<- Back Forward -> Document ID# 546741 2000 Chevrolet Chevy K Silverado - 4WD Print DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage Circuit Description The engine coolant temperature (ECT) sensor contains a semiconductor device which changes the resistance based on the temperature. The ECT sensor is mounted in the left bank cylinder head near the front of the engine. The ECT sensor has a signal circuit and a ground circuit. The powertrain control module (PCM) applies a voltage (about 5.0 volts) on the signal circuit to the sensor. The PCM monitors the changes in this voltage caused by changes in the resistance of the sensor in order to determine the coolant temperature. When the coolant is cold, the sensor resistance is high. The PCM signal voltage is only pulled down a small amount through the sensor to a ground, therefore, the PCM senses a high signal voltage. When the coolant is warm, the sensor resistance is low. The signal voltage is pulled down a greater amount, therefore, the PCM senses a low signal voltage (high temperature). At normal operating temperature, the voltage should measure about 1.5-2.0 volts at the PCM. When the PCM senses a signal voltage higher than the normal operating range of the sensor, this diagnostic trouble code (DTC) sets. The PCM sends the instrument panel cluster (IPC) ECT information via the Class 2 circuit. This information is used for controlling the coolant temperature gauge and for displaying a message when the coolant temperature is out of the normal operating range. The IPC displays a message when the ECT is more than 121 C (250 F). Conditions for Running the DTC The engine run time is more than 60 seconds.
OR The engine run time is less than 60 seconds when intake air temperature (IAT) is more than 0 C (32 F). Conditions for Setting the DTC The ECT is less than -39 C (-38 F). All conditions are met for 20 seconds. Action Taken When the DTC Sets The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records. The engine coolant temperature gauge defaults to a predetermined value. The message center will display a message. This may only be displayed briefly. Conditions for Clearing the MIL/DTC The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. A last test failed, or current DTC, clears when the diagnostic runs and does not fail. A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. Use a scan tool in order to clear the MIL and the DTC. Diagnostic Aids Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM. The following may cause an intermittent: - Poor connections - Mis-routed harness - Rubbed through wire insulation - Broken wire inside the insulation If the engine has sat overnight, the engine coolant temperature (ECT) and intake air temperature (IAT) values should display within a few degrees of each other. If the temperatures are not within 3 C (5 F), refer to Temperature vs Resistance. If you determine that the DTC occurs intermittently, performing the P1115 diagnostic table may isolate the cause of the fault. For an intermittent, refer to Symptoms.
http://127.0.0.1:9001/servlets/blobshtml?shtmlfile=546741&evc=sm&pubid=147&c... 16.03.2009 Test Description The numbers below refer to the step numbers on the diagnostic table. 2. This step determines if the malfunction is present. 4. Using the Freeze Frame and Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and Failure Records data can help determine how many miles since the DTC set. The Fail Counter and Pass Counter can also help determine how many ignition cycles the diagnostic reported a pass or a fail. Operate the vehicle within the same Freeze Frame conditions such as RPM, load, vehicle speed, temperature, etc. that you observed. This will isolate when the DTC failed. 5. An engine coolant temperature above 139 C (282 F) indicates the PCM and ECT sensor wiring is OK. 6. An engine coolant temperature above 139 C (282 F) indicates the PCM and ECT sensor signal circuit is OK. 7. Disconnecting the PCM allows using the DMM in order to check continuity of the circuits. This aids in locating an open or a shorted circuit. 8. Disconnecting the PCM allows using the DMM in order to check for a short to voltage. Step 1 2 3 4 Action Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? 1. Install a scan tool. 2. Turn ON the ignition, with the engine OFF. 3. Monitor the ECT sensor display on the Engine 1 Data List of the scan tool. Is the ECT sensor at the specified value? Are DTCs P1635 and P1639 also set? 1. Turn ON the ignition, with the engine OFF. 2. Review the Freeze Frame and Failure Records data for this DTC and observe the parameters. 3. Turn OFF the ignition for 15 seconds. 4. Start the engine. 5. Operate the vehicle within the conditions required for this diagnostic to run, and as close to the conditions recorded in the Freeze Frame and Failure Records as possible. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running Value (s) Yes No -39 C (-38 F) 2 Go to Powertrain On Board Diagnostic (OBD) System Check 3 4 14 5
the DTC. 6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool. 5 6 7 8 9 Does the scan tool indicate that this diagnostic failed this ignition? 1. Disconnect the ECT sensor electrical connector. 2. Jumper the ECT sensor harness terminals together. 3. Observe the ECT parameter on the scan tool. Is the ECT sensor at the specified value? Jumper the ECT sensor signal circuit to a known good ground. Is the ECT sensor at the specified value? 1. Turn OFF the ignition. 2. Disconnect the PCM connector C1 located on the same side of the manufacturers logo. Refer to Powertrain Control Module (PCM) Replacement. 3. Check the ECT sensor signal circuit for an open. Is the ECT sensor signal circuit open? 1. Turn OFF the ignition. 2. Remove the jumper harness from the ECT sensor harness connector. 3. Disconnect the PCM. Refer to Powertrain Control Module (PCM) Replacement. 4. Turn ON the ignition, with the engine OFF. 5. Probe the ECT signal circuit at the PCM harness connector using the DMM connected to ground. Refer to Probing Electrical Connectors in Wiring Systems. Does the DMM display a voltage? Check continuity from the ECT signal circuit to all other PCM circuits at the PCM harness connectors using the DMM. Refer to Testing for Continuity in Wiring Systems. Does the DMM display continuity within the specified range from the ECT sensor signal circuit to any other PCM circuit? 1. Turn OFF the ignition. 2. Disconnect the PCM connector C1 located on the same side of the manufacturers logo. Refer to Powertrain Control Module (PCM) Replacement. 140 C (284 F) 5 Go to Diagnostic Aids 8 6 140 C (284 F) 10 7 0-2 ohms 11 16 14 9 15 12
10 3. Inspect the ECT sensor ground circuit for an open. Refer to Testing for Continuity in Wiring Systems. Is the ECT sensor ground circuit open? 13 16 11 Repair the ECT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. 18 12 Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement. 18 13 Repair the ECT sensor ground circuit. Refer to Wiring Repairs in Wiring Systems. 18 14 Repair the ECT sensor signal circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems. 18 15 Repair the short between the ECT sensor signal circuit and the PCM circuit that had continuity. Refer to Wiring Repairs in Wiring Systems. 18 16 1. Inspect the PCM harness connector for poor connections. Refer to Testing for Intermittent and Poor Connections in Wiring Systems. 2. If you find a poor connection, repair the conditions as necessary. Refer to Connector Repairs in Wiring Systems. Did you find and repair the condition? 18 17 Important: The replacement PCM must be programmed. 17 Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement. 18 18 1. Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool. 2. Idle the engine at the normal operating temperature. 3. Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool. 4. Operate the vehicle within the Conditions for
19 Running the DTC as specified in the supporting text, if applicable. Does the scan tool indicate that this test ran and passed? Select the Capture Info option and the Review Info option using the scan tool. Does the scan tool display any DTCs that you have not diagnosed? 19 2 Go to the applicable DTC table System OK <- Back Forward -> Document ID# 546741 2000 Chevrolet Chevy K Silverado - 4WD Print