Circuit Description
The Engine Coolant Temperature (ECT) sensor is a thermistor which controls the signal voltage to the PCM. The PCM applies a voltage on the 5 volt reference circuit to the sensor. The sensor resistance is high when the engine is cold. Therefore, the PCM senses a high voltage signal and the PCM indicates a low coolant temperature. The sensor resistance becomes less as the engine warms and the voltage drops indicating high coolant temperature. The voltage measures about 1.5 to 2.0 volts at normal engine operating temperature 85°C to 95°C (185°F to 203°F).
This is a type B DTC.
Conditions for Setting the DTC
The following conditions will set the DTC:
| • | The vehicle is in the CNG operation mode. |
| • | The engine has been running longer than 5 seconds. |
| • | The ECT circuit voltage is less than 0.019 volt. |
Action Taken When the DTC Sets
The ECU sets the DTC 15 after 2 consecutive driving trips with the fault active.
Conditions for Clearing the MIL/DTC
The ECU turns the MIL OFF after 3 consecutive driving trips without a fault condition present. A DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 40°C (72°F) from the start-up coolant temperature and the engine coolant temperature exceeds 70°C (160°F) during that same ignition cycle) or the code clearing procedure has been used.
Diagnostic Aids
Always diagnose ANY PCM codes that are present before beginning this diagnostic procedure.
The temperature should rise steadily to about 90°C (194°F) after starting the engine. The temperature will stabilize when the thermostat opens. A faulty connection or an open in the 5 volt reference circuit or the sensor ground circuit results in a DTC 15.
Use the Temperature vs. Resistance Value Table to test the coolant sensor at various temperature levels in order to evaluate the possibility of a skewed (mis-scaled) sensor. A skewed sensor could result in poor driveability complaints. Refer to Temperature vs. Resistance in Engine Controls - 2.2L in the J Platform Service Manual.
Test Description
The number(s) below refer to the step number(s) on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
1 | Was the Alternative Fuels (AF) Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | Go to Step 2 | Go to AF Powertrain OBD System Check |
2 |
Is the temperature greater than the specified value? | 138°C (280°F) | Go to Step 3 | Go to Step 4 |
Is the reading on the DVOM below the specified value? | 0.019 V | Go to Step 5 | Go to Step 9 | |
4 |
Is there continuity? | -- | Go to Step 8 | Go to Step 10 |
5 |
Is the temperature less than the specified value? | 138°C (280°F) | Go to Step 8 | Go to Step 6 |
6 |
Is the temperature less than the specified value? | 138°C (280°F) | Go to Step 10 | Go to Step 7 |
7 | Measure for continuity between the ECU side of C018 and ground using a DVOM. Is there continuity? | -- | Go to Step 10 | Go to DTC P0117 ECT Sensor Circuit Low in Engine Controls 2.2L in the 1998 J Platform Service Manual |
8 | Inspect the ECU connector and pins. Were any problems found? | -- | Go to Step 10 | Go to Step 11 |
9 | The DTC is intermittent. Refer to Diagnostic Aids if no additional DTCs were stored. If any additional DTCs are stored, refer to those tables. Are any additional DTCs set? | -- | Go to the applicable DTC table | Go to Diagnostic Aids |
10 | Repair the faulty or shorted circuit or connection. Refer to Wiring Repairs in Engine Controls - 2.2L in the J Platform Service Manual. Is the action complete? | -- | Go to Step 12 | -- |
11 | Replace the ECU. Refer to Engine Control Unit Replacement . Is the action complete? | -- | Go to Step 12 | -- |
12 |
Does the diagnostic run and pass? | -- | Go to Step 13 | Go to Step 2 |
13 | Are any ECU or PCM DTCs displayed that have not been diagnosed? | -- | Go to the applicable DTC table | System OK |
