Cause
Thermostat stuck open
A thermostat that never closes, so the engine takes far too long to warm up and may never reach operating temperature in cold weather. The module keeps the mixture rich until it sees normal coolant temperature, so the consequences are poor economy, extra emissions and a heater that never gets hot — with no warning light, because nothing is overheating.
Typically a moderate job.
Codes this can cause (29)
Codes where this is a likely explanation first, rather than merely a possible one.
- P00B2 Radiator Coolant Temperature Sensor Circuit Range/Performance Likely for this code Moderate
- P0116 Engine Coolant Temperature Sensor 1 Circuit Range/Performance Likely for this code Moderate
- P011B Engine Coolant Temperature/Intake Air Temperature Correlation Likely for this code Moderate
- P0125 Insufficient Coolant Temperature for Closed Loop Fuel Control Likely for this code Moderate
- P0126 Insufficient Coolant Temperature for Stable Operation Likely for this code Moderate
- P0128 Coolant Thermostat — Temperature Below Regulating Point Likely for this code Moderate
- P015E Excessive Time to Enter Closed Loop Fuel Timing Control Likely for this code Moderate
- P016A Excessive Time To Enter Closed Loop Air/Fuel Ratio Control Likely for this code Moderate
- P050E Cold Start Engine Exhaust Temperature Too Low Likely for this code Moderate
- P2181 Cooling System Performance Likely for this code Moderate
- P2183 Engine Coolant Temperature Sensor 2 Circuit Range/Performance Likely for this code Moderate
- P2A3F Excessive Time to Enter Alternative Fuel Control Likely for this code Moderate
- P0196 Engine Oil Temperature Sensor A Range/Performance Moderate
- P209F Reductant Tank Heater Control Circuit Performance Moderate
- P2188 System Too Rich at Idle Bank 1 Moderate
- P2190 System Too Rich at Idle Bank 2 Moderate
- P24A2 Particulate Filter Regeneration Incomplete Bank 1 Moderate
- P2A50 Alternative Fuel Vaporizer A Outlet Temperature Sensor Circuit High
- P2A51 Alternative Fuel Vaporizer A Outlet Temperature Sensor Range/Performance High
- P2A52 Alternative Fuel Vaporizer A Outlet Temperature Sensor Circuit Low High
- P2A53 Alternative Fuel Vaporizer A Outlet Temperature Sensor Circuit High High
- P2A55 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit High
- P2A56 Alternative Fuel Vaporizer B Outlet Temperature Sensor Range/Performance High
- P2A57 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit Low High
- P2A58 Alternative Fuel Vaporizer B Outlet Temperature Sensor Circuit High High
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