DTC P0128: Coolant Thermostat (Coolant Temperature Below Thermostat Regulating Temperature) [08/2013 - ]: Procedure

WARNING: This page is about a different car, the 2014 Lexus ES 300h. However, it is still accessible from the selected car via links, so may be relevant.

CHECK ANY OTHER DTCS OUTPUT (IN ADDITION TO DTC P0128)

Connect the Techstream to the DLC3.
Turn the power switch on (IG).
Turn the Techstream on.
Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

Read the DTCs.

RESULT

Result	Proceed to
DTC P0128 is output	A
DTC P0128 and other DTCs are output	B

HINT:

If any DTCs other than P0128 are output, troubleshoot those DTCs first.

B → See step 4

A: Go to next step

CHECK COOLING SYSTEM
1. Check for defects in the cooling system that might cause the system to be too cold, such as abnormal cooling fan operation or any modifications.
NG → REPAIR OR REPLACE COOLING SYSTEM

OK: Go to next step
INSPECT THERMOSTAT
1. Inspect the thermostat opening temperature. Refer to INSPECTION [08/2013 - ] .
NG → See step 5

OK → See step 6
GO TO DTC CHART. Refer to DIAGNOSTIC TROUBLE CODE CHART [08/2013 - ]
REPLACE THERMOSTAT. Refer to REMOVAL [08/2013 - ]
REPLACE ECM. Refer to REMOVAL [08/2013 - ]