Diagnostic Aids

Perform this test only when directed by QUICK TEST. This test is intended to diagnose the following:

• Throttle Position (TP) sensor.
• SIG RTN, TP SIG and VREF harness circuits.
• PCM.

To prevent replacement of good components, be aware the following non-EEC related areas may be at fault:

• Idle speed.
• Binding throttle shaft or linkage.
• TP sensor not seated.

1. 1) DTC P0120
   
   DTC P0120 indicates TP circuit malfunction. Possible causes for this fault are:
   • Binding throttle shaft or linkage.
   • Faulty TP sensor.
   • TP sensor or throttle stop adjustment.
   • Open or short in harness.
   • Faulty PCM.

   If throttle plate is binding, repair and repeat QUICK TEST . If throttle plate and linkage is okay, go to next step.

2. 2) Check TP PID
   
   Turn ignition off. Connect New Generation Star (NGS) tester to DLC. Turn ignition on. Using NGS tester, access TP PID. If TP PID is .35-4.60 volts, go to step  30). If TP PID is less than .35 volt, go to step  10). If voltage is greater than 4.60 volts, go to step  20).
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 2)  to step 10)  . No test procedures have been omitted.
3. 10) Check VREF Circuit Voltage
   
   Disconnect TP harness sensor. Turn ignition on, with engine off. Measure voltage between VREF and SIG RTN circuits at TP sensor harness connector. See Fig 1. If voltage is about 4.5-5.5 volts, go to next step. If voltage is not about 4.5-5.5 volts, go to TEST C .
   Fig 1: Identifying TP Sensor Circuit & Harness Connector Terminals

   Courtesy of FORD MOTOR CO.
4. 11) Simulate High TP Signal
   
   Connect a jumper wire between TP sensor harness connector TP signal and VREF circuit. Turn ignition on. Using NGS tester, access TP PID. If TP PID is not greater than 4.5 volts, go to next step. If TP PID is greater than 4.5 volts, replace TP sensor.
5. 12) Check TP Circuit Continuity
   
   Turn ignition off. Disconnect PCM harness connector. Measure resistance of TP signal and SIG TRN circuits between TP harness connector and PCM harness connector. See CIRCUIT PIN IDENTIFICATION  table. See Fig 1. If resistance readings are less than 5 ohms, go to next step. If resistance readings are not less than 5 ohms, repair open in circuit.
6. 13) Check TP Circuit For Short To Ground
   
   Leave TP sensor disconnected. Ensure PCM is disconnected. Measure resistance between TP and SIG RTN, and GND circuits at PCM harness connector. If all resistance measurements are greater than 10 k/ohms, replace PCM. If any resistance measurement is not greater than 10 k/ohms, repair short in circuit.
   NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 13)  to step 20)  . No test procedures have been omitted.
7. 20) Simulate Low TP Signal
   
   Turn ignition off. Disconnect TP harness sensor. Connect jumper wire between TP signal and SIG RTN circuits at TP sensor harness connector. See Fig 1. Turn ignition on. Using NGS tester, access TP PID. If TP PID is not less than .2 volt, go to next step. If TP PID is less than .2 volt, replace TP sensor.
8. 21) Check TP & SIG RTN Circuit Continuity
   
   Turn ignition off. Disconnect PCM harness connector. Measure resistance between TP signal circuit and SIG RTN between TP sensor harness connector and PCM harness connector. If both resistance measurements are less than 5 ohms, go to next step. If either resistance is not less than 5 ohms, repair open in circuit(s).
9. 22) Check TP Circuit For Short To VREF
   
   Measure resistance between TP and VREF circuits at PCM harness connector. If resistance is greater than 10 k/ohms, replace PCM. If resistance is not greater 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 30)  . No test procedures have been omitted.
10. 30) Check TP Sensor Signal To PCM
    
    Turn ignition off. Connect New Generation Star (NGS) tester to DLC. Turn ignition on. Using NGS tester, access TP PID. Slowly open throttle from idle to WOT position. Observe TP PID value. See THROTTLE POSITION SENSOR OUTPUT  table. If voltage is not as specified, replace TP sensor. If voltage is as specified, fault may be intermittent. Go to TEST Z  or TROUBLE SHOOTING - NO CODES - VILLAGER article.
    THROTTLE POSITION SENSOR OUTPUT
    
    

    Throttle Position	Volts
    Closed	.4
    1/4	1.3
    Half Open	2.2
    3/4	3.1
    Fully Open	4.1