Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 14 other vehicles, including the 1996 Ford RV Cutaway, 1996 Ford Pickup, 1996 Ford F-Super Duty, 1996 Ford Econoline, and 1996 Ford Cutaway. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test only when directed here by QUICK TEST or if no DTCs are present and tachometer is inoperative. This pinpoint test is intended to diagnose:

Wiring harness circuits; (KEY PWR, GND and TACH signal).
Tachometer.

Fig 1: Identifying Tachometer Circuit

1) Check Fuse

Remove and inspect fuse No. 17 in instrument panel fuse block. If fuse is blown, locate and repair short to ground in Red/Yellow wire (circuit No. 640). Replace fuse. If fuse is okay, go to next step.

2) Check Ground Circuit

Turn ignition off. Disconnect instrument cluster Black 14-pin connector and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Measure resistance between ground and terminal No. 3 at instrument cluster wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, locate and repair open in ground circuit (Black wire).

3) Check Power To Tachometer

Turn ignition on. Measure voltage between ground and terminal No. 13 (Red/Light Green wire) at instrument cluster wiring harness connector. If battery voltage is present, go to next step. If battery voltage is not present, locate and repair open in Red/Light Green wire.

4) Check Signal Circuit

Connect New Generation Star (NGS) tester to Data Link Connector (DLC). Connect a jumper wire between terminal No. 3 (Black wire) at instrument cluster wiring harness connector and COM port at NGS tester. Connect another jumper wire between terminal No. 9 (White/Pink wire) at instrument cluster wiring harness connector and SIG port at NGS tester. Start engine. Using NGS tester, perform the following:

Select VEHICLE and ENGINE.
Select DIGITAL MEASUREMENT SYSTEM.
Select FREQUENCY METER.
Change level to 4-volt DC.
Press LINK button to select a PID.
Select PID/DATA MONITOR.
Select RPM PID.
Press START.

Observe PID reading at specified engine RPM. See RPM PID FREQUENCY SPECIFICATIONS table. If frequency is as specified, inspect instrument cluster printed circuit board for damage or open circuits. Repair as necessary. If printed circuit board is okay, replace tachometer. If frequency is not as specified, go to next step.

RPM PID FREQUENCY SPECIFICATIONS

RPM	Hz
650	119-139
1500	290-310
3000	590-610

5) Check For Open In TACH Signal Circuit

Turn ignition off. Disconnect PCM 104-pin connector, and inspect for damaged pins, corrosion and loose wires. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between terminal No. 9 (White/Pink wire) at instrument cluster wiring harness connector and test pin No. 50 at breakout box. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, locate and repair open circuit in White/Pink wire.

6) Check For Short To Ground

Measure resistance between ground and test pin No. 50 at breakout box. If resistance is more than 10 k/ohms, go to next step. If resistance is 10 k/ohms or less, locate and repair short to ground in White/Pink wire.

7) Check For Short To Power

Turn ignition on. Measure voltage between ground and test pin No. 50 at breakout box. If battery voltage is present, locate and repair short to power in White/Pink wire. If battery voltage is not present, replace PCM.