Test Tb: Transmission Control Switch/Transmission Control Indicator Lamp: Testing
- 1) For KOER Only DTC P1780: Check Transmission Control Switch Function
DTC P1780 indicates Transmission Control Switch (TCS) was not cycled during KOER self-test. Possible causes are:- TCS Not Cycled During Self-Test
- Faulty TCS
- TCS Circuit Open Or Shorted
- Faulty PCM
Turn ignition switch to ON position. Using scan tool, access TCS PID from PID/DATA MONITOR & RECORD menu. Cycle TCS switch, hold switch depressed for 3 seconds, then release switch. Turn ignition switch to OFF position. If TCS PID value switched from ON to OFF, then indicated ON when switch was depressed, repeat KOER ON-DEMAND SELF-TEST , ensuring to cycle TCS. If TCS PID did not indicate as specified, go to step 10) (Windstar), or next step (all others).
- 2) Check Voltage To TCS
Turn ignition switch to OFF position. Disconnect PCM connector(s). Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition switch to ON position. Using a DVOM, measure voltage between negative battery terminal and TCS circuit at PCM harness connector while cycling TCS. See PCM CONNECTOR IDENTIFICATION and Figure-Figure . If voltage does not cycle when TCS is cycled, go to next step. If voltage cycles when TCS is cycled, replace PCM and repeat QUICK TEST . - 3) Check TCS Circuit For Short To Ground In Harness
Turn ignition switch to OFF position. Disconnect TCS connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Using a DVOM, measure resistance of TCS circuit between negative battery terminal and PCM harness connector. If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, repair short to ground in TCS circuit. - 4) Check TCS Circuit For Open In Harness
Using a DVOM, measure resistance of TCS circuit between TCS harness connector and PCM harness connector. Also, measure resistance of TCS KEY PWR circuit between TCS harness connector and appropriate TCS fuse in junction box. See PCM CONNECTOR IDENTIFICATION and Figure-Figure . See WIRING DIAGRAMS for TCS fuse identification. If both resistances are less than 5 ohms, go to next step. If either resistance is 5 ohms or more, repair open TCS circuit. - 5) Check TCS Circuit For Short To PWR In Harness
Using a DVOM, measure resistance between TCS and VPWR circuits at PCM harness connector. If resistance is more than 10 k/ohms, replace faulty TCS. If resistance is 10 k/ohms or less, repair short to VPWR in TCS circuit. - 6) TCIL Always ON With Engine Running (No DTCs): Check TCIL Function
Turn ignition switch to ON position. Cycle Transmission Control Switch (TCS). If TCIL illuminates and then goes off, fault is unable to be duplicated at this time. Go to TEST Z, step 1). If TCIL does not illuminate and then go off, go to next step. - 7) Check TCIL Circuit For Short to Ground In Harness
Turn ignition switch to OFF position. Disconnect PCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition switch to ON position. If TCIL turned off with PCM disconnected, replace PCM. If TCIL remains illuminated, repair short to ground in TCIL circuit. See Figure-Figure . See WIRING DIAGRAMS . - 8) TCIL Never ON: 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) Check Voltage To TCIL
Turn ignition switch to OFF position. Disconnect PCM connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Turn ignition switch to ON position. Using a DVOM, measure voltage between negative battery terminal and TCIL circuit at PCM harness connector. See PCM CONNECTOR IDENTIFICATION and Figure-Figure . If voltage is more than 2 volts, check wiring harness between TCIL and PCM for an open or short circuit. See WIRING DIAGRAMS . If no fault exists, replace PCM. If voltage is 2 volts or less, check TCIL bulb and fuse. Repair as necessary. If bulb and fuse are okay, repair open in circuit between PCM harness connector and TCIL, or between TCIL and power supply. See WIRING DIAGRAMS . - 10) Check VPWR Voltage To Transmission Control Switch
Turn ignition switch to OFF position. Disconnect Transmission Control Switch (TCS) connector. Turn ignition switch to ON position. Using a DVOM, measure voltage between chassis ground and VPWR circuit at TCS harness connector terminal No. 2 (Red/Yellow wire). If voltage is more than 10 volts, go to next step. If voltage is 10 volts or less, repair open in Red/Yellow wire between TCS and central junction box. See ANALOG INSTRUMENT PANELS in appropriate SYSTEM WIRING DIAGRAMS article in ELECTRICAL. Verify system operation. - 11) Check Transmission Control Switch
Turn ignition switch to OFF position. Using a DVOM, measure resistance between both TCS terminals, while pressing and releasing switch. Resistance should be less than 5 ohms with TCS button depressed, and more than 10 k/ohms with TCS button released. If resistance is as specified, go to next step. If resistance is not as specified, replace TCS. Verify system operation. - 12) Check Light Blue/Yellow Wire For An Open
Ensure ignition switch is turned to OFF position. Disconnect Instrument Cluster Module (ICM) 22-pin connector C220c. Using a DVOM, measure resistance of Light Blue/Yellow wire between TCS harness connector and ICM harness connector C220c terminal No. 21. See Fig 1. If resistance is less than 5 ohms, replace ICM. Verify system operation. If resistance is 5 ohms or more, repair open in Light Blue/Yellow wire between TCS and ICM. Verify system operation.
NOTE:
For additional testing information, see DIAGNOSTIC AIDS .
NOTE:
Diagnostic procedures beginning with step 6) are performed when directed here from WARNING INDICATOR LIGHTS under SYMPTOMS in TROUBLE SHOOTING - NO CODES - CNG, FLEX-FUEL & GASOLINE article.