheat the starter motor and damage the flywheel ring gear. Document the conditions and call for service.

Frequently Asked Questions