P0118
Engine Coolant Temperature (ECT) Sensor Circuit High Voltage:
Engine Coolant Temperature (ECT) Sensor Circuit High Voltage (continued):
Engine Coolant Temperature (ECT) Sensor:
Engine Coolant Temperature (ECT) Sensor Circuit:
Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor (a variable resistor that changes along with engine coolant temperature) in series with a fixed resistor in the Powertrain Control Module (PCM). The PCM applies 5 volts to the ECT sensor. The PCM monitors the voltage across the ECT sensor and converts it into a temperature reading. When the engine is cold the ECT sensor resistance is high, and when the engine is warm the ECT sensor resistance is low. Therefore, when the engine is cold the PCM will receive a high voltage input, and when the engine is warm the PCM will receive a low voltage input.
Conditions for Setting the DTC
^ ECT sensor signal indicates an engine coolant temperature less than -40°C (-40°F).
^ Above condition is met for at least 0.5 seconds.
Action Taken When the DTC Sets
^ The Malfunction Indicator Lamp (MIL) will illuminate.
^ The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer.
Conditions for Clearing the MIL/DTC
^ The MIL will turn "OFF" after three consecutively passing cycles without a fault present.
^ A History DTC will clear after 40 consecutive warm-up cycles without a fault.
^ DTC(s) can be cleared by using a scan tool or by disconnecting the PCM battery feed.
Diagnostic Aids
Check The Following Conditions:
^ Poor connection at PCM. 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 to the fault.
^ When replacing the ECT sensor the "Temperature to Resistance Value" scale may be used to test the sensor at various temperature levels to evaluate the possibility of a "shifted" (mis scaled) sensor. A "shifted" sensor could result in poor driveability complaints. Specifications
^ After the engine is started, the ECT sensor should rise steadily to about 95°C (203°F) and stabilize when thermostat opens.
Verify that the engine is not overheating and has not been subjected to conditions which could create an overheating conditions (i.e., overload, trailer towing, hilly terrain, heavy stop and go traffic, etc.).
^ DTC P0108, P0113, P0118, P0123 are set together it is possible to have an open ground circuit (LT. GRN/BLK wire).
^ A shorted to voltage sensor signal circuit may cause DTC P0118 to set.
The cooling fan will turn ON when the DTC sets.
If DTC P0118 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
If any wiring repairs need to be made, Refer to Repair Procedures in Diagrams.
Test Description
Number(s) below refer to the step number(s) on the Diagnostic Table.
1. The Powertrain OBD system check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
2. Determines if fault is present.
3. Review Freeze Frame data to determine when the DTC set. Always record this information.
4. This step determines if the fault is caused by an open or shorted signal return circuit, a open in the ground circuit or by a malfunctioning ECT sensor.