1997 PCED OBDII-Diesel | SECTION 5C: Pinpoint Tests |
AL1 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 AL2. |
AL2 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 and ground.
Is resistance less than 5 ohms?
| Yes | No |
|---|
| GO to AL3. | REPAIR open in ground Circuit 57 (BK). |
AL3 CHECK POWER TO TACHOMETER
- Key on/engine off.
- Measure voltage between power Circuit 640 (R/LG), Pin 13 of the black instrument cluster connector and ground.
Is battery voltage present?
| Yes | No |
|---|
| GO to AL4. | REPAIR open in Circuit 640 (R/LG). |
AL4 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 table listed below?
| 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 AL5. |
AL5 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 and Pin 50 (49 State except Econoline) or Pin 19 (California and all Econoline) on the breakout box.
Is resistance less than 5 ohms?
| Yes | No |
|---|
| GO to AL6. | REPAIR open in Circuit 648 (W/PK). |
AL6 CHECK FOR SHORT TO GROUND IN TACH SIGNAL CIRCUIT
- Key off.
- Measure resistance between Circuit 648 (W/PK) Test Pin 50 (49 State except Econoline) or Pin 19 (California and all Econoline) on the breakout box and ground.
Is resistance greater than 10,000 ohms?
| Yes | No |
|---|
| GO to AL7. | REPAIR short to ground in Circuit 648 (W/PK). |
AL7 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 and ground.
Is voltage present?
| Yes | No |
|---|
| REPAIR short to power on Circuit 648 (W/PK). | REPLACE PCM. |
AL: Introduction