My 1996 Ford Ranger failed inspection because of the P0117 (Engine Coolant Temperature Circuit Low Input) diagnostic code. I had the local service center look into it and they reset the code which they said was showing in "history" and not active. Then I immediately tried to get the car re-inspected. The code is still showing and it failed as a result. What is this code and how can it be fixed? I can find no "how to" on fixing this anywhere. Any help is greatly appreciated.

 

It is possible that it may need a coolant temp. sensor. Look in your manual for testing sensor. Most likely you will need a voltmeter to test the circuit.

 

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You didn't say if the current code was a KOEO, KOER or continous so I list the test for all of them.

DA20 DTC P0112 OR P0117: SIMULATE OPPOSITE SIGNAL TO PCM
Diagnostic Trouble Code (DTC) P0117 (ECT) or DTC P0112 (IAT) indicates the sensor signal is less than Self-Test minimum. The IAT and ECT sensor minimum is 0.2 volt 250°F (121°C).

Possible causes:

Grounded circuit in harness.
Damaged sensor.
Improper harness connection.
Damaged PCM.
Key off.
Disconnect vehicle harness from suspect sensor. Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.
Scan Tool installed.
Key on.
Access ECT or IAT PID.
Is the ECT or IAT PID greater than 4.2 volts (less than -40° F/C)?
Yes No
REPLACE sensor. RECONNECT harness. RERUN Quick Test . GO to DA21 .

DA21 CHECK VREF CIRCUIT VOLTAGE AT TP SENSOR
Refer to schematic at the beginning of the pinpoint test.
Key off.
Disconnect TP sensor.
Key on, engine off.
Measure the voltage between VREF circuit and SIG RTN circuit at the TP sensor vehicle harness connector.
Is voltage between 4.0 and 6.0 volts?
Yes No
There is sufficient VREF voltage. RECONNECT TP sensor. GO to DA22 . GO to Pinpoint Test Step C1 .

DA22 CHECK SIGNAL CIRCUIT FOR SHORT TO GROUND
Key off.
Suspect temperature sensor disconnected.
Disconnect PCM. Inspect for damaged or pushed out pins, corrosion, loose wires, etc. Service as necessary.
Install breakout box, PCM disconnected.
Measure resistance between Test Pin 38 (ECT) or 39 (IAT) and Test Pins 24 or 51 (PWR GND) and 91 (SIG RTN) at the breakout box.
Is each resistance greater than 10,000 ohms?
Yes No
REPLACE PCM. REMOVE breakout box. RECONNECT all components. RERUN Quick Test. SERVICE short circuit. REMOVE breakout box. RECONNECT all components. RERUN Quick Test .

DA90 DTCS P0112, P1112, P0113, P0117, P1117 OR P0118: INTERMITTENT CHECK
Diagnostic Trouble Codes (DTCs) P0112, P1112 or P0113 (IAT DTCs) and P0117, P1117 or P0118 (ECT DTCs) are not received during KOEO and KOER Self-Tests, but are output during Continuous Memory Self-Test and may be intermittent.

Possible causes:

Damaged harness.
Damaged harness connector.
Damaged IAT or ECT sensor.
Low coolant (ECT).
Damaged PCM.
Key off.
Scan Tool connected.
Key on.
Monitor the ECT or IAT PID.
While observing the PID, perform the following:
Tap on the sensor to simulate road shock.
Wiggle the sensor connector.
Is there any large change in the temperature reading?
Yes No
DISCONNECT and INSPECT connectors. If OK, REPLACE the sensor. COMPLETE PCM Reset to clear DTCs (REFER to Section 2A, Powertrain Control Module (PCM) Reset ). RERUN Quick Test . For Continuous DTCs P1112 and P1117, COMPLETE Comprehensive Component Monitor Drive Cycle (REFER to Section 2A, Drive Cycles ). GO to DA91 .

DA91 CHECK EEC-V WIRING HARNESS
Still monitoring PID.
While observing the appropriate PID, perform the following:
Hold the vehicle harness close to the sensor connector. Wiggle, shake and bend small sections of wiring harness while working toward the PCM.
Is there any change in the temperature reading?
Yes No
ISOLATE fault. SERVICE as necessary. COMPLETE PCM Reset to clear DTCs (REFER to Section 2A, Powertrain Control Module (PCM) Reset ). RERUN Quick Test. For Continuous DTCs P1112 and P1117, COMPLETE Comprehensive Component Monitor Drive Cycle (REFER to Section 2A, Drive Cycles ). GO to DA92 .

DA92 CHECK PCM AND VEHICLE HARNESS CONNECTOR
Key off.
Disconnect PCM.
Disconnect sensor connector. Inspect for spread terminals, pushed out pins and loose or crimped wires.
Are connectors and terminals OK?
Yes No
Fault is not present at this time. COMPLETE PCM Reset to clear DTCs (REFER to Section 2A, Powertrain Control Module (PCM) Reset ). RERUN Quick Test. For Continuous Memory DTCs P1112 and P1117, COMPLETE Comprehensive Component Monitor Drive Cycle (REFER to Section 2A, Drive Cycles ). SERVICE as necessary. COMPLETE PCM Reset to clear DTCs (REFER to Section 2A, Powertrain Control Module (PCM) Reset ). RERUN Quick Test . For Continuous Memory DTCs P1112 or P1117, COMPLETE Comprehensive Component Monitor Drive Cycle (REFER to Section 2A, Drive Cycles ).

 

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Replace the ECT. It's the two-wire sensor located right next to the T-stat housing. Inspect the harness connecor and wiring while you're in there. Disconnect the battery before you start.

Then drive around for several days, highway and city, so that the computer can complete all the OBDII monitors. You should be good to go after that.