2003 Dodge Ram 1500 5.9L Engine Running Too Cold (P1281) Fault Code Diagnosis
My 2003 Dodge Ram 1500 with a 5.9L engine has recently developed a P1281 fault code, indicating the engine is running too cold for an extended period. This issue arose after two prior thermostat replacements: first during a timing chain and water pump replacement (10 months ago), and again four months ago when the thermostat became stuck open. Currently, my coolant level is at proper levels with the correct mixture and a 195°F thermostat in place. Despite replacing spark plugs and wires, fuel efficiency has dropped significantly—from 16 MPG to just 8 MPG. No additional fault codes are present. I'm trying to identify other potential causes behind this problem. Could issues such as a faulty engine coolant temperature (ECT) sensor or poor circulation be responsible? Any insights or troubleshooting steps would be greatly appreciated.
Once the vehicle reaches normal operating temperature, what temperature is your OBD2 scanner reading from the engine coolant temperature (ECT) sensor? Even without a visible fault code, a failing ECT sensor could be misreporting temperature data and triggering the P128 or P1281 code. This would explain both the cold-running condition and reduced fuel economy.