P0128 Fault and Temperature Gauge Failure in 2001 Oldsmobile Alero
I own a 2001 Oldsmobile Alero equipped with a 3400 engine. Recently, the vehicle triggered a P0128 diagnostic trouble code, and the temperature gauge has stopped functioning entirely. The check engine light remains on even after replacing the coolant temperature sensor. Despite this repair, both the warning light and the gauge remain non-functional. The temperature gauge does not move at all. What other components or systems should I inspect? Possible causes include a faulty thermostat, incorrect thermostat setting (should be 195°F), a stuck-open thermostat, or wiring issues—particularly on the yellow wire (which should read around 5 volts). Could there be an issue with the ECT sensor circuit or voltage supply? Any guidance on troubleshooting this combination of P0128 and temperature gauge failure would be greatly appreciated. Jeremey
P0128 indicates the Engine Coolant Temperature (ECT) sensor is not reaching the proper operating temperature.\nhttps://www.obd-codes.com/p0128\nPlease verify whether the thermostat has been removed or is functioning correctly—should be set to 195°F. Check if it's stuck open, as this can prevent proper engine warming. Also inspect the wiring: ensure there is approximately 5 volts on the red/white wire (power) and confirm voltage on the yellow wire (signal). Always use a genuine GM part; aftermarket sensors or components may not provide reliable readings or compatibility.