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 below the range of the ECT sensor, diagnostic trouble code (DTC) P1114 will set.
DTC Descriptor
This diagnostic supports the following DTC:
DTC P1112 Intake Air Temperature (IAT) Sensor Circuit Intermittent Low Voltage
Conditions for Setting the DTC
| • | The ECM detects that the intake air temperature (IAT) is more than 209°C (909°F) intermittently. |
| • | The condition exists for more than 20 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
Check 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 . |
| • | For an intermittent condition, refer to Intermittent Conditions . |
Step | Action | Yes | No |
|---|---|---|---|
Schematic Reference: Engine Controls Schematics Connector End View Reference: Engine Controls Connector End Views | |||
1 | Did you perform the Diagnostic System Check - Engine Controls? | Go to Step 2 | |
2 | Observe the DTC Information with a scan tool. Is DTC P0112 set? | Go to DTC P0117 | Go to Step 3 |
3 | Observe the intake air temperature (IAT) sensor parameter with a scan tool while moving the IAT sensor connector and the engine control module (ECM) connector. Refer to Inducing Intermittent Fault Conditions in Wiring Systems. Does the scan tool indicate an abrupt change in value? | Go to Step 5 | Go to Step 4 |
4 | Observe the IAT sensor parameter with a scan tool while moving the wiring harness between the IAT sensor and the ECM. Refer to Inducing Intermittent Fault Conditions in Wiring Systems. Does the scan tool indicate an abrupt change in value? | Go to Step 6 | Go to Diagnostic Aids |
5 | Repair the connector/terminal as necessary. Refer to Connector Repairs in Wiring Systems. Did you complete the repair? | Go to Step 7 | -- |
6 | Repair the harness/wiring as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 7 | -- |
7 |
Did the DTC fail this ignition? | Go to Step 2 | Go to Step 8 |
8 | Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? | System OK | |
