1. Install EST and check for active and inactive DTCs related to engine coolant over-temp conditions.
• If any DTCs remain relating to coolant over-temp condition, correct DTC before continuing.
• If no DTCs exist, do step 2.
2. Using the EST, compare Engine Coolant Temperature (ECT), Engine Oil Temperature (EOT), and Manifold Air Temperature (MAT) with Key On Engine Off. All of the sensors should read within 2° C (5° F) of each other.
NOTE: This is only accurate if done after a cold soak of at least 8 hours on the engine.
3. Install a manual gauge or DMM with a thermocouple in the EGR cooler inlet port, operate the engine, and use the EST to monitor ECT.
4. Run engine up to an operating temperature of atleast 70° C (158° F). While monitoring ECT using the EST, instrument panel coolant temperature gauge and the mechanical or electrical gauge.
Attempt to duplicate the operator’s concern of coolant over-temp.
• If instrument panel coolant temperature gauge reads a different temperature than the EST and test gauge, refer to the Electrical System Troubleshooting Guide for the appropriate model and year of vehicle.
• If test gauge and EST read values with a difference greater than +/- 3° C (+/- 5° F), do Electronic Control Systems Diagnostics for ECT circuit found in Section 7 of this manual.
• If the gauge is reading correctly and the engine is running over-temperature, go to “Cooling System Operating Pressure Test” (page 121) in this section.