DTC P1115 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage. Pontiac Grand Prix 1999

For 1990-2009 cars only

Makes 🢒 Pontiac 🢒 1999 🢒 Grand Prix 🢒 DTC 🢒 DTC P1115 Engine Coolant Temperature (ECT) Sensor Circuit Intermittent High Voltage

Cell 20: Power, Ground, MIL, and DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

The Engine Coolant Temperature (ECT) sensor is a thermistor mounted in the engine coolant stream. The PCM applies a voltage (about 5.0 volts) through a pull up resistor to the ECT signal circuit. When the engine coolant is cold, the sensor (thermistor) resistance is high; therefore the PCM will measure a high signal voltage. As the engine coolant warms, the sensor resistance becomes less, and the ECT signal voltage measured at the PCM drops. With a fully warmed up engine, the ECT signal voltage should measure about 1.5 to 2.0 volts. If the PCM detects an ECT signal that is intermittently above the range of the ECT sensor, DTC P1115 will set.

Conditions for Running the DTC

Engine running.

Conditions for Setting the DTC

•	The ECT sensor is intermittently less than -39°C (-38°F)

•	Above conditions present for longer than 3 seconds.

Action Taken When the DTC Sets

The PCM stores conditions which were present when the DTC set as Failure Records only. This information will not be stored as Freeze Frame Records.

Conditions for Clearing the MIL/DTC

•	The DTC becomes history when the conditions for setting the DTC are no longer present.

•	The history DTC clears after 40 malfunction free warm-up cycles.

•	The PCM receives a clear code command from the scan tool.

Diagnostic Aids

Check for the following conditions:

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

•	Poor terminal connection.

Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Use a corresponding mating terminal to test for proper tension. Refer to Intermittents and Poor Connections Diagnosis , and Connector Repairs Wiring Systems.

•	Damaged harness.

Inspect the wiring harness for damage. If the harness appears to be OK, observe the sensor display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the sensor display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems.

•	Inspect the PCM and the engine grounds for clean and secure connections.

If the DTC is determined to be intermittent, reviewing the Fail Records can be useful in determining when the DTC was last set.

Step	Action	Value(s)	Yes	No
1	Was the Powertrain on Board Diagnostic System Check performed?	--	Go to Step 2	Go to Powertrain On Board Diagnostic (OBD) System Check
2	Select DTC info, Last Test Fail and note any other DTCs set. Is DTC P0118 also set?	--	Go to DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage	Go to Step 3
3	Is DTC P1106, P1111, and/or P1121 also set?	--	Go to Step 8	Go to Step 4
4	Check for a poor sensor ground circuit terminal connection at the ECT sensor. If a problem is found, repair as necessary. ssary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Was a problem found?	--	Go to Step 10	Go to Step 5
5	Check for a poor ECT signal circuit terminal connection at the ECT sensor. If a problem is found, repair as necessary. ssary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Was a problem found?	--	Go to Step 10	Go to Step 6
6	Check the ECT signal circuit between the ECT sensor connector and the PCM for an intermittent open. If a problem is found, repair as necessary. ssary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Was a problem found?	--	Go to Step 10	Go to Step 7
7	Check the ECT signal circuit between the ECT sensor connector and the PCM for an intermittent short to voltage. If a problem is found, repair as necessary. ssary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Was a problem found?	--	Go to Step 10	Go to Step 8
8	Check for a poor sensor ground circuit terminal connection at the PCM. If a problem is found, repair as necessary. ssary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Was a problem found?	--	Go to Step 10	Go to Step 9
9	Check for an intermittent open or a faulty splice in the sensor ground circuit. If a problem is found, repair as necessary. ssary. Refer to Testing for Continuity Intermittents and Poor Connections Diagnosis Repairing Connector Terminals and Connector Repairs . Was a problem found?	--	Go to Step 10	Go to Diagnostic Aids
10	Review and record scan tool Fail Records data. Clear DTCs. Operate vehicle within Fail Records conditions as noted. Using a scan tool, monitor Specific DTC info for DTC P1115. Does scan tool indicate DTC P1115 failed?	--	Go to Step 2	System OK