Heavy Duty Thermostat Monitor (2016)
For the 2016 MY, the Heavy Duty OBD regulations require an enhancement to the thermostat test. As in the past, the thermostat monitor requires monitoring of the following:
- The coolant temperature does not reach the highest temperature required by the OBD-II system to enable other diagnostics;
- The coolant temperature does not reach a warmed-up temperature within 20 deg F of the manufacturer's nominal thermostat regulating temperature
For 2016 MY, the monitor becomes continuous and adds the following:
- The coolant temperature has reached regulating temperature and then drops below the thermostat malfunction threshold
The enhanced diagnostic will continue to set the P0128 DTC. The test consists of two portions:
Cold start engine warm-up test (existing monitor)
The ECT model is used to determine when the engine is expected to be fully warmed up to the thermostat regulating temperature. At that time, the measured ECT is expected to be above the thermostat malfunction threshold (within 20 deg F of thermostat regulating temperature).
Warm engine continuous test (new HD OBD Requirement)
The continuous portion is enabled once the cold start engine warm-up test has completed and determined that no fault exists and the measured ECT has exceeded thermostat regulating temperature. Once enabled, if measured ECT drops below the thermostat fault threshold, the ECT model is reinitialized so that the cold start monitor can run again. Once the ECT model gets to thermostat regulating temperature, the measured ECT is expected to be above the thermostat malfunction threshold.
A P0128 DTC is set if measured ECT < Tstat Threshold once modeled ECT has exceeded Tstat Regulating Temperature for 3 secocnds.
