P0128 on Jeep vehicles The engine is not reaching its normal operating temperature in the expected time — usually the thermostat

A model year is listed because the code is named in its own record — a bulletin filed against it, or an owner’s complaint about it — not because every one of these vehicles sets it. Counts are documents in NHTSA’s files, not failure rates.

Owners’ own words, scrubbed of anything identifying. Unverified reports filed with NHTSA — what was said, not a finding that it was true.

Bulletins and campaigns Jeep filed with NHTSA whose summary names P0128. Quote the document number at the service desk — it is a diagnosis the maker has already written down.

• 18-012-19 REV A Service bulletin
  2019-05-29 · Power Train
• Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find that one or more of the following DTCs have been set:P0456 - EVAP System Small Leak. P0128 - Thermostat Rationality. The following software enhanc
• 18-037-19 REV. A Service bulletin
  2019-08-14 · Power Train
• Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. The customer may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find one or more of the following DTCs: P050B - Cold Start Ignition Timing Performance. P0456 - EVAP System Small Leak. P0128 - Thermostat Rational
• 18-012-19 REV. C Service bulletin
  2019-08-14 · Power Train
• Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find that one or more of the following DTCs have been set:P050B - Cold Start Ignition Timing Performance. P0456 - EVAP System Small Leak. P0128 - Ther
• 18-041-19 Service bulletin
  2019-05-04 · Power Train — Automatic Transmission — Control Module (Tcm/Pcm/Tecm)
• Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the Powertrain Control Module (PCM) with thelatest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find that one or moreof the following DTCs have been set: P0456 - EVAP System Small Leak(APAC&EMEA with Sales Codes NA1 wit
• 18-014-20 Service bulletin
  2020-02-19 · Electrical System — Software
• Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find that one or more of the following DTCs have been set:P0456 - EVAP System Small Leak. If DTC P0456 is present use wiTECH Small Leak Verification T
• 18-014-20 REV. A Service bulletin
  2020-03-18 · Power Train
• Flash: Powertrain Control Module (PCM) Updates This bulletin involves reprogramming the PCM with the latest available software. Customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find that one or more of the following DTCs have been set:P0456 - EVAP System Small Leak. If DTC P0456 is present use wiTECH Small Leak Verification Te
• S2118000009 Service bulletin
  2021-05-24 · Engine And Engine Cooling
• Customer complains of a MIL-on condition. Upon further inspection, there is a Diagnostic Trouble Code (DTC) P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) set in the PCM.
• S2118000009 Service bulletin
  2021-05-24 · Engine And Engine Cooling
• Customer complains of a MIL-on condition. Upon further inspection, there is a Diagnostic Trouble Code (DTC) P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) set in the PCM.
• S2118000009 Service bulletin
  2021-05-24 · Engine And Engine Cooling
• Customer complains of a MIL-on condition. Upon further inspection, there is a Diagnostic Trouble Code (DTC) P0128 Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) set in the PCM.
• 18-061-16 REV. C Service bulletin
  2016-11-11 · Power Train — Automatic Transmission — Control Module (Tcm/Pcm/Tecm)
• Flash: Powertrain Diagnostic And System EnhancementsThis bulletin involves reprogramming the Powertrain Control Module (PCM) with the latest available software. A small number of customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation the technician may find one or more of the following DiagnosticTrouble Codes (DTCs):P0128 - Thermostat Rationality. P03
• 18-032-17 Service bulletin
  2017-03-31 · Power Train
• Flash: Powertrain Diagnostic And System Improvements This bulletin involves reprogramming the Powertrain Control Module (PCM) with the latest available software. A small number of customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation, the technician may find one or more of the following DTCs: P1186 - Cylinder 1 Oil Supply Solenoid Valve Switch O
• 18-032-17 Service bulletin
  2017-03-31 · Back Over Prevention
• Flash: Powertrain Diagnostic And System Improvements This bulletin involves reprogramming the Powertrain Control Module (PCM) with the latest available software. A small number of customers may experience a Malfunction Indicator Lamp (MIL) illumination. Upon further investigation, the technician may find one or more of the following DTCs: P1186 - Cylinder 1 Oil Supply Solenoid Valve Switch O

A stored code names the test that failed, never the part that caused it. The record above is what Jeep and its owners have filed about it; the code’s page across every make has the whole file.