1996 PCED OBDI | SECTION 18: Diesel Diagnosis — 7.3L DI Engine |
AQ1 TACHOMETER INOPERATIVE: CHECK FUSE 17
- Check fuse 17 in IP fuse panel for open.
Is fuse blown?
| Yes | No |
|---|
| REPAIR short to ground in Circuit 640 (R/Y). REPLACE fuse. | GO to AQ2. |
AQ2 CHECK GROUND TO TACHOMETER
- Key off.
- Disconnect instrument cluster and inspect for damaged pins.
- Measure resistance between ground Circuit 57 (BK), Pin 3 of the black instrument cluster connector to ground.
Is resistance less than 5 ohms?
| Yes | No |
|---|
| GO to AQ3. | REPAIR open in ground Circuit 57 (BK). |
AQ3 CHECK POWER TO TACHOMETER
- Key on/engine off.
- Measure voltage between power Circuit 640 (R/LG), Pin 13 of the black instrument cluster connector to ground.
Is battery voltage present?
| Yes | No |
|---|
| GO to AQ4. | REPAIR open in Circuit 640 (R/LG). |
AQ4 CHECK SIGNAL CIRCUIT OUTPUT
- Use the NGS Tester plugged into the data link connector (DLC) and two jumpers, one plugged between the COM port of the NGS Tester to Pin 3 (ground) of the black instrument cluster connector and the other jumper plugged between the SIG port of the NGS Tester to Pin 9 (tach signal) of the black instrument cluster connector.
- Key on, engine running.
- With NGS Tester, select VEHICLE and ENGINE.
- Select DIGITAL MEASUREMENT SYSTEM.
- Select FREQUENCY METER.
- Change level to 4 VOLT DC.
- Press the LINK button to choose a pid.
- Select PID/DATA MONITOR.
- Select the RPM PID.
- Press start.
- Take three readings at 650 rpm, 1500 rpm and 3000 rpm.
Do readings match the listed table?
| Step No.
| Step 1 | Step 2 | Step 3 |
|---|
| RPM | 650 rpm | 1500 rpm | 3000 rpm |
| Frequency | 129 ± 10 Hz | 300 ± 10 Hz | 600 ± 10 Hz |
| Yes | No |
|---|
| INSPECT printed circuit board for damaged or open circuits. If OK, REPLACE tachometer. | GO to AQ5. |
AQ5 CHECK FOR OPEN IN TACH SIGNAL CIRCUIT
- Key off.
- Disconnect PCM and inspect for damaged pins. Service as necessary.
- Install breakout box, leave PCM disconnected.
- Measure resistance on Circuit 648 (W/PK) between Pin 9 of the black instrument cluster connector to Pin 50 on the breakout box.
Is resistance less than 5 ohms?
| Yes | No |
|---|
| GO to AQ6. | REPAIR open in Circuit 648 (W/PK). |
AQ6 CHECK FOR SHORT TO GROUND IN TACH SIGNAL CIRCUIT
- Key off.
- Measure resistance between Circuit 648 (W/PK) Test Pin 50 on the breakout box to ground.
Is resistance greater than 10,000 ohms?
| Yes | No |
|---|
| GO to AQ7. | REPAIR short to ground in Circuit 648 (W/PK). |
AQ7 CHECK FOR SHORT TO POWER IN TACH SIGNAL CIRCUIT
- Key on/engine off.
- Measure voltage between Circuit 648 (W/PK) Test Pin 50 on the breakout box to ground.
Is voltage present?
| Yes | No |
|---|
| REPAIR short to power on Circuit 648 (W/PK). | REPLACE PCM. |
AQ: Introduction