P1115

DTC P1115 Engine Coolant Temperature Intermittent High Voltage

Circuit Diagram:

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 to 2.0 volts. If the ECM detects an ECT signal that is intermittently above the range of the ECT sensor, Diagnostic Trouble Code (DTC) P1115 will set.

Conditions for Setting the DTC
- ECT is less than -38 °C (-36 °F).
- Engine has been running for over 120 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.
- DTC(s) can be cleared by using the scan tool.
- Disconnecting the ECM battery feed for more than 10 seconds.

Diagnostic Aids
Check for the following conditions:
- Poor connection at the ECM. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection.
- 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 Fail 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 vs Resistance. [1][2]Computers and Control Systems

Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The On-Board Diagnostic (OBD II) System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data on the scan tool if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is then stored on the scan tool for later reference.

Step 1 - 7:

Step 8 - 10: