Coolant Temperature Sensor Signal Voltage Too High

Common Symptoms

• Controller displays fault code 110-3 on the panel screen
• Yellow or red alarm LED illuminates on the generator control panel
• Generator may crank but shut down shortly after starting
• Coolant temperature gauge reads maximum or pegged high even on a cold engine
• Generator logs the fault and may refuse to auto-start during a power outage
• No actual overheating observed, engine and radiator feel normal to the touch
• Weekly exercise cycle starts but trips on alarm before completing

Probable Causes (Ranked by Likelihood)

• Coolant temperature sensor has failed open circuit internally, causing signal wire to float high Very Likely
• Wiring harness connector at the sensor is corroded, loose, or has backed-out pin causing open circuit Very Likely
• Signal wire between sensor and ECM is chafed, broken, or disconnected at an intermediate connector Likely
• Coolant temperature sensor has drifted out of specification and no longer reads within the expected voltage range Likely
• ECM or controller input circuit has failed, reading voltage high on that channel regardless of sensor output Possible
• Water or moisture intrusion into the sensor connector causing corrosion that lifts signal voltage Possible
• Wrong replacement sensor installed with incorrect resistance curve, pushing output outside ECM accepted range Less Likely

Step-by-Step Diagnostic Procedure

1. Step 1. Safety first. Press the STOP button on the control panel and confirm the generator is not running. Open the generator housing and locate the coolant temperature sensor. On most Perkins 1100, 1300, and 1700 series engines it threads into the thermostat housing or cylinder head and has a single-wire or two-wire connector.

2. Step 2. Inspect the sensor connector visually before touching anything. Look for green or white corrosion on the pins, cracked connector body, or a pin that has backed out of the plug housing. A corroded or loose connector here is the single most common cause of a 110-3 fault.

3. Step 3. Disconnect the sensor connector. Set your multimeter to DC voltage. With the key switch in the RUN position but engine not cranking, probe the signal wire (usually the wire that is NOT chassis ground) against a known good chassis ground. You should read roughly 5 volts DC, which is the ECM reference voltage with no sensor attached. If you read 0 volts, there is a break in the wire between sensor and ECM rather than an open at the sensor itself.

4. Step 4. Set your multimeter to resistance (Ohms). Probe across the two terminals of the sensor itself (sensor disconnected from harness). At a cold engine, roughly 20 degrees C or 68 degrees F, a good Perkins coolant temperature sensor typically reads between 2,000 and 3,000 Ohms. A reading of OL (overload or infinite resistance) confirms the sensor has failed open and must be replaced. Consult your specific engine parts manual for the exact resistance table.

5. Step 5. If the sensor resistance reads within spec, reconnect the sensor and check the harness continuity. Disconnect both ends of the signal wire at the sensor connector and at the ECM harness connector. Set multimeter to continuity or resistance mode and check end to end. Any reading above 1 Ohm on that wire suggests a break or high-resistance chafe point in the harness.

6. Step 6. Inspect the grounding circuit. A poor chassis ground on the engine block can cause sensor reference voltages to shift high and generate false 110-3 faults. Find the main engine ground strap, check that both ends are clean and tight, and measure resistance from engine block to battery negative. It should be less than 0.1 Ohms.

7. Step 7. If sensor and wiring both test good, this step requires the Perkins EST Electronic Service Tool or PowerWizard 1.1/2.0 controller diagnostics to read live sensor data and confirm whether the ECM input channel itself is at fault. At that point, contact a certified Perkins or FG Wilson service dealer before replacing the ECM.

8. Step 8. After replacing the sensor or repairing the harness, clear the fault using the controller reset procedure (refer to your PowerWizard or DSE controller manual), then put the unit back into AUTO and run a manual exercise cycle. Confirm the coolant temperature reading climbs gradually from ambient to normal operating range of roughly 80 to 95 degrees C as the engine warms up.

Frequently Asked Questions