Diagnostic Aids

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the following:

• Wiring harness circuits (TCIL and TCS)..
• Faulty Powertrain Control Module (PCM).

1. 1) DTC P1780
   
   This DTC indicates Transmission Control Switch (TCS) was not cycled during KOER self-test. Possible causes are:
   • Faulty TCS.
   • TCS not cycled during self-test.
   • Open or short in wiring harness.
   • Faulty PCM.

   Turn ignition on. Using scan tool, select TCS PID. Cycle TCS switch, then hold switch depressed. If PID value switched from ON to OFF, then indicated ON when switch was depressed, repeat KOER ON-DEMAND SELF-TEST  to cycle TCS. If PID value is not as specified, go to next step.

2. 2) Check TCS Circuit Voltage
   
   Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition on. Measure voltage between PCM connector pin No. 29 (TCS) and negative battery terminal while cycling TCS. If voltage reading does not cycle when TCS is cycled, go to next step. If voltage reading cycles when TCS is cycled, replace PCM and repeat QUICK TEST .
3. 3) Check Circuit For Short To Ground
   
   Turn ignition off. Disconnect TCS connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between PCM connector pin No. 29 (TCS) and negative battery terminal. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short to ground in TCS circuit.
4. 4) Check Continuity Of TCS Circuits
   
   Connect ohmmeter positive lead to TCS key power at the fuse panel. Connect negative lead to power terminal at TCS wiring harness connector. Note resistance reading. Measure resistance between PCM connector pin No. 29 (TCS) and TCS terminal at TCS wiring harness connector. If both resistance readings are less than 5 ohms, go to next step. If any resistance reading is 5 ohms or more, repair open TCS circuit.
5. 5) Check Circuit For Short To Power
   
   Measure resistance between PCM connector pins No. 29 (TCS) and No. 71 (VPWR). If resistance is more than 10,000 ohms, replace TCS. If resistance is 10,000 ohms or less, repair short to power in TCS circuit.
6. 6) Check TCIL PID
   
   Turn ignition on. Using scan tool, select TCIL PID. Cycle TCS. If PID value changes from ON to OFF, fault is intermittent. Go to TEST Z . If PID value does not change from ON to OFF, go to next step.
7. 7) Check For Short to Ground In TCIL Circuit
   
   Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition on. If TCIL turns off, replace PCM. If TCIL remains on, repair short to ground in TCIL circuit.
8. 8) Check For DTC P1780
   
   Perform KOER ON-DEMAND SELF-TEST . If DTC P1780 is not present, go to next step. If DTC P1780 is present, go to step  1.
9. 9) Check Voltage To TCIL
   
   Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition on. Measure voltage between TCIL PCM connector pin and negative battery terminal. See Fig 1-Fig 3 . If both voltage is more than 2 volts, replace PCM. If voltage is 2 volts or less, check indicator bulb and fuse. Repair as necessary. If bulb and fuse are okay, repair open in circuit between PCM connector pin No. 79 and ignition switch.
   Fig 1: TCIL & TCS Circuit Schematic (Contour, Cougar & Mystique)

   Courtesy of FORD MOTOR CO.
   Fig 2: TCIL & TCS Circuit Schematic (Econoline, Expedition, Navigator, Pickup & Windstar)

   Courtesy of FORD MOTOR CO.
   Fig 3: TCIL & TCS Circuit Schematic (All Other Models)

   Courtesy of FORD MOTOR CO.