P0128 Coolant thermostat below regulating temperature
- System
- Powertrain - engine and transmission
What P0128 means
"Coolant thermostat below regulating temperature" is a comparison against time as much as temperature. The computer works out how warm the coolant should have become by now, from how long the engine has run and how cold the air is, and files this code when the reported coolant temperature stayed below that figure. It is a statement about a reading not rising as modelled, nothing more.
This is a standard code. It means the same thing on every make of vehicle.
What the program shows for P0128
Coolant temp is the reading in question and it sits on the Dashboard with its own normal band, beside Intake air temp and Outside air, which are the other figures the comparison uses. Recording a drive from a cold start keeps all three, and Replay plays them back, so the warm-up can be watched again rather than remembered.
The Dashboard shows Short fuel trim and Long fuel trim, Air flow, Manifold pressure, Intake air temp, Coolant temp, Throttle position, Accelerator pedal, Air/fuel ratio, O2 sensor (rear), O2 sensor current and whether the Fuel system is in closed loop. Record a drive and the Analysis screen gives the total correction At idle, Fuel trim against air flow, and whether the air flow and pressure sensors agree; the Full scan's On-board self-tests list the Oxygen sensor results by bank and sensor. Record before and after a repair and Compare shows the change in short, long and total trim at idle plus which codes are Gone, New or Still there.
See how the program shows a code →