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 & TCS)
- Faulty Powertrain Control Module (PCM)
- 1) KOER DTC P1780: Check Transmission Control Switch Function
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
- TCS Circuit Open Or Shorted
- Faulty PCM
Turn ignition switch to ON position. Using scan tool, select TCS PID from PID/DATA MONITOR & RECORD menu. Cycle TCS switch. Then hold switch depressed for 3 seconds, then release switch. 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 value is not as specified, go to next step.
- 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 of TCS circuit between negative battery terminal and PCM harness connector terminal No. 29 while cycling TCS. See Figure and Fig 1 . If voltage measurement does not cycle when TCS is cycled, go to next step. If voltage measurement 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 terminal No. 29. 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 terminal No. 29. Also, measure resistance of TCS KEY PWR circuit between TCS harness connector and appropriate TCS fuse in junction box. See Figure and Fig 1 . See WIRING DIAGRAMS article. If both resistance measurements are less than 5 ohms, go to next step. If any resistance measurement is 5 ohms or more, repair open TCS circuit. - 5) Check TCS Circuit For Short To VPWR In Harness
Measure resistance between PCM harness connector terminals No. 29 (TCS) and No. 71 (VPWR). If resistance is more than 10 k/ohms, replace 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 light changes state, fault is unable to be duplicated at this time. Go to TEST Z, step 1). If TCIL light does not change state, 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 on, repair short to ground in TCIL circuit. See Fig 1. See WIRING DIAGRAMS article. - 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 PCM harness connector TCIL circuit terminal. See Fig 1. If voltage is more than 2 volts, check wiring harness between TCIL and PCM for an open or short circuit. 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 article. - 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 ground and TCS harness connector terminal No. 1 (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 betwen TCS and central junction box. - 11) Check Transmission Control Switch Resistance
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 pressed, and more than 10 k/ohms with TCS released. If resistance is within specification, go to next step. If resistance is not within specification, replace TCS. Verify system operation. - 12) Check O/D CANCEL SW Circuit (Light Blue/Yellow Wire) For Open
Ensure ignition switch is turned to OFF position. Disconnect Instrument Cluster Module (ICM) 22-pin connector C241. Using a DVOM, measure resistance of Light Blue/Yellow wire between TCS harness connector and ICM harness connector C241 terminal No. 21. See Fig 2. 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:
Steps 6)- 9)
are performed when directed here from WARNING INDICATOR LIGHTS under SYMPTOMS in TROUBLE SHOOTING - NO CODES article.