GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Cadillac 🢒 1996 🢒 DeVille 🢒 DTC 🢒 DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage

Object Number: 12983 Size: SF
Engine Controls Components
IAT/ ECT/ TP/ MAP and BBV Sensors
OBD II Symbol Description Notice
ESD Notice
ESD Notice

Circuit Description

The Engine Coolant Temperature sensor is a thermistor, a sensor whose resistance varies with temperature. The ECT sensor signal is on CKT 410 and sensor ground on CKT 808. As the temperature increases, sensor resistance decreases. Low coolant temperature will result in high signal voltage on CKT 410. DTC P0118 sets because the coolant temperature cannot be less than -38°C (-36°F) when IAT is greater than -5°C (23°F) or the engine has been running long enough too warm above -38°C (-36°F).

Conditions for Setting the DTC

Test Conditions

    • DTCs P0112 and P0113 not set.
    • IAT sensor value -5°C (23°F) or greater.

OR

    • DTCs P0122 and P0123 not set.
    • Engine running with throttle angle 7 degrees or greater for at least 3.5 minutes.

Failure Condition

The ECT sensor reading is -38°C (-36°F) or lower when one of the above sets of test conditions have been met.

Action Taken When the DTC Sets

    •  The PCM will illuminate the malfunction indicator lamp (MIL) when the diagnostic runs and fails.
    •  The PCM will record operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame and Failure Records.

Conditions for Clearing the MIL/DTC

    •  The PCM will turn the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
    •  A Last Test Failed (current) DTC will clear when the diagnostic runs and does not fail.
    •  A History DTC will clear after forty consecutive warm-up cycles with no failures of any emission related diagnostic test.
    • Use a scan tool to clear DTCs.
    • Interrupting PCM battery voltage may or may not clear DTCs. This practice is not recommended. Refer to Clearing Diagnostic Trouble Codes in PCM Description and Operation.

Diagnostic Aids

If fault is not present perform Powertrain Ground Check and also review Failure Rec. to determine conditions under which and how long ago the DTC set.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. Checking for an open in the ECT sensor signal Circuit from PCM to sensor. If the display shows 135°C (275°F) to 151°C (304°F) with the coolant temperature sensor wiring harness terminals jumpered together, then the ECT sensor signal circuit and the ECT sensor ground circuit are OK.

    2.

  2. Checking for an open in the ECT sensor ground circuit. If shorting the ECT sensor signal circuit to ground causes ECT display to show 135°C (275°F) to 151°C (304°F), then there is an open in the ECT sensor ground circuit.

Step

Action

Value(s)

Yes

No

1

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to A Powertrain On Board Diagnostic (OBD) System Check

2
  1. Connect a scan tool
  2. Turn the key ON.
  3. View the ECT sensor display.

Is the temperature the same or less than the value specified?

-35°C (-31°F)

Go to Step 3

Fault not present. Refer to Diagnostic Aids

3

  1. Disconnect ECT sensor connector.
  2. Jumper harness terminals A and B together.

Is the temperature more than the value specified?

135°C (275°F)

Go to Step 9

Go to Step 4

4

Connect a jumper from ECT sensor signal terminal (harness side) to ground.

Is the temperature more than the value specified?

135°C (275°F)

Go to Step 6

Go to Step 5

5
  1. Remove the jumper.
  2. Record the fluid life indexes, turn the key to OFF and wait 30 seconds.
  3. Disconnect PCM connector C2.
  4. Using DMM J 39200 measure the resistance between PCM connector C2 terminal 74 and the ECT sensor signal terminal.

Is the resistance the same or less than the value specified?

5 ohms

Go to Step 11

Go to Step 7

6
  1. Remove the jumper.
  2. Record the fluid life indexes, turn the key to OFF and wait 30 seconds.
  3. Disconnect PCM connector C1.
  4. Using DMM J 39200 measure the resistance between PCM connector C1 terminal 17 and the ECT sensor ground terminal.

Is the resistance the same or less than the value specified?

5 ohms

Go to Step 11

Go to Step 8

7

Repair the open in the ECT sensor signal circuit.

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

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8

Repair the open in the ECT sensor ground circuit.

Is the repair complete?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

--

9
  1. Check terminal contact at the ECT sensor.
  2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 10

10

Replace the ECT sensor. Refer to Engine Coolant Temperature (ECT) Sensor Replacement .

Is the replacement complete?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

--

11
  1. Check terminal contact at the PCM connector C1 terminal 7 and connector C2 terminal 74.
  2. Repair terminal contact if needed.

Was terminal contact repaired?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

Go to Step 12

12

Replace the PCM. Refer to PCM Replacement/Programming .

Is the replacement complete?

--

Go to Powertrain Control Module Diagnosis for Verify Repair

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