Circuit Description
The engine coolant temperature sensor (ECT) is a thermistor mounted in the engine coolant stream. The engine control module (ECM) applies 5-volt reference voltage through a pull-up resistor to the ECT signal circuit. When the engine coolant is cold, the sensor resistance is high, and the ECM will monitor a high signal voltage. As the engine coolant warms, the sensor resistance is less, and the ECT signal voltage measured at the ECM drops. With a fully warmed engine, the ECT signal voltage should measure about 1.5-2 volts. If the ECM detects an ECT signal that is intermittently above the range of the ECT sensor, DTC P1115 will set.
Conditions for Setting the DTC
| • | The ECT is less than -38°C (-36°F). |
| • | The engine has been running for over 90 seconds. |
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) will not illuminate. |
| • | The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data. |
| • | A history DTC is stored. |
Conditions for Clearing the MIL/DTC
| • | A history DTC will clear after 40 consecutive warm-up cycles without a fault. |
| • | DTCs can be cleared by using the scan tool. |
| • | Disconnect the ECM battery feed for more than 10 seconds. |
Diagnostic Aids
Inspect for the following conditions:
| • | A poor connection at the ECM--Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and a poor terminal-to-wire connection. |
| • | A damaged harness--Inspect the wiring harness for damage. If the harness appears to be OK, observe the ECT display on the scan tool while moving connectors and wiring harnesses related to the ECT sensor. A change in the ECT display will indicate the location of the fault. |
| • | Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition. |
| • | Use the Temperature vs. Resistance Values table to evaluate the possibility of a skewed sensor. Refer to Temperature Versus Resistance . |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
Step | Action | Yes | No |
|---|---|---|---|
Perform an On-Board Diagnostic System Check. Was the check performed? | Go to Step 2 | ||
2 |
Is DTC P0118 set? | Go to applicable DTC table | Go to Step 3 |
3 | Is DTC P1111 also set? | Go to Step 7 | Go to Step 4 |
4 | Inspect for a poor sensor ground circuit terminal 2 at the engine coolant temperature (ECT) sensor and repair as needed. Did you find and correct the condition? | Go to Step 9 | Go to Step 5 |
5 | Inspect for a poor sensor signal circuit between terminal 1 of the ECT sensor and terminal A11 of the engine control module (ECM) for an intermittent open and repair as needed. Did you find and correct the condition? | Go to Step 9 | Go to Step 6 |
6 | Inspect for sensor signal circuit between terminal 1 of the ECT sensor and terminal A11 of the ECM for an intermittent short to voltage and repair as needed. Did you find and correct the condition? | Go to Step 9 | Go to Step 7 |
7 | Inspect for poor sensor ground circuit terminal A32 at the ECM and repair as needed. Did you find and correct the condition? | Go to Step 9 | Go to Step 8 |
8 | Inspect for an intermittent open or a faulty splice in the sensor ground circuit and repair as needed. Did you find and correct the condition? | Go to Step 9 | Go to Diagnostic Aids |
9 |
Does the scan tool indicate that this diagnostic has run and passed? | Go to Step 10 | Go to Step 2 |
10 | Are any DTCs displayed that have not been diagnosed? | Go to applicable DTC table | System OK |
