Diagnostic Aids
This test is used to diagnose the following:
- Harness circuit: CTO (Clean Tachometer Output).
- Faulty PCM.
- Faulty TCM.
NOTE:
See TEST DIRECTORY table for starting diagnostic step.
CIRCUIT PIN IDENTIFICATION (PCM)
| Circuit | PCM Pin No. | Wire Color |
|---|---|---|
| CTO | 3 | Green/White |
CIRCUIT PIN IDENTIFICATION (TCM)
| Circuit | TCM Pin No. | Wire Color |
|---|---|---|
| CTO | 15B | Green/White |
TEST DIRECTORY
| Fault | Action |
|---|---|
| Symptom Test; Tachometer Malfunction | Go To Step 1) |
| DTC P0725 | Go To Step 10) |
- 1) Check RPM PID
Turn ignition off. Connect NGS scan tool to OBD-II DLC. Start and run engine. Access RPM PID. Monitor RPM PID while varying engine speed. If RPM PID increases as accelerator pedal is depressed, go to next step. If RPM PID does not increase, fault may be ignition related. Go to TEST DR . - 2) Check RPM Wire To Instrument Cluster For Open Or Short
Turn ignition off. Disconnect PCM and TCM connectors. Inspect harness connector for damage. Disconnect instrument cluster connector. Measure resistance of Clean Tachometer Output (CTO) circuit (Green/White wire) between PCM connector terminal No. 3 and instrument cluster connector. Also measure resistance of CTO circuit (Green/White wire) between PCM connector terminal No. 3 and ground. See Fig 1 and Fig 2 . Also see CIRCUIT PIN IDENTIFICATION (PCM) table. If resistance is less than 5 ohms between PCM connector and instrument cluster, and greater than 10 k/ohms between PCM connector and ground, replace PCM. Restore all electrical connections and repeat QUICK TEST . If either resistance measurement is not as specified, repair open or short in Green/White wire. Restore all electrical connections and repeat QUICK TEST.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. - 10) DTC P0725: RPM Signal To TCM Fault
Turn ignition off. Connect NGS scan tool to fuse panel DLC. Start engine. Select DIAGNOSTIC DATA LINK. Select TCM-TRANSMISSION CONTROL MODULE. Select PID/DATA MONITOR AND RECORD. Access ENG RPM. Read ENG RPM signal while pressing accelerator pedal slowly. If ENG RPM changes according to accelerator pedal position, replace transmission control module. If ENG RPM does not change according to accelerator pedal position, go to next step. - 11) Check CTO Circuit
Turn ignition off. Disconnect TCM and PCM. Measure resistance of CTO circuit (Green/White wire) between TCM connector terminal No. 15B and PCM connector terminal No. 3. Also measure resistance of CTO circuit (Green/White wire) between TCM connector terminal No. 15B and ground. See CIRCUIT PIN IDENTIFICATION (TCM) table. If resistance is less than 5 ohms between TCM connector and PCM connector, and greater than 10 k/ohms between TCM connector and ground, replace TCM. Restore all electrical connections and repeat QUICK TEST . If either resistance is not as specified, repair open or short in Green/White wire. Restore all electrical connections and repeat QUICK TEST.