Diagnostic Aids

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

• TP sensor.
• Wiring harness circuits (TP, SIG RTN and VREF).
• Powertrain Control Module (PCM).

Normal range of throttle angle measurement for TP sensor is 0-85 degrees. To pass QUICK TEST  procedure, range of throttle rotation (in degrees) must be within 3 percent of specification. See Fig 2 .

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.
• Choke cam adjustment (if equipped).
• TP sensor not seated.

Fig 1: TP Sensor Circuit & Connector Terminal ID (Bronco)

Fig 2: TP Sensor Specification Chart (Bronco)

1) KOER Code 121: Check For Other Codes  KOER Code 121 indicates TP sensor rotational setting may be out of self-test range. Possible causes for this fault are:

• Binding throttle linkage.
• TP sensor not seated correctly.
• Faulty TP sensor.
• Faulty Powertrain Control Module (PCM).

Perform KOER SELF-TEST. Check for Code 327. If Code 327 is present with Code 121, service Code 327 and repeat QUICK TEST  . If Code 327 is not present, go to next step.

2) KOEO Code 121: Check For Binding Throttle Plate  Inspect throttle body for binding. If throttle body is binding, check for binding throttle or cruise control linkage, vacuum line or harness interference, etc. Repair as necessary, and repeat QUICK TEST. If no mechanical problem is found, go to next step.

3) Code 123: Attempt To Generate Code 122  Code 123 indicates TP sensor signal is greater than self-test maximum value. Possible causes for this fault are:

• TP sensor not seated properly.
• Faulty TP sensor.
• Short circuit to power.
• Faulty PCM.

Turn ignition off. Disconnect TP sensor wiring harness connector. Inspect and repair connector pins if damaged. Repeat KOEO SELF-TEST. Ignore all other codes at this time. If Code 122 is not displayed, go to step 5). If Code 122 is displayed, go to next step.

4) Check VREF Circuit Voltage  Turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. If reading is 4-6 volts, replace TP sensor and repeat QUICK TEST  . If reading is not 4-6 volts, reconnect sensor and go to CIRCUIT TEST C.

5) Check TP Circuit For Short To Power  Turn ignition off. Leave TP sensor disconnected. Disconnect PCM 60-pin connector. Inspect it for damage and repair as necessary. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 47 and test pins No. 26 and 57. If either resistance is less than 10,000 ohms, repair short circuit in wiring harness and repeat QUICK TEST  . If both resistances are 10,000 ohms or more, replace PCM and repeat QUICK TEST.

10) Code 122: Attempt To Generate Code 121 Or 123  Code 122 indicates TP signal is less than minimum self-test value. See Fig 2 . Possible causes for this fault are:

• TP sensor not seated correctly.
• Faulty TP sensor.
• Open circuit in wiring harness.
• Grounded circuit in wiring harness.
• Faulty PCM.

Turn ignition off, and wait 10 seconds. Disconnect TP sensor from harness. Install a jumper wire between VREF and TP terminals at TP sensor wiring harness connector. Perform KOEO SELF-TEST. If no codes are generated, remove jumper wire and go to step 13). If Codes 121 and 123 are not present, remove jumper wire and go to next step. If either Code 121 or 123 is displayed, replace TP sensor and repeat QUICK TEST  .

11) Check VREF Circuit Voltage  Turn ignition on. Measure voltage between VREF and SIG RTN terminals at TP sensor wiring harness connector. If voltage is not 4-6 volts, reconnect all components and go to CIRCUIT TEST C. If voltage is 4-6 volts, go to next step.

12) Check TP Sensor Circuit Continuity  Turn ignition off. Leave TP sensor disconnected. Disconnect PCM 60-pin connector. Inspect connector and repair if necessary. Install Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between TP terminal at TP sensor wiring harness connector and test pin No. 47. If resistance is 5 ohms or more, repair open circuit and repeat QUICK TEST  . If resistance is less than 5 ohms, go to next step.

13) Check TP Circuit For Shorts To Ground  Turn ignition off. Leave TP sensor disconnected. Disconnect PCM 60-pin connector. Inspect wiring, and repair as necessary. With breakout box installed, measure resistance between test pin No. 47 and test pins No. 40, 46 and 60. If any reading is less than 10,000 ohms, repair short circuit and repeat QUICK TEST. If all readings are 10,000 ohms or more, replace PCM and repeat QUICK TEST.

