S2118000009

Case Number: S2118000009
Release Date: May 2021
Symptom/Vehicle Issue:
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.
Discussion:
Perform steps 1 and 2 of the published diagnostic routine for P0128 found in Service Library for the
applicable vehicle. If issues were not identified during step 2 (Check the Cooling System Operation)
of the P0128 diagnostic, then perform the following check for the engine coolant temperature sensor
before replacing the thermostat:
Remove the coolant temperature sensor and check the electrical resistance between the metal shell
and connector pin 1 using an ohmmeter.
The electrical resistance between the shell and connector pin 1 should be greater than 1MΩ. If the
resistance is lower than 1MΩ, then replace the engine coolant temperature sensor and verify this
resolves the customer’s issue. If the issue is not resolved, or if the resistance reading is above 1MΩ,
then continue with the normal diagnostic repair procedure for P0128 fault code.
This document does not authorize warranty repairs. This communication documents a record of past experiences. STAR Online
does not provide any conclusions about what is wrong with the vehicle. Rather, it captures all previous cases known that appear
to be similar or related to the vehicle symptom / condition. You are the expert, and you are responsible for deciding on the
appropriate course of action.
Contact STAR Center, or your Technical Assistance Center Via TechCONNECT or eCONTACT ticket if no
solution is found
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