For 1990-2009 cars
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Handling ESD Sensitive Parts Notice

### Circuit Description

The Engine Coolant Temperature (ECT) sensor contains a semiconductor device which changes the resistance based on the temperature (a thermistor). 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 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 (thermistor) resistance is high. The PCMs signal voltage is only pulled down a small amount through the sensor to a ground; therefore, the PCM senses a high signal voltage (low temperature). 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 DTC sets.

The engine coolant temperature information is sent to the instrument panel cluster via the class 2 circuit.

### Conditions for Running the DTC

• | The engine run time is greater than 60 seconds.

| OR

• | The engine run time is less than 60 seconds when the IAT is greater than 0°C (32°F).

### Conditions for Setting the DTC

• | The Engine Coolant Temperature is less than -39°C (-38°F).

• | All conditions 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.

### 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/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminant intrusion into the PCM.

• | For any test that requires probing the PCM or component harness connectors, use the Connector Test Adapter Kit J 35616 . Using this kit prevents any damage to the harness connector terminals. Refer to Using Connector Test Adapters in Wiring Systems.

• | 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 and intake air temperature 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.

• | Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or 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 and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed.

• | For an intermittent, refer to Symptoms .

### Test Description

The numbers below refer to the step numbers on the diagnostic table.

1. This step determines if the malfunction is present.

2. If DTC P1635 and P1639 set at the same time, this indicates that the signal circuit is shorted to a voltage.

3. Using the Freeze Frame and/or Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or 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 and/or a fail. Operate the vehicle within the same freeze frame conditions (RPM, load, vehicle speed, temperature etc.) that you observed. This isolates when the DTC failed.

4. An engine coolant temperature above 139°C (282°F) indicates the PCM and ECT sensor wiring is OK.

5. An engine coolant temperature above 139°C (282°F) indicates the PCM and ECT sensor signal circuit is OK.

6. Disconnecting the PCM allows using the DMM in order to test continuity of the circuits. This aids in locating an open or a shorted circuit.

7. Disconnecting the PCM allows using the DMM in order to test for a short to voltage.

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

1. Install a scan tool.
2. Turn ON the ignition leaving 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?

-39°C (-38°F)

Go to Step 3

Go to Step 4

3 | Are DTCs P1635 and P1639 also set? | -- | Go to Step 14 | Go to Step 5
4 |

1. Turn ON the ignition leaving the engine OFF.
2. Review the Freeze Frame and/or 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/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 the DTC.
6. Select the Diagnostic Trouble Code (DTC) option, the Specific DTC option, then enter the DTC number using the scan tool.

Does the scan tool indicate that this diagnostic failed this ignition?

--

Go to Step 5

Go to Diagnostic Aids

5 |

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?

140°C (284°F)

Go to Step 8

Go to Step 6

6 | Jumper the ECT sensor signal circuit to a known good ground. Is the ECT sensor at the specified value? | 140°C (284°F) | Go to Step 10 | Go to Step 7
7 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector C1 located on the same side as the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
3. Test the ECT sensor signal circuit for an open.

Is the ECT sensor signal circuit open?

--

Go to Step 11

Go to Step 16

8 |

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 Replacement/Programming .
4. Turn ON the ignition leaving the engine OFF.
5. Probe the ECT signal circuit at the PCM harness connector using the DMM J 39200 connected to ground. Refer to Probing Electrical Connectors in Wiring Systems .

Does the DMM display a voltage?

--

Go to Step 14

Go to Step 9

9 | Test for continuity from the ECT signal circuit to all other PCM circuits at the PCM harness connectors using the DMM J 39200 . Example: probe one lead to the ECT sensor signal circuit (at the PCM harness connector) and probe the other lead to each terminal at the PCM harness connectors. 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?

0-2ohms

Go to Step 15

Go to Step 12

10 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector C1 located on the same side as the manufacturer's logo. Refer to Powertrain Control Module Replacement/Programming .
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?

--

Go to Step 13

Go to Step 16

11 | Repair the ECT sensor signal circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 18 | --
12 | Replace the ECT sensor. Refer to Engine Coolant Temperature Sensor Replacement . Is the action complete? | -- | Go to Step 18 | --
13 | Repair the ECT sensor ground circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 18 | --
14 | Repair the ECT sensor signal circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems . Is the action complete? | -- | Go to Step 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. Is the action complete? | -- | Go to Step 18 | --
16 |

1. Inspect the PCM harness connector for poor connections. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems .
2. If you find a poor connection, repair the conditions as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you find and repair the condition?

--

Go to Step 18

Go to Step 17

17 | Important: Program the replacement PCM. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Is the action complete? | -- | Go to Step 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 Running the DTC as specified in the supporting text, if applicable.

Does the scan tool indicate that this test ran and passed?

--

Go to Step 19

Go to Step 2

19 | 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? | -- | Go to the applicable DTC table | System OK