20) Code 167: Repeat Dynamic Response Test  KOER Code 167 indicates TP sensor did not exceed 25 percent rotation during dynamic response portion of KOER SELF-TEST. A complete Wide Open Throttle (WOT) must be performed during dynamic response portion of test. Perform KOER SELF-TEST. Ensure WOT is completed during dynamic response portion of test. If Code 167 is still present, go to next step. If code is not present, system is unable to duplicate Code 167 at this time. Service any other KOER codes. If no other service codes are present, testing is complete.

21)  Check TP Sensor Movement During Dynamic Response Test -Turn ignition off. Disconnect PCM 60-pin connector. Inspect wiring, and repair as necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM connected. Set DVOM on 20-volt scale. Connect DVOM between test pins No. 46 and 47 at breakout box. Perform KOER SELF-TEST and ensure proper WOT is completed during dynamic response test. If DVOM reading exceeds 3.5 volts during dynamic response test, replace PCM and repeat QUICK TEST  . If reading does not exceed 3.5 volts, ensure TP sensor is correctly installed and adjusted. If TP sensor is correctly installed and adjusted, replace TP sensor. Repeat QUICK TEST.

90) Continuous Memory Code 123  This test monitors TP sensor under simulated road conditions. Enter wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST)  under QUICK TEST. Connect DVOM or diagnostic tester to STO terminal of Data Link Connector (DLC). While slowly opening throttle to WOT, observe DVOM or diagnostic tester for indication of fault. Slowly bring throttle to closed position. Lightly tap TP sensor and wiggle harness connector. This test checks for open or short in TP sensor and wiring harness. If no fault is indicated, go to step 92). If fault is indicated, go to next step.

91) Measure TP Circuit Voltage While Exercising TP Sensor  Turn ignition off, and wait 10 seconds. Disconnect PCM 60-pin connector. Inspect for damage and repair if necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM connected. Stay in wiggle test (as in previous step). Connect DVOM between test pins No. 47 and 46. Set DVOM on 20-volt scale. With ignition on and engine off, observe DVOM and repeat step 90). If fault occurs at less than 4.25 volts, inspect TP sensor connectors and terminals. If connectors and terminals are okay, replace TP sensor, clear codes and repeat QUICK TEST. If fault does not occur at less than 4.25 volts, TP sensor over-travel may have caused Continuous Memory Code 123. TP sensor is okay; go to next step to check wiring harness.

92) Check EEC-IV Wiring Harness  While in wiggle test, bend and shake small sections of wiring harness from TP sensor wiring harness connector to firewall and from firewall to PCM while observing analog voltmeter or scan tester. If fault is indicated, isolate fault in wiring and repair as necessary. Clear codes, and repeat QUICK TEST  . If no fault is indicated, go to next step.

93) Check PCM & Harness Connectors  Turn ignition off, and wait 10 seconds. Disconnect PCM 60-pin connector from breakout box. Inspect connectors and terminals for damage, and repair as necessary. Clear codes from PCM memory, and repeat QUICK TEST  . If connectors and terminals are okay, fault cannot be duplicated at this time. Continuous Memory Code 123 testing is complete.

94) Continuous Memory Code 122  Enter wiggle test. See CONTINUOUS MONITOR MODE (WIGGLE TEST)  under QUICK TEST. Connect DVOM or diagnostic tester to STO terminal of Data Link Connector (DLC). Observe DVOM or diagnostic tester for indication of fault while performing the following:

• Slowly open throttle to WOT.
• Slowly bring throttle to closed position.
• Lightly tap TP sensor and wiggle connector.

If fault is indicated, disconnect TP sensor. Inspect connectors and terminals. If connectors and terminals are okay, replace TP sensor. Clear codes from PCM memory, and repeat QUICK TEST  . If no fault is indicated, go to next step.

95) Check EEC-IV Wiring Harness  Stay in wiggle test (as in previous step). Bend, wiggle and shake small sections of wiring harness from TP sensor wiring harness connector to firewall and from firewall to PCM while observing analog voltmeter or scan tester. If fault is indicated, isolate fault in wiring and repair as necessary. Clear codes from PCM memory, and repeat QUICK TEST. If no fault is indicated, go to next step.

96) Check PCM & Harness Connectors  Turn ignition off. Inspect PCM 60-pin connector and terminals for damage. Repair connector terminals if necessary. Clear codes from PCM memory, and repeat QUICK TEST  . If connectors and terminals are okay, fault cannot be duplicated at this time. Continuous Memory Code 122 testing is complete.