P0117 Engine Coolant Temperature sensor circuit low

P0117 code - theory of Operation, at key on, the Powertain Control Module (PCM) sends out a regulated 5 volt signal to the ECT sensor. The PCM then monitors the signal as it passes through the ECT sensor to the sensor ground (sensor return). When the engine is cold, the PCM will operate in open loop cycle. It will demand slightly richer air-fuel mixtures and higher idle speeds. This is done until normal operating temperatures are reached. When monitored P0117 code with the ignition on, battery voltage greater than 10.4 volts. Set condition the ECT sensor input voltage is below the minimum acceptable value. Default actions the MIL Light illuminate, the ETC Light will illuminate, throttle input and vehicle speed are limited.

The PCM uses inputs form the ECT sensor for the following calculations:

• For engine coolant temperature gauge operation through CCD or PCI (J1850) communications.
• Injector pulse-widht.
• ASD relay shut down times.
• Sprak-advance curves.
• Idle Air Control (IAC) motor key-on steps.
• Pulse-widht prime-short during cranking.
• O2 sensor closed loop times.
• Purge solenoid on/off times.
• EGR solenoid on/off times (if equipped).
• Leak detection pump operation (if equipped).
• Radiator fan relay on/off times (if equipped).
• Target idle speed.

Possible causes P0117 code:

• ECT signal circuit shorted to ground.
• ECT signal circuit shorted to the sensor ground.
• Engine Coolant Temperature (ECT) sensor.
• Powertrain Control Module (PCM).

Diagnose code P0117 Engine Coolant Temperature sensor circuit low

Step 1. Active DTC

Start the engine and allow it to reach normal operating temperature. Diagnose and repair any system voltage DTC before continuing with this test. With the scan tool, select view DTC.

Is the DTC active at this time?

Yes, go to step 2.

No, perform the PCM intermittent condition.

Step 2. ECT sensor

Turn the ignition off, disconnect the ECT harness connector. Turn the ignition on, engine not running, with the scan tool, read ECT voltage.The sensor voltage should be approximately 5.0 volts (plus or minus 1 volt) with the connector disconnected.

Does the scan tool display the voltage as discribed above?

Yes, verify that there is good pin to terminal contact in the ECT sensor and Powertrain Control Module (PCM) connectors. If OK, replace the ECT sensor.

No, go to step 3.

Step 3. ECT signal circuit shorted to the sensor ground circuit

Turn the ignition off, disconnect the PCM harness connector. Measure the resistance between the sensor ground circuit and the ECT signal circuit in the ECT sensor harness connector.

Is the resistance below 5.0 Ohms?

Yes, repair the short to between the sensor ground circuit and the ECT signal circuit.

No, go to step 4.

Step 4. ECT signal circuit shorted ground

Measure the resistance between ground and the ECT signal circuit in the ECT sensor harness connector.

Is the resistance below 100 Ohms?

Yes, repair the short to ground in the ECT signal circuit.

No, go to step 5.

Step 5. Powertrain Control Module (PCM)

Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the ECT sensor and the Powertrain Control Module (PCM). Look for any chafed, pierced, pinched or partially broken wires. Look for broken, bent, pushed out or corroded terminals. Verify that there is good terminal contact in the ECT sensor and Powertrain Control Module (PCM) connectors. Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes, repair as necessary.

No, replace and program the Powertrain Control Module (PCM). Perform the Powertrain Verification Test.

Share this post