Diagnostic Aids

Perform this test only when directed here.

This test is intended to diagnose the following components and circuits:

• Engine Coolant Temperature (ECT) sensor.
• Intake Air Temperature (IAT) sensor.
• Harness circuits; IAT and ECT.
• PCM.

To prevent replacing good components, ensure the following are not the cause of problem:

• Coolant level low.
• Cooling system, water pump or fan.
• Engine operating temperature.
• Engine oil level low.
• Thermostat.
• Air cleaner duct.
• Ambient temperature.

NOTE: For diagnosis of DTC P0125, go to step  100). For diagnosis of DTC P1217, go to step  19).
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 1)  to step 10)  . No test procedures have been omitted.
1. 1) DTC P0110 Or P0115
   DTC P0110 indicates malfunction in IAT sensor circuit. DTC P0115 indicates malfunction in ECT sensor circuit. Possible causes are as follows:
   • Open in harness.
   • Faulty harness connection.
   • Faulty sensor.
   • Faulty PCM.

   Turn ignition off. Connect NGS tester to DLC. Turn ignition on. Access ECT or IAT PID. If ECT or IAT PID reads between -4°F (-20°C) and 300°F (149°C), sensors are within acceptable range and fault may be intermittent. See TEST Z  for intermittent diagnostics. If ECT and IAT PIDs read greater than 300°F (149°C), go to step  20). If IAT and ECT PIDs read less than -4°F (-20°C), go to step  10).

2. 10) Simulate High Temperature Signal
   
   Turn ignition off. Disconnect suspect temperature sensor. Connect a jumper wire between the suspect sensor signal terminal and SIG RTN terminal at sensor harness connector. See CIRCUIT PIN IDENTIFICATION  table. Turn ignition on. Using New Generation Star (NGS) tester, access ECT or IAT PID.
   NOTE: If tester has a communication problem, disconnect jumper wire immediately and go to step  12).

   If ECT or IAT PIDs read greater than 300°F (149°C), replace suspect sensor, restore wiring connections and rerun QUICK TEST . If ECT or IAT PIDs do not read greater than 300°F (149°C), remove jumper wire and go to next step.

   Fig 1: Identifying Engine Coolant & Intake Air Temperature Sensor Circuits & Harness Connector Terminals

   Courtesy of FORD MOTOR CO.
3. 11) Check Sensor Wiring
   
   Turn ignition off. Disconnect PCM harness connector. Inspect connectors for damage, pushed out pins, corrosion, etc. Measure resistance between signal pin at sensor connector and PCM connector terminals No. 59 (ECT) or No. 61 (IAT). Measure resistance between SIG RTN pin at sensor connector (Black/Yellow wire) and PCM connector terminal No. 58 (SIG RTN). See Fig 1. If each resistance reading is less than 5 ohms, go to next step. If any resistance reading is not less than 5 ohms, repair open in circuit.
4. 12) Check Sensor Signal For Short-To-VREF
   
   Turn ignition off. Measure resistance between PCM connector terminals No. 59 (ECT) or No. 61 (IAT) and VREF terminal No. 57 (Brown wire). If all resistance readings are greater than 10 k/ohms, replace PCM and repeat QUICK TEST . If any resistance reading is less than 10 k/ohms, locate and repair wire shorted to VREF.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 12)  to step 19)  . No test procedures have been omitted.
5. 19) Engine Overheat Condition (DTC P1217)
   
   If an engine overheat condition was sensed by ECT sensor, check coolant level or check for internal or external coolant leaks. Check for blockage of radiator and proper cooling fan operation. Repair as necessary. If cooling system is okay, go to next step.
6. 20) Simulate High Level Signal To PCM
   
   Turn ignition off. Disconnect suspect sensor. Connect NGS tester to DLC. Turn ignition on. Access ECT or IAT PID. If ECT or IAT sensor PID reads less than -4°F (-20°C), replace sensor. Reconnect all electrical connections and repeat QUICK TEST . If ECT or IAT sensor PID reads greater than -4°F (-20°C), go to next step.
7. 21) Check VREF At TP Sensor
   
   Turn ignition off. Disconnect Throttle Position (TP) sensor harness connector. Turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor connector. See Figure. If voltage is 4.5-5.5 volts, go to next step. If voltage is not 4.5-5.5 volts, go to TEST C .
8. 22) Signal Circuit Short To Ground
   
   Turn ignition off. Disconnect PCM. Measure resistance between ECT or IAT ground and SIG RTN circuits at PCM harness connector. If each resistance reading is greater than 10 k/ohms, replace PCM. If any of the resistance reading is less than 10 k/ohms, repair short in circuit.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 22)  to step 100)  . No test procedures have been omitted.
9. 100) DTC P0125: Excessive Time To Enter Closed Loop
   
   This DTC indicates ECT sensor has not reached required temperature to initiate closed loop within a specified amount of time. Possible causes are low coolant level, or leaky or stuck thermostat. Ensure sufficient warm-up period is allowed. Check coolant level and replenish as necessary. If coolant level is okay, replace thermostat. Clear all DTCs and repeat QUICK TEST .